Electrical Fundamentals for AV

Introduction

Every piece of AV equipment on a show runs on power, and every technician plugs something in on their first day. Most never think about it again until a breaker trips in the middle of a keynote, a cable reel melts under a stage, or somebody gets a tingle from a microphone.

Those three events have the same root. Somebody used power without knowing how much they were asking of it, what protects it, or where their own job ended and an electrician's began. None of it requires becoming an electrician. It requires knowing volts, amps and watts well enough to plan a load, knowing what distribution and cable can carry, respecting the protections that keep people alive, and recognising the moment a task stops being yours.

What this book covers

Volts, amps, watts and resistance; how power is supplied, in single and three phase, and what each conductor does; distribution from the service or generator to the gear; cable, connectors and voltage drop; calculating and planning load across circuits and phases; grounding, GFCI and circuit protection; electrical safety, from shock and arc flash to batteries and weather; clean power for audio and video; and the routes to becoming a licensed electrician or a certified entertainment electrician.

It was measured against the certification outline for entertainment electricians, the standard text on electricity for entertainment technicians, the electrical code articles and safety standards that govern show power, and the codes of practice for temporary event power, so that nothing a technician is taught elsewhere about using power safely is missing here.

What this book does not do

It does not qualify you to do electrical work. Connecting to a building's supply, making tie-ins, working inside distribution or panels, and installing or altering wiring belong to qualified, and in most places licensed, electricians. This book teaches you to use power safely, plan it, and recognise that line every time you reach it.

How to Use This Book

Each chapter follows the same shape, and the shape matters more than it might look. You read the ideas, then you see them play out in a real situation, then you get the procedure, then you are shown what goes wrong and how to recognise it early. Reading only the parts that look new is the fastest way to arrive on a job holding half of something.

1. Read the chapter body first. This is the understanding layer, and it is written to be read straight through.
2. Read On the job. The same material as a real situation on a real show, which is where it stops being abstract.
3. Work through How to do it. These are procedures you can follow on a job this week.
4. Study What goes wrong. Experienced technicians are not people who never make mistakes; they are people who recognise mistakes early.
5. Do the exercise before reading the answer key. Recognition feels like learning and is not.
6. Take the checklist with you. Photograph it on your phone. Use it until you no longer need it.

Keep a notebook

One habit is worth starting today, before the first chapter: keep a small notebook and write the numbers in it as you meet them. Power is arithmetic — watts equals volts times amps, the capacity of a 20 amp circuit at 80 per cent, the draw of the amplifier rack at one-eighth power, the typical and maximum draw of a panel of LED wall, the voltage of the country you are working in, and who the show electrician is today.

Write it by hand rather than photographing this page. Copying a number puts it on paper; working the calculation yourself is what puts it in your head, and deciding how to set it out is most of the understanding.

Then use it twice. Read a few pages on the way to a job, which takes five minutes and turns things you half-know into things you know. And carry it on the job, because the number you cannot remember is always the one somebody is waiting for.

A note on the words

Electrical vocabulary changes between countries more than almost any other part of AV. Ground in North America is earth in most other places. Line, live, hot and phase are all used for the conductor that carries current from the supply. A distro is a power distribution unit, a PD, a rack or a spider box. A GFCI in North America does much the same job as an RCD elsewhere. Cam-lok, twist-lock and powerCON are trade names used as ordinary words. And a show electrician may be the production electrician, the power tech, the sparky or the qualified person for the site.

None of that is worth arguing about. What matters is that you can say what a conductor, a device or a job does, because on power, a misunderstood word is a hazard rather than an embarrassment.

A note on safety

Electricity kills quietly and without warning. The current that can stop a heart is far smaller than the current that trips a breaker, and nothing about a live cable looks different from a dead one. The hazards on a show are rarely exotic. They are damaged cords, overloaded circuits, water, cable coiled under load, a ground pin broken off to make a plug fit, and somebody opening something that was not theirs to open.

Nothing in this book authorises you to do electrical work. When a task involves the supply side, the inside of distribution, a tie-in or wiring of any kind, it has left your hands and belongs to a qualified electrician. If you are ever unsure which side of that line a task is on, it is on the electrician's side.

Where this book sits

This book assumes you have read AV Fundamentals 101, or that you already know what is in it.

Experience counts instead. If you have time on crews where you have already plugged gear into show power, run cable, and know what a distro and a breaker are, start here.

If none of that is true yet, read AV Fundamentals 101 first.

What pairs with this

• AV Math Fundamentals — the arithmetic behind every load plan, practised

Where it leads

These are not steps in an order. Take whichever one fits.

• Signal Flow & System Architecture — because clean power and a clean signal path are half of the same fault-finding
• AV Troubleshooting Methodology — to find power faults as methodically as any other

Before You Begin

Volts, Amps & Watts

Three quantities describe electricity. Understanding them is the foundation of using power safely.

The three quantities

Electricity is described by three related quantities you must understand. Voltage (volts) is the electrical pressure — how hard the electricity is pushed (common mains voltages are around 120V or 230V depending on the country). Current (amps) is the rate of flow — how much electricity is actually flowing, which is what matters for whether a circuit is overloaded. Power (watts) is the rate at which energy is used — what a device consumes, and how power is usually rated. Volts, amps, watts: pressure, flow, and power used. Every electrical consideration in AV comes back to these three.

A simple, useful relationship ties them together: power (watts) equals voltage (volts) times current (amps). This means if you know a device's power in watts and the voltage, you can work out the current it draws in amps — which is exactly what you need to avoid overloading circuits (the subject of "Load & Avoiding Overloads"). You do not need deep electrical theory, but you do need these three quantities and their relationship, because they underpin safe power use in AV.

AC power and what gear needs

The power from wall outlets is AC (alternating current) mains power, and AV gear is designed to run on it (some gear uses power supplies that convert it to the low-voltage DC the electronics need internally, but you supply AC). Gear is rated for the power it needs — its voltage and its power draw in watts (or current in amps) — usually marked on the device. Knowing a device's power requirements is the starting point for powering it correctly and safely. Matching gear to the right power, and knowing how much it draws, is basic, essential AV practice.

Different countries use different mains voltages and outlet types, which matters when working internationally or with gear from elsewhere — using gear on the wrong voltage can damage it or be dangerous. The AV professional checks that gear is supplied the power it is rated for. Understanding that gear needs the correct AC power, rated by voltage and power draw, is the practical foundation for everything that follows about distributing power and not overloading it.

Resistance and Ohm's law

A fourth quantity sits underneath the three, and it explains most of what goes wrong with power on a show. Resistance is how much a material opposes the flow of current, measured in ohms. Copper has very little. Air, rubber and dry wood have a great deal. Your body sits somewhere in between, and it has far less when your skin is wet.

Ohm's law ties resistance to the other quantities: voltage equals current multiplied by resistance, written V = I × R. Rearranged, current equals voltage divided by resistance. Push the same voltage through less resistance and more current flows.

That single relationship explains three things a technician sees.

First, heat. Whenever current flows through resistance, some of the energy becomes heat. A thin conductor has more resistance than a thick one, so the same current heats it more, which is why cable size matters and why an undersized extension cord gets warm.

Second, bad connections. A loose or corroded connection is a small patch of high resistance in a conductor carrying a lot of current, and it heats up exactly there. A plug that is warm to the touch, a connector with brown discoloration around one pin, or a burning smell from a distro is almost always a bad connection heating under load. It gets worse, not better, and it is stopped and reported.

Third, shock. The voltage of the supply is fixed. What decides how much current flows through a person is their resistance, and wet skin, sweat and standing on a wet floor lower it dramatically. The same outlet that gives a dry hand a sharp jolt can drive a lethal current through a wet one.

You will not calculate resistance on a job. You will see its effects every week.

Power, worked

Watts equals volts times amps is the calculation you will use most, so it is worth doing until it is automatic. Rearranged, amps equals watts divided by volts.

A 1,200 watt device on a 120 volt supply draws 1,200 ÷ 120 = 10 amps. The same device on a 230 volt supply draws 1,200 ÷ 230, a little over 5 amps. The power the device uses is the same; the current it draws depends on the voltage it is fed. This is why the same rack of gear fits on fewer circuits in a country with 230 volt mains.

Going the other way, a 20 amp circuit at 120 volts can deliver 20 × 120 = 2,400 watts at its full rating. A 16 amp circuit at 230 volts can deliver 16 × 230 = 3,680 watts.

A useful shortcut on 120 volt supplies is to divide watts by 100 for a slightly high, safe estimate of amps: 1,200 watts is about 12 amps by the shortcut, 10 exactly. On 230 volt supplies, dividing watts by 200 gives the same kind of generous estimate. The shortcut is for a quick check in your head; the plan is done with the real voltage.

Energy is power over time. A 1,000 watt load running for one hour uses one kilowatt-hour. It matters for generator fuel and battery run time, which is how long a battery can supply a load before it is empty.

AC, DC and frequency

Mains power is alternating current, AC: the voltage swings positive and negative, reversing direction many times a second. Batteries and the electronics inside almost every AV device use direct current, DC, which flows one way at a steady voltage. The power supply inside a device, or the brick on its cable, converts one to the other.

