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Back to Basics: Electricity on Set

Electricity is vital to what we do. Unless you’re making a silent film outdoors at noon, you’re going to have to plug something in to get your masterpiece shot.

On big shoots, you’ve got an on-set crew for dealing with electrical – indie shoots, not so much. So here’s some VERY basic info that you should know. Again, this isn’t everything; hopefully it’s just enough to keep your set running and not on fire.

 

(Not) Short Circuits

An example of a circuit breaker panel. The orange indicates that these circuit breakers have been “tripped” – probably because someone didn’t read this article.

Every outlet you plug into is on a circuit. Each circuit in a house or business can handle a certain amount of electricity flowing through it. When that capacity is exceeded, the circuit breaker trips, and all power is cut off to that circuit.

You never want to trip a circuit. It delays shooting, indicates that you need to re-cable your gear, and generally is unprofessional. Avoiding a trip is pretty simple: add up the load you want to plug in, then make sure the circuit can handle the load.

Most circuits in America are either 15 or 20 amps. To be sure, check the breaker panel – it will say on the switches (or worse, on the fuses). If you can’t get to the breaker panel, I normally assume 15 for houses and 20 for businesses (unless the business is in an older un-renovated building).

Now, add up your loads. All your lights will have a wattage number, as will other gear – it’s printed on there, just look around. For the sake of argument, let’s say I’m lighting with a 1000w key, 650w fill, and 150w backlight – 1800W total.

But wait! We’re now comparing watts to amps!

Fear not – there’s math for this.

Watts/Volts = Amps

The volts value is dictated by what country you’re in. Here in America, the standard is 120V on paper and 115-125V in reality.

But that doesn’t matter – we’re going to use 100V. Not only does this make the math super-easy, it gives you some overhead for the inevitable spikes, equipment inefficiencies, and producers who plug whatever they want into whatever they want. And before you jerks complain, I’ve personally had a single 2000w light trip a 20A breaker due to a faulty switch. A bit of conservative estimation never hurt anyone.

Anyway, so back to our example. We’ve got 1800W running on 100V, which gets us 18 amps for the load. Now we know that we can safely run that load on a 20A circuit, but not on a 15A.

 

Cables and Power Strips

Most of the time, you won’t be plugging each and every light into a wall outlet. You’ll be using extension cords (called “stingers” in real production) and power strips (still called power strips). And they too have load limits.

Let’s talk stingers first. The load that can be carried by a stinger is dictated by the gauge of its wire; thicker wire can safely carry larger loads.

In America, wire gauges are listed as AWG – the lower the gauge, the thicker the wire. Real production stingers are usually 14AWG or thicker; regular consumer extension cords can be almost anything.

You could reference a table to determine which AWG you need for your load – but normally the cable will say right on it how much it’ll handle. And if you go to Home Depot, the displays even list the load limit on the front. Most common are 13A, 15A, and 20A.

Power strips are even easier – flip them over, and it’ll be listed on the back. Most are 15A, though I’ve seen some 13’s and even 10’s.

Why should you care? Because if you overload a stinger or strip, the copper inside gets too hot, melts through the insulation, and can start a fire.

 

This is what happens when you overload a powerstrip. Image: Austin Statesman

Don’t Take Things Apart

It’s pretty common for the curious among us to take things apart to see how they work. Usually it’s harmless – but it’s actually more dangerous than you’d think. Even unplugged, many electrical devices can retain enough current to kill you.

Inside most devices are things called capacitors. These little components store energy, charge almost instantly, and can take a while to discharge even after being unplugged. So even an unplugged device can have enough energy in it to kill you.

 

You Are Not An Electrician

Most important is knowing what you don’t know: namely, that you’re not an electrician. Follow the advice above and you should be able to safely plug things in – but please, don’t go beyond that. Just because you’ve seen a professional do something that looks simple doesn’t mean you should do it yourself.

As with anything, the key to safety is knowledge and caution. Keep that in mind and maybe your set won’t go up in flames.

 
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