Adding up the watts

Working with electricity isn’t all that hard. It’s just that if you get it wrong things tend to melt, catch fire and blow up. So it pays to have basic knowledge of electrical before you put your life–and your crew’s lives–on the line.

The easiest and most valuable lesson you can learn is to calculate how many amps of power your equipment will need to draw. It’s actually very simple. Just divide the total number of watts by the power supply. So if you have a 2K light (short for a 2,000 watt light) and a 1K light  (1,000 watts) and you plan on connecting them to the power source, you just take the total watts–3,000–and divide by the power coming from the outlet. In the U.S. that’s somewhere between 110 and 120, so we’ll be safe and assume the lowest supply of 110. 3,000 divided by 110 gives us a little over 27 watts.

Since standard wiring has a limit of 20 amps (for many outlets it’s actually only 15), the 2K and the 1K together are going to trip a breaker on a standard power outlet. And if they don’t trip the breaker, you’re going to wish they had when the wiring in the walls starts to melt.

Now, you can go a lot deeper into on-set electrical: balancing the load and working with professional stage power receptacles. But this basic trick of calculating your amp requirements will help keep the lights on and the camera rolling.

Oh, and before you go plugging things into an outlet in a new location, use a Receptacle Tester to make sure the wiring’s set up right. You’ll be surprised how often electrical wiring is out of whack. Don’t believe us? You obviously weren’t there the day our $3,000 projector became a smoke machine.