How many times a second mains alternates is its frequency, measured in hertz. North America and parts of South America and Asia use 60 Hz. Europe, Africa, Australia, most of Asia and much of South America use 50 Hz. It rarely matters to modern equipment, most of which accepts either. It matters a great deal to anything that flickers — cameras filming lights, LED walls and fluorescent sources — and to older motors and transformers.

The number quoted for mains voltage, such as 120 or 230 volts, is not the peak of the swing. It is a kind of average called RMS that gives the same heating effect as that much DC. The actual peak is higher — about 170 volts on a 120 volt supply and about 325 on a 230 volt supply — which is one more reason mains is treated with respect.

Many devices have universal power supplies marked something like 100–240 V, 50/60 Hz, and adapt automatically. Some do not, and a device built for 120 volts plugged into 230 volts is destroyed in an instant, sometimes with fire. Reading the label is the check, every time the gear crosses a border.

Watts, volt-amps and inrush

Two practical complications make real power figures differ from the simple calculation, and both show up in AV.

The first is the difference between watts and volt-amps. For a simple load such as an old incandescent lamp, volts times amps gives the watts it uses. For many electronic loads, the current drawn from the supply does not line up neatly with the voltage, and volts times amps — the apparent power, measured in volt-amps, VA — is larger than the real power in watts. The ratio between them is the power factor. Modern gear with good power supplies has a power factor close to one, and the difference is small. It matters because UPS units and generators are rated in VA, or kVA, as well as watts, and the load must fit within both ratings.

The second is inrush current. When many devices switch on, their power supplies draw a brief surge of current, much larger than their steady draw, for a fraction of a second while they charge up. One laptop's inrush is nothing. A rack of amplifiers, a row of LED processors or a whole LED wall switched on at once can draw enough inrush to trip a breaker that would carry the running load comfortably. The fix is not a bigger breaker. It is switching loads on in stages, which is what power sequencers and the habit of powering up rack by rack are for.

Electricity is described by three quantities: voltage (volts — electrical pressure), current (amps — rate of flow, what determines overload), and power (watts — energy used, how gear is rated), related by watts = volts x amps (so you can find a device's amp draw from its watts and the voltage). AV gear runs on AC mains power, rated for the voltage and power it needs (marked on the device); supply gear the correct power, mind different countries' voltages, and know each device's draw.

The formulas

The only arithmetic a technician needs for power. V is volts, I is amps, R is ohms, P is watts.

Mains around the world

Typical nominal values. Always read the supply and the label.

On the job

A corporate launch in a hotel ballroom. The video team has set up four LED processors, two media servers and a rack of switching gear at the back of the room, all plugged into one 20 amp distro circuit that the hotel's electrician provided. Everything ran perfectly during setup, one device at a time.

At the end of the day the video engineer switches off the rack's main power strip to save the gear overnight. The next morning, the crew arrives, somebody flips the strip back on, and the breaker trips immediately. They reset it and it trips again. Somebody suggests the hotel has given them a faulty circuit.

You ask what is on the circuit and add it up from the labels. Four processors at 150 watts, two media servers at 750 watts, and the switching gear at about 300 watts: 2,400 watts on paper, which at 120 volts is exactly 20 amps. The circuit was already at its limit on the running load, and the moment everything started at once the inrush tipped it over.

You split the rack across two circuits, putting the media servers on their own, and power up in stages: switching gear first, then the processors, then each media server a few seconds apart. Nothing trips. Then you write the draw of each device on the power plan, so the next morning's power-up does not rely on anybody remembering.

How to do it

1. Find the label or nameplate on the device or its power supply.
2. Read the voltage range and frequency it accepts, and check the supply matches.
3. Read its power in watts, or its current in amps at a stated voltage.
4. If you have watts, divide by the actual supply voltage to get amps.
5. If the manufacturer publishes a typical and a maximum figure, note both.
6. Write the result in your notebook or the power plan against the device.
7. For racks and walls of many devices, note that they will draw inrush when switched on together.

What goes wrong

Practice it

Answer before checking.

The Supply — Phases and Conductors

Before you can plan how much a circuit can carry, you need to know what arrives at the distro and what each conductor in a cable is for. A household outlet hides almost all of it. Show power does not: it arrives as heavy cable with several colour-coded conductors, often as three phases, and the voltage you get depends on which conductors you connect between.

This chapter is what is on the other side of the distro — line, neutral and ground; single-phase, split-phase and three-phase supplies; how phases are balanced and why the neutral can carry more current than anyone expects; and the colour codes that change from country to country. It is knowledge for planning and for recognising what you are looking at. Every connection on the supply side belongs to a qualified electrician.

Line, neutral and ground

A normal circuit has three conductors, and each has a completely different job.

The line conductor, also called the hot, live or phase, carries current from the supply to the load. It is at mains voltage relative to the earth beneath your feet, and it is the one that kills.

The neutral conductor carries the current back from the load to the supply, completing the circuit. In normal operation it sits close to earth voltage, and in a fault it may not. It carries current, so it is treated with the same respect as a line.

The ground conductor, called the equipment grounding conductor in North American codes and the protective earth elsewhere, carries no current in normal operation at all. It connects the metal case of the equipment back to earth. It exists only for a fault: if a line conductor touches a metal case, the ground gives that fault current a low-resistance path home, a large current flows, and the breaker trips, instead of the case sitting at mains voltage waiting for a hand.

This is why a ground pin is never removed and a ground is never lifted on a power cable. The device works perfectly without one. It simply stops being safe, and nobody can tell until the moment it matters.

Single-phase, split-phase and three-phase

A single-phase supply is one line and a neutral, plus ground. It is what a normal outlet provides.

A split-phase supply, common in North American homes and small buildings, has two lines and a neutral. Each line is 120 volts to neutral, and the two lines are 240 volts to each other, which is how a North American house runs a 240 volt oven.

A three-phase supply has three lines, usually a neutral, and ground. The three lines each alternate the same way, but one third of a cycle apart from each other. Almost all show power arrives as three-phase, from a building's service or a generator, because it delivers far more power through the same size of cable.

The common three-phase arrangement for power distribution on shows is the wye, sometimes written star. In North America a wye service is usually 120/208 volts: each line is 120 volts to neutral, and 208 volts between any two lines. In Europe, the UK and many other places it is 230/400 volts: 230 to neutral, 400 between lines. A distro fed from a wye service gives ordinary single-phase outlets by connecting between one line and neutral, and different outlets on the same distro are fed from different lines.

Other arrangements exist, including delta supplies with no neutral and high-voltage services that are stepped down. What matters to a technician is not the theory but two facts: the voltage between two conductors depends on which two they are, and a distro's outlets are spread across different phases.

Balancing the phases

A three-phase distro divides its outlets between the three lines. Each line has its own capacity. If most of the load is plugged into outlets fed from one line, that line can be overloaded while the other two sit nearly idle, even though the distro as a whole is well within its rating.

So load is planned to balance the phases: roughly the same current on each line. A power plan lists which outlets are on which phase, often marked on the distro as X, Y and Z, A, B and C, L1, L2 and L3, or with coloured indicator lights, and assigns the gear so the totals come out close to each other.

Balancing also matters to the neutral. When three phases carry equal current from simple loads, their currents cancel in the shared neutral, and it carries very little. When they are unbalanced, the neutral carries the difference.

There is a catch that surprises people. Modern electronic loads — switch-mode power supplies in computers, LED fixtures, LED walls, amplifiers and processors — draw current in short bursts rather than smoothly, which creates harmonics, currents at multiples of the mains frequency. Some of those harmonics do not cancel in the neutral; they add. A three-phase system full of electronic loads, perfectly balanced, can put a neutral current as large as a phase current, or larger, on a conductor that was expected to carry almost nothing. That is why show power distribution is often built with a neutral as large as, or larger than, the line conductors, and why a technician never assumes the neutral is idle.

Colour codes change between countries

Wire colours tell a qualified person which conductor is which, and they are not the same everywhere. A technician who learned the colours in one country can be dangerously wrong in another.

In North America, fixed wiring uses black, red and blue for line conductors, white or grey for neutral, and green or bare copper for ground. The single-pole feeder connectors used on shows follow the same idea: green for ground, white for neutral, and black, red and blue for the three phases.

Under the international scheme used in Europe, the UK and many other countries, line conductors are brown, black and grey, neutral is blue, and protective earth is green and yellow striped. Older installations in some of those countries used other colours, including red for a line.

The dangerous overlap is plain to see. Black is a live line in both schemes. And blue is a line conductor on North American show feeder but the neutral under the international scheme. A colour on a conductor is information for a qualified person reading the right scheme; it is never a reason for anybody else to touch it.

Common supply arrangements

Conductor colours

On the job

An outdoor festival stage. The production electrician has set a large three-phase distro beside the stage and connected it to the generator. The video crew plugged the LED wall processors and the whole wall into the outlets nearest to their position, and the audio crew plugged the amplifier racks into the outlets nearest the stage wing.

During the first act, the electrician comes to front of house and asks who is responsible for the video power. The distro's meter shows one phase carrying nearly its full rating and the other two barely loaded. Every outlet the video crew used was on the same phase.

Nothing has tripped, and the video engineer points that out. The electrician's answer is that on a hot afternoon, with the wall at full brightness, it will — and that the neutral is carrying far more current than it should because the load is so uneven.

