Article submited by IQ forum member acrobg


So you’ve got everything ready to go, you’re shooting on location in someone’s house, and suddenly all your lights turn off. Everyone has a brief panic. Someone (the best boy electric ideally) runs downstairs to the panel box, turns the blown breaker back on, and 2 minutes later, the same thing happens.
What happened?

Someone overloaded the circuit with motion picture lights, craft services pieces (that innocent coffee maker probably pulls around 12 amps when brewing the coffee), sound equipment, camera batteries charging, hair had to use a dryer quickly in the room, etc.

It always happens at some point, but the important thing to know is how to deal with it and try to prevent it from happening.

First of all, let’s assume we’re shooting in the US, or any other country that is 120volt service. Let’s also assume for now that we’re using power that we find at our practical location, meaning standard edison house plugs. We’ll talk about generators later.

How to know how much power is available in the room in which you’re shooting.
On your tech scout to the location, two electricians (usually the gaffer and best boy) will map out the entire house. One of them will sit at the panel box turning breakers on and off, and the other will take a tester around the house as circuits are tested (can be purchased at home depot or the like). The bedroom, for example, may have three outlets on various walls, but there is only one 15 or 20 amp circuit available in the room. The two electricians will communicate via walkie-talkie, and all outlets in the house (including all in the kitchen, laundry room, etc.) get mapped out on a piece of paper. The kitchen often has 3 or 4 circuits, and one ay even be good for thirty amps. This process, in a 3bed/2bath house takes from 1-2 hours for a pair who’s experienced.
On the day, as lights and equipment gets plugged in, the electricians will know that three 1k lights can’t be plugged in in the bedroom, and that 1 or 2 of them must be powered from other sources, and the proper amount of AC extension cable (stingers) can be brought to set.

How to know how much power a light draws

Note: There is some math here. I’ll do my best to keep it as simple as possible.
Lights are rated in watts. We have lights such as 150watt, 300watt, 650, 1000(1k), 2k, 5k, 10k, 20k, etc. Household medium-mogul-base light bulbs (tungsten and CFL both) also follow this same formula. Amps equals watts divided by volts. In other words, A=W/V. Volts we know to be 120. Watts are whatever the light is designated as. Let’s say we have a 1000 watt mole baby. Amps = watts / volts, so amps = 1000 / 120. This comes out to 8.3 amps actual load. Since adding a bunch of 8.3s together is a pain, we round that off to 10 amps. We call that paper load. Lights are ALWAYS rigged by paper load. There are two reasons for this. First, it provides a cushion. If in a pinch you have a 2k plugged into a 20-amp circuit, you’ve maxed it out, but if you suddenly at the last second need a 100watt lightbulb plugged in, it will still work without blowing the breaker. Second, when lights are turned on, they spike at higher than their amperage rating. This is why lights usually burn out when they’re turned on, as opposed to when they’re already running.

So, the actual and paper loads for some common tungsten lights are as follows (HMIs are special):
Light (watts) Paper Load(amps) Actual Load(amps)
100w 1a 0.83a
300w 3a 2.5a
500w 5a 4.2a
650w 6.5a 5.4a
1,000w 10a 8.3a
2,000w 20a 16.7a
5,000w 50a 41.6a
10,000w 100a 83.3a
20,000w 200a* 166.6a*

*20k lights do not run on 120v power, but their amperage must be factored into a generator as though it does run off 120

Some useful tricks to get the most power possible
Look at the clothes dryer plug in the house. You know, the 240v plug in the laundry room. At your local hardware store, you should be able to get what’s called a range plug. It will have a bunch of 120volt edison power plugs on it (if you can only get twist-lock, there are adapters you can get at the same store). Plug this into the 240 plug, and whatever its rating was on the panel box (say it said 30 amps, and it’s obviously a 240 plug), it’s now worth double, so long as you split the items evenly, ie no more than 30 amps on either side.
Always err on the side of caution. If you are going to be running power into a room from another room with a stinger, run it from the closest additional circuit possible. Meaning, if the kitchen is on the other side of the house, but the bathroom is right next door, run power from the bathroom, not the kitchen.
Know if the breakers are 15 or 20 amps.
If shooting in an office or commercial building, know where the panel box is, or have a rep from the building there the entire time you’re in the building who knows where the box is / how to reset breakers.

Big lights and touching on cine generators
All lights bigger than a 2k will not plug into house power. They draw too much current, and they also don’t have a standard edison plug. To run these lights, you must have a generator or be on a motion picture stage. Home depot generators (rental or purchase) will not power a 5000-watt light. You have to get a cine generator. If you are going to run power off a generator, there are many more safety concerns. Consult with the local fire marshall regarding local laws with generators, as well as hire an experienced best boy and electrical department so that the equipment will be operated safely. I have taught generator safety classes in the past. Remember, it’s a 6000-lb trailer that’s full of about 150 gallons of diesel fuel. Also, they can be known to run as little as 60 amps, or as many as 2400 amps. It is important to know that 1 amp across your heart will kill you. So safety with the equipment is necessary. The cables used to run big lights and get power out of generators are massive. A single 50-foot strand of 4-ought cable (referred to as 4/ø) weighs about 50lbs. To make a 50-foot run of cable of 4/ø requires 5 strands, or 250lbs of cable. Other cables, such as 5-wire banded (2-gauge cable), weighs 75lbs for 50 feet; 100-amp bates weighs about 40lbs for 50 feet (3-strand, 4-gauge cable). You get the idea. Also, electrical boxes that exist for generators have to be rented. And the generator has to be towed. It will always have a military hitch, and should only be towed by people who know what they’re doing. Note: U-Haul does not make trucks with military hitches.

Anyway, I hope this has taught you a little bit about how to help avoid power issues on a location, by knowing how much power can be pulled through a house, how much power your lights draw, and then being able to avoid a problem when your’e on location and the lights suddenly go off from lack of planning.


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