Infographic: How to Avoid Tripping a Breaker with Too Many Lights

Working with high-powered lights on standard 15-amp circuits can be tricky business. Luckily, our peeps at Story & Heart are here to help.

In this handy-dandy infographic (and the accompanying blog post), the S&H team breaks down the simple calculation that will help you figure out whether or not plugging in that extra 300 watt lamp will trip the breaker, thus costing your production time that could have been better spent, you know, actually shooting things. Check out the infographic below.

Story & Heart Infofraphic- Avoid Tripping Breakers

Essentially, the formula comes down to this: take the number of amps (information that should be clearly displayed inside your breaker box), multiply it out by 120 volts (assuming you're in the US), and the resulting number gives you the maximum wattage that particular circuit can handle. Exceed that number with too many lights, and you're guaranteed to trip the breaker. For example, standard 15-amp circuits can support 1800 watts (15 x 120), which means that you can safely toss a 1K and a 600-watt lamp on that circuit with no issues. Two 1Ks, on the other hand, will almost certainly trip the breaker.

If you want more in-depth explanation of how to judge the capacity of household circuits, head on over to the Story & Heart blog. What are your best tips and tricks for managing electricity on household circuits? Share them down in the comments!     

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14 Comments

It should be noted that quite a few breakers (especially in newer and/or commercial facilities) are 20amps.

And that HMI's spike when they start. A breaker may be able to handle the load if you let HMI get going first, then add the rest of the load. Look up the lights you've got.

July 12, 2015 at 3:26PM

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Brooks Reynolds
Director/DOP
606

Great tips Brooks—thanks for adding them to the mix!

July 12, 2015 at 8:26PM

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Justin DeMers
Story & Heart Co-Founder
161

HMI spike is only true of lights with a magnetic ballast. HMIs with electronic ballasts actually ramp up to their true voltage (which may be higher than you would think).

In the link below there is a plate from a 1200w HMI ballast. The Pmax is what you have to worry about as that is volt-amps apparent load, which is a function of the load plus the power factor (without getting to in depth, power factor tells us how much extra power is required to run a light.). The Pmax is 2290 meaning at 120V, 2290/120=19Amps. You're not going to get anything else on that 20A circut, and can't run it on a 15A circuit. If you run stingers to it, your voltage may drop as well, which could make it not even run on a 20A circuit.

If your ballast is electronic power factor corrected (it won't always be, check when you're renting), most likely the Pmax will be lower.

http://www.screenlightandgrip.com/images/generators/ArriEBL1200_Ballast_...

July 17, 2015 at 12:51PM, Edited July 17, 1:35PM

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Arthur Love
728 Electrician
81

I will make it a lot easier. This is not exact math, but it includes a small, built-in margin of error: 100 watts = 1 amp. Stay under that and you should be fine. In other words, three 650 watt lights will work on a 20 amp circuit. Two 1,000 watt lights will just barely work on a 20 amp circuit.

July 12, 2015 at 4:11PM

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I was just about to make that comment. That system is called paper amps and it's a lot faster and easier. Most breakers are 20 amps but you should always scout the breaker box on a tech scout so you don't put DIT on the same breaker as a 2k.

July 12, 2015 at 4:16PM

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Danny Valentine
Gaffer/Director
220

Very cool tip Ken and Danny. Thanks for sharing!

July 12, 2015 at 8:27PM

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Justin DeMers
Story & Heart Co-Founder
161

For the new folks out there - don't forget that a different plug =/= different circuit. Especially if you are in a residence. Sometimes the circuits run really, really weird. I had an apartment once that had the entry hall, half of one bathroom, half of one bedroom, one socket in the kitchen and one in the living room all on one circuit. I'm assuming the contractor was drunk when they designed that one...

Also, 30 amp circuits do exist in many office/industrial settings (and some homes) they typically (!) look like this: http://i.stack.imgur.com/Bymwl.jpg but always check the actual breaker to be sure.

July 13, 2015 at 7:31AM

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Michael Carney
Director of Photography, Commercial Video, Stills
258

Not necessarily drunk. You often need separate circuits for heavy loads. In the living room, that might be a window air conditioner. In a kitchen, a stove; in bathroom, the heater, etc. The circuit that handles sockets in the foyer, half the bedroom, half the bathroom and one socket in living room and kitchen is likely meant to be used for lights and TV. The others are on separate circuits for heavier loads.

It is so much easier to plan for lights hookup in EU, since you get 220V, doubling the power in Watts for same current in Amps. 20A breaker will support 4,400W of lights.

July 17, 2015 at 9:44AM, Edited July 17, 9:44AM

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very informative info-graph.

July 13, 2015 at 9:10AM

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Anas Mubaideen
Director
96

A lot of houses and offices have unknown circuit maps, and you may not want to turn the breakers on and off to map it out because you may shut off a computer or a server or something like that. Go to Home Depot and buy a circuit sniffer. You plug in one end to an outlet and you have a wand that you hover over the circuit breaker. It will beep when it's over the breaker that corresponds to that outlet. I use that all the time when I'm using house power on location.

July 13, 2015 at 12:57PM, Edited July 13, 12:59PM

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Danny Valentine
Gaffer/Director
220

I was taught Watts = Volts x Amps or W=VA and i remember it by thinking West Virginia.

July 13, 2015 at 2:10PM, Edited July 13, 2:10PM

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I am so glad we got 230 Volts here in Germany and usually the household fuses are 16A. That means 3600W is possible on every circuit, much more headroom than in 110V areas of the world.
However, for my daily docu/tv work I hardly ever need power sockets anymore since I got two battery powered Tecpro Felloni Dedocolor LED panels plus a few smaller battery LED lights. You don't know how fun it is to be lighting with only lightweight, battery powered lights until you have tried it! :D

July 21, 2015 at 6:53AM

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Here's an easy way to remember the formula for calculating a circuit's wattage capacity. It's called the West Virgina Law, and uses that state's abbreviation: WVA.

So W = VxA. (watts = volts x amps)

July 30, 2015 at 8:24PM

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W Smith
Doer
241

Very helpful infographic!

July 29, 2016 at 10:27AM, Edited July 29, 10:27AM

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