At the changeover the video crew moves half the LED wall's circuits to outlets on the second phase and the processors to the third, following the phase letters printed beside the outlets. The meter now shows three similar readings. The electrician writes the phase assignments on the power plan, and nothing trips for the rest of the weekend.

How to do it

1. Ask the show electrician for the power plan and the phase assignments.
2. Identify each outlet's phase from the markings on the distro.
3. Add up the planned current for each phase.
4. Assign heavy loads so each phase carries a similar total.
5. Keep equipment that must share a ground reference, such as the audio system, as the plan directs.
6. Plug in only to the outlets the plan names.
7. Ask the electrician to check the meter readings once the load is running.

What goes wrong

Practice it

Answer before checking.

Distributing Power

Power has to get from the supply to your gear, safely and in enough quantity.

From supply to gear

Power reaches your AV gear through a distribution chain: the mains supply (the building's or generator's power) feeds power distribution (which splits it into circuits), each circuit is protected by a breaker (which cuts power if too much current flows) and runs over cabling to outlets, into which your gear is plugged. Understanding this chain — supply, distribution, circuit/breaker, cable, gear — lets you see how power gets to your equipment and where the limits and protections are. It is the power equivalent of signal flow: trace from the source of power to your gear.

On AV jobs, especially larger events, you often work with power distribution equipment that takes a large supply and splits it into many outlets for the AV gear. You plug gear into this distributed power. Knowing how power is distributed — and that each circuit has a limit protected by a breaker — is what lets you power a system correctly without overloading anything. This understanding is essential for any AV setup beyond a couple of devices in a wall outlet.

Circuits and breakers

A circuit is one path of power from the distribution to outlets, and each circuit has a limit — a maximum current (in amps) it can safely carry, protected by a breaker (or fuse). If the gear on a circuit tries to draw more current than the limit, the breaker trips, cutting the power to protect the wiring from overheating. A tripped breaker is a safety feature doing its job — it means too much was drawn from that circuit. Understanding that each circuit has an amp limit, and that exceeding it trips the breaker (or worse, if unprotected, overheats wiring), is the key to powering AV safely.

This is why you cannot just plug unlimited gear into one circuit: every circuit has a capacity, and the total of what is plugged in must stay within it. Distributing your gear's power across circuits so none is overloaded is a core AV power skill — the subject of "Load & Avoiding Overloads". Knowing what a circuit and a breaker are, and that the breaker protects against drawing too much, is the foundation for managing power load safely.

The show electrician and the power plan

On any show larger than a few wall outlets, somebody is responsible for the power system as a whole. They may be the venue's electrician, a production electrician, the power company's technician or a qualified person the production has named, and in many places the rules for temporary event power require that such a person exists and is identified. Their name should be on the call sheet, and a technician who needs power should know who they are before plugging in anything larger than a laptop.

That person owns the power plan: what supplies the show, which distros are fed from it, what each circuit may carry, which department uses which outlets, and on which phase. The plan is written before load-in and updated as the show changes.

A technician's side of the plan is to tell the electrician what their department needs — a list of every device, its draw, and where it will be — and then to plug into the outlets the plan assigns. When the gear changes, the list changes, and the electrician is told before the new gear is plugged in, not after the breaker trips.

This relationship is the practical form of the firm line in this book. The electrician makes the supply safe and available. The technician uses it, within the limits the electrician set.

Distros, tie-ins and feeder

Show power usually starts at a connection point the venue provides, often called company switch: a disconnect panel with a large switched supply designed for touring productions to connect to. Outdoors, it starts at a generator.

From there, heavy feeder cable runs to the production's distribution. In North America the feeder is usually a set of single-core cables, one per conductor, with single-pole connectors widely called cam-lok. Elsewhere it is often a multi-core cable with large round industrial connectors. The feeder arrives at a distro: a box or rack with a main breaker and many smaller breakers, each protecting a circuit and its outlets, often with meters and phase indicator lights.

Connecting feeder to company switch or a generator is a tie-in, and it is electrical work. Single-pole connectors in particular are dangerous in the wrong hands, because they can be connected in the wrong order or to the wrong conductor. The rule used on shows is that the ground is connected first and disconnected last, then the neutral, then the phases, and the reverse when disconnecting, with the supply switched off throughout. A technician does not make or break these connections, does not open a distro, and does not reset a main breaker. They plug into the distro's outlets, and they call the electrician for everything upstream of that.

Smaller distribution — a power strip, a small distro box or a spider box with a handful of outlets — is where technicians work every day. Even there the same thinking applies: every outlet on it shares the circuit feeding it.

Generators

Outdoor events, broadcast trucks, festivals and remote locations run on generators, and a generator is a supply with its own rules.

A generator is rated in kVA and kW, and its real capacity depends on the load, the fuel, the altitude and the temperature. It is sized for the whole show with margin, including inrush. A generator run close to its limit can struggle when a large load switches on, and its voltage and frequency dip exactly when a lighting rig or a PA hits a big moment.

Voltage and frequency stability matter to AV. Some generators hold them tightly and are suitable for sensitive equipment; some vary as load changes. LED walls, cameras and digital audio equipment can all misbehave on unstable power.

Generator grounding and bonding — how the generator's neutral and frame are connected to earth — are decided by the qualified person responsible and are critical to the safety of everything connected. So are placement: exhaust away from people and air intakes, noise away from the audience and microphones, refuelling done safely, and the cable run from generator to distro protected.

Fuel matters too. A generator that runs out of fuel during a show is the most complete power failure there is. The power plan includes who refuels it and when.

Power reaches gear through a chain: mains supply → distribution (splits into circuits) → each circuit protected by a breaker → cable → outlets → your gear (the power version of signal flow). On larger jobs you use distribution equipment that splits a big supply into many outlets. Each circuit has an amp limit protected by a breaker that trips if too much current is drawn (a safety feature) — so you can't plug unlimited gear into one circuit; the total draw must stay within each circuit's capacity.

Who does what with show power

Single-pole feeder, the order a qualified person follows

• Supply switched off and confirmed.
• Connect ground first.
• Then neutral.
• Then the phases.
• Disconnect in exactly the reverse order, with ground last.

On the job

A touring corporate show arrives at a convention centre. The production has its own distro, and the venue has a company switch panel at the back of the hall. The venue's electrician is running late, and the stage manager is under pressure to get lights and screens up.

One of the crew says he has connected cam-lok before on another tour and offers to tie the distro in himself. The feeder is right there and the connectors are colour-coded.

You say no, and you say why in one sentence: a tie-in is electrical work, a single-pole connector made in the wrong order can put a phase on the ground, and neither of you is the qualified person for this building. The stage manager does not love it.

The crew spends the forty minutes building truss, running signal cable and preparing everything that does not need power. The electrician arrives, confirms the panel is off, makes the connections ground first, checks voltages on each phase at the distro, and hands over power with the phase assignments marked. The show loads in twenty minutes behind, and nobody is hurt, and nothing in the building has been damaged by a phase on a neutral.

How to do it

1. Find out who the show electrician or qualified person is, before load-in.
2. Send them a list of every device, its draw, and where it will be.
3. Get the power plan, with your outlets and their phases.
4. Wait for the electrician to hand over power; never connect feeder or open a distro.
5. Plug only into the outlets the plan assigns.
6. Tell the electrician before adding or changing gear.
7. Report any trip, warmth, smell or damage straight away.

What goes wrong

Practice it

Answer before checking.

Cable, Connectors and Voltage Drop

A breaker protects a cable, but only if the cable is the right size for the breaker, used the right way, and in good condition. Most of the power incidents on a show involve cable: a cord too thin for its load, a reel left coiled under a heavy load, a connector used above its rating, a damaged jacket, or a long run delivering less voltage than the gear needs.

This chapter covers what a technician runs, plugs and inspects every day: conductor size and what it can carry, the cord types and what they are for, the connector families and their limits, voltage drop on long runs, and how cable is run, protected and inspected.

Conductor size and ampacity

The current a conductor can carry without overheating is its ampacity, and it depends mostly on the conductor's size. Bigger conductors have lower resistance, heat less and carry more.

In North America conductor size is given in AWG, American Wire Gauge, where a smaller number is a thicker conductor: 16 AWG is thinner than 12 AWG, and 4/0 feeder is very thick indeed. Elsewhere it is given in square millimetres of cross section, where a larger number is thicker: 1.5 mm² is thinner than 2.5 mm².

A cord must be rated for at least the current of the breaker protecting it. A 20 amp circuit needs cord that can carry 20 amps; a light 16 AWG extension lead rated for less, plugged into that circuit and loaded, can overheat long before the breaker notices anything wrong. The breaker was chosen for the building's wiring, not for whatever was plugged into it.

Ampacity also falls when heat cannot escape: when a cable is bundled tightly with others, run through insulation, left in direct sun, or coiled. The rated figure assumes the cable can cool.

Coiled cable heats itself

A cable that carries current makes a little heat along its whole length. Laid out straight, that heat escapes into the air. Coiled tightly, or left wound on a reel, each turn is surrounded by other warm turns, the heat cannot escape, and the temperature climbs. Under a heavy load, a coiled cable can soften its own insulation and melt, and it looks perfectly tidy while it does.

The rules follow directly. A cable reel is fully unwound before a significant load is connected to it. Excess length on a heavy power cable is laid out in a loose, open figure-of-eight or long loops, not a tight coil. And a neat coil of feeder hidden under a stage with the full show running through it is exactly the kind of thing to look for on a walk round.

Cord types and where they may be used

Flexible cord is built for different uses and marked on its jacket. Portable cord for show power in North America is commonly type SO, SOOW or similar: a hard-service, oil-resistant rubber jacket, with W indicating it is rated for wet locations. Lighter cords, such as SJ types, are junior service with thinner jackets. Other countries use their own designations, such as H07RN-F for heavy-duty rubber cable in Europe.

What matters is that the cord's jacket is suited to how it is used: hard-service cord for floors that people walk on and cases roll over, outdoor-rated cord outdoors, and nothing lighter than the load and location need. Household extension cords, flat cords and thin leads from a hardware store are not show cable, whatever the rating printed on the packet.

Connector families

The connector on a cable tells you, before anyone reads a label, what voltage and current that line is built for — and some connectors carry rules about how they are used.

Edison or household plugs, NEMA 5-15 and 5-20 in North America, are the everyday 15 and 20 amp, 120 volt connectors. The 20 amp version has one blade turned sideways.

Twist-lock connectors, such as NEMA L5-20 and L5-30, lock with a turn so they cannot be pulled out, and are common on show distribution. L21-30 carries three phases, neutral and ground in one connector.

IEC connectors are the familiar detachable leads on the back of equipment: C13 and C14 for most devices, and the larger C19 and C20 for high-current gear.

powerCON is a locking connector common on audio and lighting equipment. The original blue and grey version must not be connected or disconnected under load; the newer TRUE1 version is designed to be. Knowing which one you are holding matters.

CEE, or IEC 60309, industrial connectors are the round colour-coded connectors used for show power in much of the world — blue for 230 volt single-phase, red for 400 volt three-phase — in 16, 32, 63 amp and larger sizes.

Socapex is a 19-pin multi-circuit connector carrying six separate circuits in one cable, most common in lighting.

And single-pole connectors, the cam-lok type, carry feeder one conductor at a time, and belong to the electrician.

Two rules cover all of them. Never force a connector, modify one to fit, or use an adaptor that lets a higher-current supply feed a lower-rated connector or cable. And never break the ground connection to make a plug fit.

Voltage drop on long runs

Every conductor has some resistance, so current flowing along a cable loses a little voltage along the way. On a short run it is negligible. On a long run of thin cable carrying a heavy load it is not: the distro reads 120 volts, and the gear at the end of eighty metres of light cable receives noticeably less.

The drop grows with the current, the length of the run and the thinness of the conductor. Double the length and the drop doubles; double the current and the drop doubles; use a thicker conductor and it falls.

Gear fed with low voltage misbehaves in ways that look like other faults. Power supplies work harder and run hotter, amplifiers lose headroom, LED products reboot or flicker, motors stall, and devices restart when a large load switches on nearby.

The remedy is planning: put distribution close to the load and run short, and use heavier cable for long runs rather than daisy-chaining light cords. On a large site, the electrician calculates voltage drop for long feeder runs as part of the design. A technician's contribution is not to create long thin runs to save walking, and to recognise the symptoms.

Running, protecting and inspecting cable

Cable on a show floor is a trip hazard, a crush hazard and, if it is damaged, a shock and fire hazard, all at once.

Power cable is run along walls and out of walkways wherever possible. Where it must cross a path used by people, it is covered with cable ramps or cable protectors, and where vehicles or rolling cases cross, with protectors rated for that load. It is not run through doorways that close on it, under carpets where damage cannot be seen, or across fire exits. It is kept apart from signal cable where possible, and crosses it at right angles where it cannot.

Every power cable is inspected every time it is used. Before plugging in, look along the jacket and at both ends: cuts, crushing, exposed inner conductors, repairs with tape, missing or bent pins, a broken ground pin, cracked housings, strain reliefs pulled out of the connector, discoloration or a burning smell. A cable with any of these is taken out of service, tagged with what is wrong, and put where nobody will use it.

Many places also require periodic formal inspection and testing of portable equipment by a competent person — called PAT testing in the UK, and continuity and ground testing or assured equipment grounding programmes elsewhere — with a record kept and a label on the item. A technician's daily visual check comes on top of that, not instead of it.

Conductor size and typical capacity

Indicative only. Real ampacity depends on cord type, temperature rating, bundling and the code that applies. The rating marked on the cable and the electrician's plan are the authority.

Connectors you will meet

Voltage drop, as a relationship

The shape of the problem, not a design calculation.

Voltage drop increases with

• More current.
• A longer run.
• A thinner conductor.
• Poor or loose connections along the way.

Inspect every cable, every time

• Jacket cuts, crushing or exposed conductors.
• Tape repairs.
• Bent, missing or loose pins, and the ground pin present.
• Cracked housings and pulled-out strain reliefs.
• Discoloration, melting or a burning smell.

On the job

An outdoor corporate dinner under a marquee. The audio crew needs power for a small amplifier rack at the far end of the marquee, about seventy metres from the only distro. Somebody has joined four household extension cords end to end to reach it, and wound the leftover length of the last one into a neat coil behind the rack.

During the speeches the amplifiers start cutting in and out, and the coil behind the rack is warm to the touch.

There are four faults in one cable run. Household cords are too light for an amplifier rack. Four joints add four connections, each a small resistance. Seventy metres of thin cable carrying a heavy load drops the voltage enough to make the amplifiers' protection trip. And the coil is heating itself.

You ask the host for a five-minute pause in the music, switch off the amplifiers, and unplug the run. The show electrician runs a single length of heavy outdoor cord from a spare outlet on a distro circuit he moves closer, laid out along the marquee edge under a cable protector where it crosses the service path. The amplifiers come back up and hold for the rest of the night. The household cords go back in the van with a note to the crew chief not to bring them again.

How to do it

1. Choose a cable rated for at least the circuit's breaker current and suited to the location.
2. Inspect the whole jacket and both connectors before using it.
3. Plan the route along walls and away from walkways, doors and fire exits.
4. Unwind any reel completely before connecting a significant load.
5. Lay excess in open loops or a figure-of-eight, never a tight coil.
6. Cover every walkway crossing with a suitable cable protector.
7. Avoid chaining cords; use one cable of the right size and length.
8. Keep power apart from signal cable, crossing at right angles where needed.

What goes wrong

Practice it

Answer before checking.

Load & Avoiding Overloads

The everyday electrical skill: don't ask a circuit for more than it can give.

Calculating load

The most important everyday electrical skill in AV is avoiding overloads — making sure the gear on a circuit does not draw more current than the circuit can supply. To do this, you work out the load: the total current (in amps) that the gear plugged into a circuit will draw. Using the relationship from "Volts, Amps & Watts" (watts = volts x amps), you can find each device's current draw from its power rating and the voltage, then add up the draws of everything on the circuit. That total must stay within the circuit's amp limit, with margin to spare. This simple calculation — total the draw, compare to the limit — is what prevents overloads.

Doing this is basic professional practice whenever you power more than a little gear. You know (or look up) each device's power, work out the current, add it up, and make sure it is safely under the circuit's rating. Leaving margin matters — running a circuit right at its limit is asking for trouble, especially with gear whose draw can spike. The AV professional plans power load deliberately rather than plugging in and hoping the breaker holds.

Distributing load and avoiding problems

When you have more gear than one circuit can carry, you distribute the load across multiple circuits so none is overloaded — spreading the gear so each circuit stays within its limit. This is why understanding distribution ("Distributing Power") and load (this chapter) go together: you arrange your gear across the available power so the total on each circuit is safe. Planning this in advance — knowing your gear's total draw and the available circuits, and dividing one across the other — is how a larger AV system is powered reliably without tripping breakers mid-show.

Overloading causes real problems: a tripped breaker kills power to your gear (potentially mid-event), and overloaded or undersized wiring can overheat and become a fire hazard — which is why circuits are protected and why staying within limits matters for safety, not just convenience. The AV professional avoids these by calculating and distributing load properly. This everyday discipline — know the draw, know the limits, distribute and stay under with margin — is the practical core of using power well in AV.

Continuous load and the 80 percent rule

The original advice in this chapter was to stay under a circuit's limit with margin. On shows there is a specific reason and, in many places, a specific rule.

A breaker's rating is the current it carries indefinitely under test conditions. In real installations, a load that runs for hours heats the breaker, the wiring and the connections, and a circuit run at its full rating for a whole show will often trip, or cook the weakest connection, even though the calculation said it fitted.

So electrical codes treat a continuous load — in the North American code, a load expected to run at its maximum for three hours or more — differently. The continuous load on a standard breaker is limited to 80 per cent of its rating. A 20 amp circuit carries a continuous load of 16 amps; at 120 volts that is 1,920 watts, not 2,400. A 15 amp circuit carries 12 amps, 1,440 watts.

Almost everything on a show is continuous: the LED wall, the amplifiers, the processors and the lighting run from doors to the end of the night. Planning every circuit to 80 per cent is the practical rule, whatever country you are in, and it also leaves the headroom for inrush and for a hot afternoon.

Real power figures — nameplate, typical, maximum and 1/8 power

The watts on a device's nameplate are often not what it draws on a show, and different kinds of equipment publish their draw in different ways. Planning on the wrong figure either wastes circuits or trips them.

A nameplate or label rating is usually the maximum the power supply is built for, or a figure for safety approval. It is a safe, generous number to plan with when nothing else is available.

LED walls and many LED fixtures publish a typical draw and a maximum draw. Typical is the draw with ordinary video content; maximum is full white at full brightness. A wall showing a mostly dark set during a keynote draws a fraction of its maximum. A wall showing a white slide, or an entire bright colour at a product reveal, draws its maximum, and power is planned for the maximum the show will ever display.

Moving lights draw most when their lamp strikes or their motors all move at once, and publish a maximum.

Amplifiers are different again. An amplifier's maximum output power is only drawn briefly on peaks, and manufacturers usually publish current draw at one-eighth power with pink noise, which represents loud, typical programme material, alongside figures at one-third power for very heavily compressed content. A sound system is usually planned on the one-eighth or one-third figure the manufacturer gives for the kind of show, not the huge number that would come from multiplying out the amplifier's peak output.

When a manufacturer gives no figure, the label is used, and when two figures conflict, the higher is used until the gear can be measured on the show.

Writing a power plan

A power plan is the load calculation written down in a form everybody can use. It does not need special software. It needs to be accurate, current and in the hands of the people plugging in.

A simple plan is a table. Each row is a device or a group of identical devices, with its location, its draw in amps at the real voltage, which circuit it is plugged into and which phase that circuit is on. At the bottom, each circuit's total is compared with its 80 per cent limit, and each phase's total with its capacity.

Writing the plan finds problems on paper that would otherwise be found at doors. It shows a circuit carrying the LED processors and the media servers going over its limit. It shows one phase with three times the load of the others. It shows that the lighting console and the audio console are on the same circuit as the catering urn.

The plan is also how departments share power. The show electrician gathers each department's list, assigns circuits, and returns the plan. When a department adds a device, it is added to the plan and to a circuit with room, before it is plugged in.

Metering what is really drawn

A power plan is a prediction. A meter is the truth.

Many distros have built-in meters showing current on each phase and sometimes voltage. Reading them once the show is running — and again at the busiest moment of the show, when the wall is brightest and the PA is loudest — shows whether the plan was right. A reading close to 80 per cent of a phase's rating is a warning to act on before the show gets louder or brighter.

A clamp meter measures current by clamping around a single conductor, without any electrical connection. It is how an electrician checks the current on a feeder or a circuit, and it must be clamped around one conductor, not a whole cable, because the currents in the line and neutral of a cord cancel and read zero. Special split adaptors let it be used on a cord safely. Using a clamp meter on feeder or inside a distro is the qualified person's job; reading a distro's own meter is everyone's.

When the readings and the plan disagree, the plan is updated to match what was measured, and anything close to its limit is moved.

The key everyday skill is avoiding overloads: calculate the load (total current the gear draws) using watts = volts x amps to find each device's amps, add them up, and keep the total safely under the circuit's amp limit with margin. When gear exceeds one circuit, distribute the load across multiple circuits so none is overloaded. Overloading trips breakers (killing power mid-event) and can overheat wiring (a fire hazard) — so calculating and distributing load is safety, not just convenience.

Circuit capacity at 80 percent continuous

Which power figure to plan with

A power plan, worked

A small general session on 20 A, 120 V circuits, planned to 16 A continuous.

Phase totals

• A — 21.5 A
• B — 25.5 A
• C — 20.0 A

On the job

A product reveal in a convention hall. The video team planned the LED wall's power on the typical figure from the manufacturer, which put two circuits of wall panels comfortably under their limits at rehearsal, where the content was a dark branded background.

At the reveal, the content cuts to a full-screen white logo, the wall hits full brightness, and within seconds both wall circuits trip. The stage goes half dark for twenty seconds in front of a thousand guests while the electrician resets them.

Afterwards the numbers are simple. The panels' maximum draw is almost three times their typical draw, and full white is maximum. On the typical figure, each circuit was at 7 amps. At maximum, each was at over 19 amps, above even the 20 amp rating.

For the second night, the wall is replanned on its maximum, which needs four circuits instead of two, spread across all three phases. The electrician reads the distro meter during the reveal rehearsal with the white logo on the wall, and the highest phase reads well under its limit. The reveal runs with the stage fully lit.

How to do it

1. List every device and how many of each.
2. Find the right figure for each — label, maximum, or amplifier 1/8 or 1/3 power.
3. Convert every figure to amps at the actual supply voltage.
4. Group devices onto circuits so each stays at or under 80 per cent of its rating.
5. Spread circuits across phases so the phase totals are close.
6. Write it as a table, with circuit, phase, gear, amps and limit.
7. Give it to the show electrician, and plug in only as planned.
8. Read the meters at the busiest moment of the show and update the plan.

What goes wrong

Practice it

Answer before checking.

Grounding, GFCI and Protection

Three different devices protect a show's power, and they protect against three different things. A breaker or fuse protects the wiring from overheating. The ground protects against a metal case becoming live. A GFCI or RCD protects a person from a shock. People who confuse them believe they are protected when they are not — most dangerously, that a breaker will save somebody who touches a live conductor. It will not.

This chapter explains each protection, what it can and cannot do, and the one thing a technician must never do to any of them.

Breakers and fuses protect the wiring

A breaker or fuse is overcurrent protection. It disconnects a circuit when the current through it exceeds its rating for long enough: a fuse by melting a thin link, a breaker by tripping a switch that can be reset.

Both respond to two kinds of excess. An overload — somewhat more current than the rating, for a while — heats the protection slowly, and it trips after seconds or minutes, which is why an overloaded circuit can run for a time before it goes. A short circuit — a fault that lets a huge current flow — trips it almost instantly.

What a breaker is sized for is the wiring it feeds. A 20 amp breaker exists so that the wiring behind it never carries enough current to overheat and start a fire. It is not sized for people. The current that trips a 20 amp breaker is two hundred to four hundred times more than the current that can stop a human heart. A person touching a live conductor and ground does not trip a breaker; they are simply a load on it.

A tripped breaker is information. It means the circuit was asked for more than it could safely carry, or there is a fault. Resetting it repeatedly without finding out why is how cables and connectors are damaged. On a show, a technician reports a trip to the electrician, reduces the load or finds the faulty device, and, where the plan allows technicians to reset outlet breakers, resets once. A breaker that trips again straight away with the load reduced has found a fault, and it stays off.

Grounding and bonding

Grounding connects the metal parts of equipment to earth through the ground conductor. Bonding connects metal parts to each other, so they sit at the same voltage. Together they make sure that exposed metal a person might touch cannot sit at a dangerous voltage.

Here is how it saves a life. Inside a device, a line conductor comes loose and touches the metal case. If the case is grounded, a large fault current flows from the line, through the case, down the ground conductor and home, and the breaker trips in a fraction of a second. The case never sits at mains voltage long enough to matter.

Now remove the ground. The same fault happens. No current flows, because there is no path, so the breaker does not trip. The device carries on working. Its metal case now sits at full mains voltage, and it stays that way silently until a person touches it while touching anything else grounded — a microphone stand, a lighting truss, a console, a wet floor. The person becomes the ground path.

That is why the ground pin is never removed, a ground adaptor that defeats the ground is never used, and a ground is never lifted on a power connection to cure hum. Hum is a signal problem, solved in the signal path. A lifted ground is a lethal problem, invisible until it kills somebody.

Bonding explains a related rule on stages. Metal structures near equipment — truss carrying lighting, metal staging, a scenic frame — may be bonded to ground by the electrician so that a fault cannot leave them at a different voltage from the equipment. That work, and any decision about how the supply's neutral and ground are connected, belongs to the qualified person.

GFCI and RCD — protection for people

A ground fault circuit interrupter, GFCI, in North America, and a residual current device, RCD, in most other countries, protect people from shock. They work on a completely different principle from a breaker.

In a healthy circuit, every bit of current that goes out on the line conductor comes back on the neutral. The device continuously compares the two. If some current is going out and not coming back, it must be leaking somewhere else — through damaged insulation to ground, through water, or through a person. When that difference exceeds a small threshold, the device disconnects the circuit in a fraction of a second.

The thresholds are tiny compared to a breaker's. A Class A GFCI, the kind for personnel protection in North America, trips at around 5 milliamps. RCDs for personal protection elsewhere usually trip at 30 milliamps. Those currents can still be felt, but disconnected fast enough they are very unlikely to cause lasting harm.

GFCI and RCD protection is required in more and more locations: outdoors, near water, in wet or damp locations, on temporary power and on construction sites, and the entertainment industry has its own recommended practice for where Class A GFCIs belong on shows. Where the rules or the electrician put them, they stay.

Two practical facts matter to AV. First, they are tested: most have a test button, which is pressed before use to confirm the device trips, and one that does not trip is out of service. Second, some large AV loads — long runs of cable, big racks of switch-mode power supplies, LED walls — have small normal leakage currents that add up, and a GFCI feeding many of them can trip without any fault. The answer is to share the load across more protected circuits, as the electrician decides. It is never to remove or bypass the protection.

Surge protection

A surge is a very short spike in voltage, far above normal. Lightning striking near power lines causes the largest; large motors and loads switching on and off, generators starting and faults on the supply cause many smaller ones.

Surges rarely hurt people, but they damage electronics, sometimes instantly and sometimes by weakening components that fail days later. A surge protector limits these spikes by diverting the excess energy away from the equipment.

Surge protection comes built into many power conditioners and good power strips, and at larger scale it is installed at the distribution by electricians. It wears out: a protector that has absorbed large surges may stop protecting while still passing power, and many have an indicator light showing whether protection is still active.

Surge protection is not a UPS, and a UPS is not always a surge protector. The clean power chapter explains the difference.

The protections, and the job each does

Never

• Remove a ground pin.
• Use an adaptor that defeats the ground.
• Lift a ground on a power connection to cure hum.
• Bypass, tape down or remove a GFCI or RCD.
• Keep resetting a breaker that trips again straight away.

On the job

A wedding reception on a lawn beside a lake. The DJ's equipment and two powered loudspeakers are plugged into a GFCI-protected outdoor distro the venue's electrician provided. Early in the evening the GFCI trips, and the music stops.

The DJ resets it. It holds for ten minutes and trips again. A guest who says he is handy suggests plugging the DJ into the extension cord running from the kitchen instead, which has no GFCI and has not tripped once.

You say no to that, and explain in one sentence: the GFCI is tripping because current is leaking somewhere, and the kitchen cord would simply stop telling anyone about it, next to a lake.

You switch off and unplug everything on the circuit, then reconnect one item at a time, resetting the GFCI after each. It holds with the DJ console and one loudspeaker. It trips as soon as the second loudspeaker's power cable is connected. That cable runs across the lawn, and where it passes through a low spot the connector between two cords is sitting in a puddle from the afternoon's sprinklers.

The wet connection goes out of service. The electrician runs a single dry length, raised off the ground on a cable tray through the low spot. The GFCI holds for the rest of the night, and it was the only thing between a wet connector and the guests walking across that lawn in the dark.

How to do it

1. Do not reset straight away; note what happened just before the trip.
2. Tell the show electrician.
3. Reduce the load or disconnect the likely device.
4. For a breaker, reset once if the plan allows technicians to; if it trips again, leave it off.
5. For a GFCI or RCD, switch off and disconnect everything on the circuit, then reconnect one item at a time.
6. When the faulty item or cable is found, tag it out of service.
7. Never move the load to an unprotected supply to stop the trips.

What goes wrong

Practice it

Answer before checking.

Electrical Safety

Electricity can kill. Safe practice and knowing your limits are non-negotiable.

Core electrical safety

Electricity can injure or kill, so electrical safety is essential and non-negotiable. The core practices: treat all power as live and dangerous until proven otherwise; use only undamaged cables and proper connectors (a damaged power cable is a serious hazard); keep electricity away from water (a critical danger at outdoor and wet events — water and electricity together can be lethal); do not overload circuits ("Load & Avoiding Overloads"); and never bypass or defeat electrical safety devices (breakers, grounding) — they are there to protect lives. If anything seems wrong — a warm connector, a burning smell, a tingle, a damaged cable — stop and report it rather than continuing. These practices keep you and others safe around the power AV uses.

Grounding (earthing) is a key safety concept: a safety path that protects against electric shock if a fault occurs, which is why many plugs have a ground pin and why you never defeat it. You do not need to understand grounding deeply, but you must respect it — never remove or bypass a ground, because it is a life-safety feature. Safe electrical practice is largely about respecting these protections, handling power carefully, and never taking shortcuts with electricity.

Knowing your limit: use vs electrical work

There is a firm, critical line between using power safely (normal AV work) and doing electrical work (for qualified electricians). Using power — plugging in gear, running power cables, using distribution as trained, managing load — is normal AV work you do safely with this knowledge. Electrical work — wiring, modifying mains power, connecting into the electrical supply, anything inside the permanent electrical system — requires a qualified, licensed electrician and is often legally restricted. The AV professional uses power safely and calls a qualified electrician for anything beyond that, never improvising or doing electrical work untrained. This boundary is absolute because the consequences of getting electrical work wrong are lethal.

Knowing and respecting this limit is exactly the kind of professional judgement safety training emphasises: do the AV power work you are trained for, and get the qualified person for actual electrical work. There is no acceptable reason — time, cost, confidence — to cross into electrical work you are not qualified for. The aware professional uses electricity confidently and safely within their role, recognises when a task is electrical work, and defers it to an electrician. That combination — competent safe power use plus respect for the limit — is what this book builds.

Electricity can kill, so safety is non-negotiable: treat all power as live, use undamaged cables/connectors, keep electricity away from water, don't overload circuits, never bypass safety devices (breakers, grounding), and stop/report anything wrong. Respect grounding as a life-safety feature — never defeat it. There's a firm line: using power (plugging in, running cable, managing load) is normal AV work, but wiring and mains electrical work are for qualified electricians — never do electrical work you're not trained and authorised for.

What electric shock does to the body

The reason electrical safety rules can seem excessive is that the danger is invisible and the numbers are unintuitive. A circuit breaker trips at tens of amps. The human body is harmed by thousandths of an amp.

Current, not voltage, is what does the damage, and the voltage and your body's resistance decide how much flows. Roughly: around one milliamp through the body can be felt as a tingle. Somewhere around ten milliamps, the muscles of the hand clamp shut and a person may be unable to let go of what they are holding, which keeps them in contact. Somewhere from fifty to a hundred milliamps passing across the heart can disturb its rhythm and stop it pumping, which is fatal without rapid help. The exact figures vary with the person, the path the current takes and how long it flows, and mains voltage can easily drive these currents through a person with wet hands.

The path matters. Current from one hand to the other, or from a hand to the feet, passes across the chest and the heart. This is why a shock from a microphone and grounded guitar strings, or from a live case while leaning on a truss, is so dangerous.

Shock also causes secondary injuries: a fall from a ladder, a platform or a stage edge caused by the jolt, and burns where the current enters and leaves the body, which can be far deeper than they look.

Anybody who has received a significant shock should get medical attention, even if they feel fine, because heart rhythm effects can appear later.

Arc flash

An arc flash is an explosion of electrical energy through the air when a fault occurs between conductors, or between a conductor and ground, in equipment carrying a lot of power. For a moment the arc is hotter than the surface of the sun. It vaporises metal, throws molten droplets and a pressure wave, and causes severe burns and blindness to people nearby who never touched anything.

Arc flash is most likely where large amounts of power are concentrated: distribution panels, company switch, feeder connections, generators and large distros — exactly the places technicians are told to leave to electricians. It is often triggered by work on live equipment: a dropped tool, a connection made under load, a cover removed from a live panel.

This is why qualified electricians work on this equipment only after making it electrically safe wherever possible, wear arc-rated protective clothing chosen for the hazard when they cannot, and keep other people back behind approach boundaries while they work. For a technician the lesson is simple. When a panel, company switch or distro is open, or an electrician is working on feeder, stay back beyond the boundary they set, and never stand and watch at arm's length.

Qualified persons, lockout and tagout

Workplace electrical safety standards divide people into two groups. A qualified person has the training and knowledge to recognise and avoid the hazards of particular electrical equipment and work, and has shown they can. Everybody else is unqualified for that work, however experienced they are at other things. The firm line in this book is the same idea: a technician using power is not doing work that requires qualification; anything that exposes a person to live parts does.

The standard method for making equipment safe to work on is to create an electrically safe work condition: identify every source of supply, switch it off, verify with a proper tester that it is actually dead, and lock it off so nobody can switch it back on. The lock is part of lockout and tagout: a padlock on the disconnect, owned by the person working, with a tag saying who put it there and why. Only that person removes it.

A technician will see lockout and tagout on shows and in venues. The rules for a technician are absolute: never remove somebody else's lock or tag, never switch on a disconnect that has a lock or tag on it or that somebody has said is off for work, and never assume equipment is dead because a switch is off. If you are asked to switch something back on and there is a tag on it, the answer is to find the person whose name is on the tag.

Simple testers a technician may use

Two simple testers are useful to a technician, and neither involves opening anything.

A plug-in outlet tester is plugged into an ordinary outlet and shows, with a pattern of lights, whether the outlet is correctly wired: whether ground is present, and whether line and neutral are reversed. Many include a button to test a GFCI. It is a quick way to check an unfamiliar outlet before plugging in audio equipment, and an outlet showing any fault is reported and not used.

A non-contact voltage tester is a pen-shaped device that beeps or lights near a live conductor, without touching it. It is useful as a warning — for instance, to confirm that a cable you are about to handle is not unexpectedly live, or that a metal case is not energised. It has limits: it can miss a live conductor in shielded cable or when its battery is low, and it can react to nearby cables. It is a warning device only, never the proof that something is dead before work, which requires a proper tester and a qualified person.

Multimeters and clamp meters are measuring instruments with their own training and ratings. A technician may use a multimeter to check continuity on an unplugged signal or power cable. Measuring voltage on a live supply, or current on feeder, is for the qualified person.

Water, weather and outdoor power

Water lowers the body's resistance, conducts along surfaces and into connectors, and turns small leakage into dangerous leakage. Outdoor and wet events therefore change everything about power.

Connectors are kept off the ground, raised on blocks, trays or cable bridges, and protected from rain with purpose-made covers — not plastic bags, which trap condensation. Distros are rated for outdoor use and positioned where water will not pool. All outdoor circuits are GFCI or RCD protected. Cable is outdoor-rated. Nobody handles power connections with wet hands or while standing in water.

Weather is watched. A production outdoors has a plan for rain that includes power: which equipment is covered, which is switched off, and who decides. Lightning has its own rules: when lightning is close, work at height stops, crews leave metal structures such as stages and truss, and exposed electrical equipment may be powered down on the production manager's call. Many productions use a distance or time rule after the last lightning before work resumes.

Batteries

A growing share of AV equipment runs on large lithium batteries: wireless microphones and in-ear packs, camera batteries, V-mount and Gold Mount packs, battery-powered LED fixtures, and intercom beltpacks. A lithium battery stores a lot of energy in a small space, and when it fails, it can overheat, vent flammable gas and burn fiercely in a way that is very hard to put out.

Most battery fires come from damage, poor charging or short circuits. A battery that has been dropped, crushed, punctured, swollen, or has become hot to the touch is taken out of use and isolated, away from anything flammable. Batteries are charged on the charger designed for them, on a non-flammable surface, and not left charging unattended in a hotel room or a road case. Loose batteries are kept with their terminals covered, because keys, coins or a stray cable across the terminals is a short circuit.

Transport has rules too. Airlines limit the size of lithium batteries that may be carried and generally require spare batteries to travel in the cabin rather than in checked baggage, with terminals protected. Large packs may need approval or may be forbidden. Checking the rules before a flying job saves having a production's camera batteries confiscated at the airport.

Current through the body

Approximate and variable. The point is how little current it takes.

Around live equipment

The rules that keep a technician safe near live power, and what to do if somebody is shocked.

A technician never

• Opens a distro, panel or company switch.
• Makes or breaks a tie-in.
• Removes another person's lock or tag.
• Switches on anything tagged or said to be off for work.
• Stands close while an electrician works on live power.
• Uses a non-contact tester as proof that something is dead.

When somebody is being shocked

• Do not touch them while they are in contact with the source.
• Switch off the supply if it can be done safely and quickly.
• Otherwise separate them with something dry and non-conductive.
• Call for help and emergency services.
• Start first aid and CPR if trained and needed; use a defibrillator if available.

On the job

A theatre get-in. The venue electrician has locked off a distribution panel backstage to replace a damaged outlet, with a padlock and a tag with her name on it, and gone to the store for a part.

The lighting programmer needs the panel's circuit to power the console and asks you to switch it back on — "she'll only be ten minutes, and the outlet she's fixing isn't the one we need".

You explain that the lock and tag are hers, that she may have exposed live parts she is relying on staying dead, and that you cannot know which circuits are safe. The only person who removes that lock is the person whose name is on the tag.

You call her on the radio. She is back in five minutes, says the damaged outlet's wiring is exposed on a circuit fed from that panel, finishes the repair, removes her lock, and switches it on. The console is up fifteen minutes later than the programmer wanted, and nobody touched a live outlet with a screwdriver in their hand.

How to do it

1. Look at the outlet for damage, scorching or looseness.
2. Plug in an outlet tester and read the lights against its legend.
3. Test the GFCI or RCD with its test button where there is one, and reset it.
4. Inspect the cord you will use along its whole length.
5. Confirm the outlet's circuit is the one the power plan assigns.
6. Report any fault and use nothing that fails.

What goes wrong

Practice it

Answer before checking.

Clean Power & Applying It

Reliable AV power is safe, sufficient, and clean — and used within your limits.

Clean power and reliability

Beyond safety and load, AV cares about clean, reliable power, because power problems can disrupt AV gear. Electrical noise on the power can introduce hum or interference into audio and video (which is why power and signal cabling are kept apart, as the chapter on cable explains). Power dips, surges, or interruptions can disrupt or damage sensitive AV gear. For these reasons, AV setups sometimes use power conditioning (to clean the power) or backup power like a UPS (to keep critical gear running through an interruption) for important systems. Understanding that AV wants not just enough power but clean, stable power is part of powering systems well.

This is the same reliability thinking every AV job asks of you: for critical AV, you protect against power problems just as you protect against other failures — clean power, stable supply, and backup where it matters. The AV professional considers power quality and reliability, not just quantity, when powering an important system. Clean, stable, sufficient power is the foundation a reliable AV system stands on.

Applying electrical knowledge well

Pulling it together, applying electrical knowledge in AV means: knowing your gear's power needs, distributing power correctly across circuits without overloading, working safely around electricity, ensuring clean and reliable power for important systems, and — crucially — staying firmly within the line of safe power use, calling a qualified electrician for any actual electrical work. This combination lets you power AV systems correctly and safely, which is foundational to every AV setup. It is the practical electrical competence every AV professional needs.

This knowledge is part of the broader foundation (alongside acoustics, AV math, codes, and documentation) that underpins professional AV and certifications like the CTS. Deeper electrical expertise belongs to electricians; what every AV professional needs is exactly what this book provides — the understanding to use power safely, distribute it correctly, avoid overloads, recognise hazards, and know their limit. Master it, and you will power AV systems competently and safely for the rest of your career, while always respecting the line to qualified electrical work.

Technical power and a common ground reference

Most hum and buzz in an AV system comes from how the equipment's grounds relate to each other through the power system. The most effective prevention is decided at the power plan, not in the audio rack.

Technical power is a supply dedicated to the audio, video and control equipment and nothing else: not lighting dimmers, not motors, not catering, not air conditioning. In permanent installations it may be a separate panel with its own grounding arrangement, sometimes an isolated ground receptacle, marked with an orange outlet or a triangle in North America, whose ground is run separately back to the panel. On shows it is usually a distro or a set of circuits reserved for the sound and video systems, fed from the same source.

Powering the connected signal equipment — the audio console, the stage racks, the amplifiers, the video system that shares audio with them — from the same technical power source gives all of it a common ground reference. Their grounds all return to one point, so there is no difference in potential between them for a ground loop to flow through. Powering the console from one side of a hall and the amplifiers from a distro on a different supply at the other side is how systems acquire a hum no one can find.

The electrician provides technical power. The technician asks for it in the power plan, keeps other departments' loads off it, and plugs every connected piece of signal equipment into it.

Dimmers, motors and electrical noise

Some loads put electrical noise back onto the power system. Traditional phase-control dimmers for incandescent lighting chop the mains waveform, creating sharp edges full of high-frequency noise and a characteristic buzz in audio that rises and falls with the lighting levels. Large motors, chain hoists, compressors, catering equipment and air conditioning create spikes and dips when they start and stop. Switch-mode power supplies in LED products add their own high-frequency noise.

Noise gets into signals two ways. Through the power, when audio equipment shares circuits or grounds with a noisy load. And through the air, when power cable carrying noisy current runs alongside signal cable and couples into it.

So noisy loads are kept on different circuits from technical power, ideally different distros, and power cable is kept apart from signal cable, crossing at right angles where they must meet. A buzz that follows the lighting levels points straight at dimmers; a thump when a hoist starts points at motors on shared power.

UPS types

An uninterruptible power supply, UPS, keeps equipment running from a battery when the supply fails. For a show, that might mean the media server, the switcher, the console or the network keeps running through a generator hiccup or a tripped circuit, long enough to switch to another supply or to finish a sequence cleanly. Different types protect against different things.

A standby, or offline, UPS passes mains straight through and switches to battery when the supply fails. The switch takes a few milliseconds, which most equipment rides through and some does not. It does little to clean the power while mains is present.

A line-interactive UPS adds regulation, correcting moderate voltage sags and swells without using the battery, and switches to battery on failure, also with a short transfer.

An online, or double-conversion, UPS runs the equipment from its inverter all the time, continuously converting mains to DC and back to clean AC. There is no transfer gap, and the output is isolated from most disturbances on the supply. It is the right choice for the most critical equipment and for generator power, and it is larger, hotter and more expensive.

Every UPS is rated in VA and watts, and its run time falls sharply as its load rises. Batteries age, so a UPS is tested by actually removing its supply during setup, and one whose battery warning is on is not relied on. And a UPS feeding amplifiers or large loads is usually a mistake: they empty the battery in moments and are rarely what needs protecting.

Power sequencing

Switching a system on and off in the right order protects loudspeakers from thumps and keeps inrush from tripping breakers. Sources and processing come on first, amplifiers and powered loudspeakers last; the order reverses when switching off.

A power sequencer does this automatically: a rack unit with outlets that switch on one after another, with a delay between them, from a single switch or a control system. It also spreads inrush current over several seconds. Where one is installed, equipment is plugged into the outlet position intended for it, because an amplifier plugged into the first outlet defeats the purpose.

Without a sequencer, the same order is followed by hand, rack by rack, and it is written on the power plan or a label on the rack so the next crew does it too.

AV wants clean, reliable power, not just enough: electrical noise causes hum/interference (keep power and signal apart), and dips/surges/interruptions disrupt or damage gear — so important systems use power conditioning and backup (UPS), applying reliability thinking to power. Applying electrical knowledge means knowing gear's needs, distributing without overloading, working safely, ensuring clean/reliable power, and staying within safe power use while calling an electrician for actual electrical work — the foundational competence (part of CTS knowledge) every AV pro needs.

UPS types compared

Keep apart

What stays off technical power, and what shares one clean source.

Off technical power

• Lighting dimmers.
• Chain hoists and motors.
• Catering, heating and air conditioning.
• Anything not connected to the signal system.

On one technical power source

• Audio console and stage racks.
• Amplifiers and powered loudspeakers.
• Video equipment that shares audio with the sound system.
• Playback and recording.

On the job

A theatre-style awards show. The sound system has a low buzz that rises and falls as the lighting changes, loudest when the stage is dimly lit with warm tungsten fixtures.

You check the power plan. The front of house audio rack is on a circuit from a distro that also feeds the house's conventional dimmer rack, because that distro was the closest to the mix position. Everything else in the audio system is on the technical power distro at the side of the stage.

Two faults in one. The dimmers are putting noise onto the circuit feeding the audio rack, and the audio rack's ground reference is a different distro from the stage racks and amplifiers it is connected to.

At the dinner break, with the electrician's agreement, you run a dedicated power cable from the technical distro to front of house along the edge of the room, apart from the lighting cable, and move the audio rack onto it, switching off amplifiers first. When the show resumes the buzz has gone, and it does not return when the lights dim.

How to do it

1. Ask for technical power in the power plan.
2. Keep dimmers, motors, catering and other departments off it.
3. Plug every connected piece of audio and video equipment into the same technical source.
4. Run power cable apart from signal cable, crossing at right angles.
5. Put critical playback, switching and network equipment on a suitable UPS, and test it by removing its supply.
6. Follow the power sequence, amplifiers last on and first off.

What goes wrong

Practice it

Answer before checking.

Pathways to Licensure

This book teaches you to use power safely as an AV tech. If you want to go further and do electrical work legally, here is the road to becoming a licensed electrician.

Where AV power knowledge ends and the trade begins

Everything in this book prepares you to use power safely as an AV technician: reading a label, calculating load, distributing power, recognising hazards, and knowing when to stop. It does not make you an electrician, and it was never meant to.

Installing or altering building wiring, working inside electrical panels, running permanent circuits, and almost anything beyond plugging into existing, properly installed outlets is electrical work. In nearly every jurisdiction that work is legally restricted to licensed electricians.

If you discover you enjoy the power side of AV and want to do that work for real — legally, and for considerably better pay — the route is to become a licensed electrician. This chapter is a map of that route. Treat it as guidance, not legal advice: the exact rules vary by state and city, so always confirm with your local licensing board.

The licensing ladder: apprentice, journeyman, master

There is no national electrician's licence in the United States. Licensing is granted by individual states, and sometimes by individual cities, so the precise hours, exams, and titles differ from place to place. The ladder itself, however, is remarkably consistent everywhere.

You begin as an apprentice. An apprenticeship typically runs four to five years and combines paid on-the-job training with classroom instruction. The common benchmark is roughly 8,000 hours of supervised on-the-job training plus several hundred classroom hours — often in the range of 144 to 180 hours a year. Apprentices earn while they learn, usually starting near 40 per cent of a journeyman's wage and stepping up about every six months.

After the apprenticeship you sit a state or local exam to become a journeyman electrician — licensed to do electrical work, pull permits, and work without direct supervision. The next step, master electrician, generally requires another year or two of journeyman experience and a further exam; masters can design systems, supervise crews, and, depending on the state, hold the contractor licence needed to run a business.

Getting in: union, non-union, and the entry requirements

Most apprenticeships are entered one of two ways. The union route runs through the Electrical Training Alliance — the joint programme of the International Brotherhood of Electrical Workers (IBEW) and the National Electrical Contractors Association (NECA) — delivered locally through Joint Apprenticeship and Training Committees, or JATCs. Union programmes are competitive to enter and known for strong pay, benefits, and pensions.

The non-union route runs through merit-shop programmes such as those of the Independent Electrical Contractors (IEC) or Associated Builders and Contractors (ABC), or through an individual contractor who sponsors you. Both routes lead to the same journeyman exam and licence.

Entry requirements are modest and attainable: you generally need to be at least 18, hold a high school diploma or GED, often have a year of high-school algebra, carry a valid driver's licence, and pass a basic aptitude test and a drug screen. Some people first complete a pre-apprenticeship or a community-college electrical programme to strengthen an application, but that is optional. Importantly, the apprenticeship is a paid job, not tuition you owe — you are hired and paid from day one, which makes this one of the few skilled careers you can enter debt-free.

The exam, the Code, and finding your state's rules

The licensing exam is built around the National Electrical Code, NFPA 70, usually combined with state and local amendments and some business-and-law content. The Code is revised on a three-year cycle; the 2026 edition was issued in 2025, but each state adopts new editions on its own schedule, so in early 2026 many states still test on the 2023 or even the 2020 Code.

This matters in one very practical way: study the exact Code edition your state has currently adopted, not simply the newest one, because the exam is written to the adopted edition. Your state licensing board publishes which edition is in force.

To find your own requirements, look up your state's electrical licensing board or department of labor. That page lists the required hours, the approved apprenticeship programmes, the exam provider, the fees, and any additional city licence you may need. Because the details genuinely vary, treat this chapter as the map and your state board as the authority — when the two disagree, the board wins.

Is this path for you? Mapping AV onto the trade

Your AV background is an advantage on this path, not a detour. You already read labels, think in volts, amps, and watts, calculate load, respect grounding and safety, and work cleanly under a deadline — exactly the habits an apprenticeship sets out to build.

Some of what you have learned overlaps directly with an electrician's world: power distribution, circuits and breakers, load calculation, and the discipline of working to code. You will start a step ahead of someone with no trade exposure at all.

Be clear-eyed about the trade-offs. Becoming licensed takes years of committed, full-time work and study, and apprentice pay starts low before climbing steeply. In return you gain a portable, licensed, well-paid career with strong demand — and even if you stay in AV, the knowledge makes you far more valuable on any crew. Whether you go all the way to a licence or simply deepen your power knowledge, the next concrete step is the same: contact a local IBEW/NECA JATC or a merit-shop programme, and look up your state board's requirements.

Practical sign-off

Electrical competence is reinforced safely on the job. The learner calculates load, distributes gear across circuits without overloading, works safely around power, and correctly defers actual electrical work to a qualified electrician. A mentor signs off when the learner uses power safely and within their limits. Note: this book builds awareness; it does not authorise electrical work.

• Explained volts, amps, and watts and calculated a device's draw
• Calculated circuit load and distributed gear without overloading
• Applied core electrical safety practices and respected grounding
• Correctly identified electrical work to defer to a qualified electrician

Entertainment electrician certification

A licence lets an electrician do electrical work. In the entertainment industry there is also a certification that recognises the specific knowledge of show power, and it is worth knowing about whether or not you pursue a full licence.

In North America, the Entertainment Technician Certification Program, ETCP, run by ESTA, certifies entertainment electricians. The certification covers the knowledge of portable power distribution, load calculation, grounding, generators, connectors and safety that a production electrician uses every day. Like the rigging certifications from the same program, it is not an entry-level certificate: candidates qualify to sit the exam through documented experience, or a combination of experience and electrical licensing or education, and the published content outline is a good map of what an entertainment electrician is expected to know.

Many venues, unions and production companies value or require it for the people responsible for show power, and it sits naturally alongside a licence rather than replacing one. The certification does not itself authorise electrical work where the law requires a licence.

Canada and other countries

The route in the rest of this chapter is written for the United States. The ladder is similar in many countries, and the details differ.

In Canada, electricians are certified by each province and territory, through an apprenticeship combining paid on-the-job hours and technical training, followed by a certification exam. The Red Seal programme lets a qualified construction electrician add an interprovincial endorsement, recognised across the country, by passing the Red Seal exam. The electrical code is the Canadian Electrical Code, adopted with provincial amendments, and each province's apprenticeship authority publishes its requirements.

In the United Kingdom, electricians qualify through apprenticeships and recognised qualifications, and work in the entertainment industry is guided by its own code of practice for temporary power at events. In much of Latin America, electrical work is regulated nationally, often with a professional registration for electricians and technical regulations for installations, and the details vary by country.

Wherever you work, the same two steps apply: find the body that licenses or certifies electricians where you live, and read its requirements before assuming what applies.

Glossary

What the gear actually looks like

Every device named in this book, in one place. Recognition is the whole point of Chapter 4 — use this page to attach a picture to each name before you meet it on a dock at six in the morning.

Audio

Dynamic microphone

Condenser microphone

Wireless handheld

Radio rack

Mixing console

Stage box / snake

Power amplifier

Main loudspeaker

Subwoofer

Stage monitor wedge

In-ear monitors

DI box

Video

Camera

Video switcher

Scaler / processor

Projector

LED wall panel

Confidence monitor

Lighting & control

Conventional fixture

Moving-head fixture

Lighting console

Dimmer

Show controller

Media server

Networking & infrastructure

Network switch

Patch bay

Equipment rack

Power distribution

Cable tester

A properly coiled cable

Connectors, close up

XLR

TRS / TS ¼-inch

SDI on BNC

HDMI

Cat5e / Cat6 (RJ45)

Fiber optic

DMX (5-pin XLR)

AC power — not signal