Power on Location: Generators, Batteries, and Not Blowing a Circuit

You are three setups into a corporate shoot in a client's office. The talent is finally loose, the corner of the room looks right, and you flip on the second 2K to build out the background. The whole floor goes dark. A breaker in a closet you cannot find just tripped, and now you are the crew that knocked out power to a working office. IT is walking over. That is the fastest way to lose a room, and it is almost always avoidable.

Power is the least glamorous part of a lighting package and the one that ends days early. Camera and grip get all the attention, but the shoot lives or dies on whether the electrons show up reliably for ten hours. The good news is that the math is simple, the decision tree is short, and once you have run the numbers a few times you stop guessing. This is the working version of that math.

The only formula you need

Watts equal volts times amps. That is the whole thing. In the United States a standard wall outlet is nominally 120 volts, so amps equal watts divided by 120. A 1,000 watt tungsten fixture draws about 8.3 amps. A 2,000 watt draws about 16.7. Commit that one division to memory and you can size any load in your head on set.

The number you care about is not the fixture wattage, it is the circuit rating. Household and small-commercial circuits come in two flavors: 15 amp and 20 amp. A 15 amp breaker at 120 volts can theoretically carry 1,800 watts. A 20 amp breaker can carry 2,400. But you never load a circuit to its rating, because film lights run for hours and the National Electrical Code treats anything on for three hours or more as a continuous load, capped at 80 percent of the breaker rating.

That 80 percent rule is the single most useful thing in this post. It turns the theoretical numbers into working numbers:

• A 15 amp circuit is good for 12 amps continuous, or 1,440 watts.
• A 20 amp circuit is good for 16 amps continuous, or 1,920 watts.

So a single 2K tungsten fixture, at 16.7 amps, already exceeds the safe continuous load of a 20 amp circuit by itself. It will run for a while, then it will trip, usually at the worst possible time. Plan against the 80 percent number, not the breaker rating, and most of your power problems disappear before they start.

What your lights actually draw

Fixture draw has changed enormously in the last decade, and if your mental model was built on tungsten, it is now costing you circuits. Here is the practical picture across the three technologies.

Tungsten is the hungriest and the most predictable. Watts in equals watts of heat and light out, and the draw is exactly the lamp rating divided by 120. A 650 is 5.4 amps, a 1K is 8.3, a 2K is 16.7, a 5K is a staggering 41.7 amps that needs its own dedicated feed. Tungsten is honest but expensive to power.

HMI is far more efficient per watt of output, but it lies to you about draw. The ballast pulls more than the lamp rating, and older magnetic ballasts without power factor correction pull a startup surge well above the running number. A 1.2K HMI has a 1,200 watt lamp but pulls closer to 1,600 watts at the wall once you count the ballast, roughly 13 amps running and more on strike. Read the ballast plate, not the lamp, and give HMIs headroom for the inrush.

LED is what actually rewrote location power. A modern 1,200 watt LED point source draws about 12 amps and throws light in the neighborhood of a much larger tungsten unit. A 600 class LED draws about 6 amps. A tabletop panel draws under 2. You can run a full three-point interview package off a single 20 amp circuit with LED where the same look in tungsten would have needed a tie-in or a generator. If you are still sizing power like it is 2012, you are hauling copper you no longer need.

The interactive companion on this post lets you stack real fixtures and watch the total amperage and required circuit count move in real time, so you can feel where a package tips from wall power into generator territory.

When a wall circuit is enough, and when it absolutely is not

Wall power is free, quiet, and already there. For a lean LED interview package, one or two known circuits are genuinely all you need, and dragging a generator to that job is overkill. The problem is almost never the total wattage. The problem is that you do not control the building.

A wall outlet does not tell you what circuit it is on. That duplex on the east wall might share a breaker with the outlet on the north wall, the break-room refrigerator, and a space heater somebody plugged in this morning. You budget 1,920 watts for your key, someone's coffee maker cycles on, and the combined load trips a breaker you were never told about. In an unfamiliar building you are loading a circuit whose other tenants you cannot see.

A few habits keep wall power honest:

• Map the circuits before you load them. Plug a work light into an outlet and start flipping breakers, or use a plug-in circuit tracer, so you know which receptacles share a breaker. Ten minutes here saves a blown take later.
• Spread the load across separate circuits on purpose. Two 20 amp circuits on different breakers give you 3,840 watts of clean headroom. Running everything into one convenient wall is how you find the breaker.
• Find the panel and get permission before you touch anything. Know where it is, know whether you are allowed to reset a tripped breaker yourself, and get the building contact's number before the crew arrives, not after the lights go out.
• Leave margin. Load a circuit to 80 percent of its rating and stop. The last 20 percent is not yours; it belongs to whatever else the building decides to turn on.

The honest ceiling on wall power is not a wattage figure, it is a trust figure. Two or three circuits you have personally traced and confirmed are dependable. Six mystery outlets in a building you walked into that morning are not, no matter what they add up to on paper.

The tie-in and the generator

When the package outgrows the wall, you have two ways up, and one of them is not a do-it-yourself job.

A tie-in is a licensed electrician connecting your distribution directly to the building's electrical panel or a dedicated disconnect, giving you access to real amperage. This is common on stages and larger commercial locations, and it is genuinely a lot of available power. It is also the line where you stop and hire a licensed electrician or a set electrician who is qualified and insured for it. Tapping a live panel is not a place to improvise, it is a place to get someone hurt or start a fire. If the job needs a tie-in, it needs the right person holding the wrench.

A generator is the more common answer on location, and it comes in two broad sizes. A portable inverter generator, the Honda EU7000is class, puts out roughly 7,000 watts peak and about 5,500 watts continuous, runs clean enough for sensitive gear, and is quiet enough to shoot near. That covers a mid-size LED package with room to spare. Above that you move to a tow plant: a trailer-mounted diesel generator in the 40 to 100 kilowatt range, a Multiquip Whisperwatt or similar, which is the workhorse of any commercial shoot running HMIs, big tungsten, or a full grip-and-electric package. A tow plant usually comes with an operator, and on a union job that is a specific role.

Two things to size for. First, headroom: never load a generator to its continuous rating. Give it 25 percent of margin the same way you give a wall circuit its 20, so the generator is not straining and your voltage stays stable. Second, and this matters in Texas: generators derate in heat. A machine rated for a cool day in a catalog puts out less on a 105 degree DFW afternoon in July, and the cooling and fuel burn both work harder. Size up for the summer, not for the spec sheet, and keep the fuel plan realistic for a long day.

Batteries deserve a mention because they have quietly changed run-and-gun work. A block battery or a large V-mount power station can run an LED fixture or two for hours, silently, with no fuel and no exhaust, which is exactly what you want for a quiet interview, a moving vehicle, or a location where a generator is a nonstarter. Batteries are not going to power a 4K HMI, but for small LED work they have replaced the putt-putt generator on a lot of jobs. Know their limits and they are the cleanest power on the truck.

Distro is just organized distribution

Distro is the unglamorous middle: the gear that gets power from the source to the fixture without melting anything or dropping voltage over a long run. Get it right and nobody notices. Get it wrong and you get flickering lights, tripped breakers, and hot cable.

The building blocks, from the wall out:

• Stingers are your extension cords, and the gauge matters. A 12 gauge stinger carries a 20 amp load. A long run on undersized cable drops voltage and heats up, so keep the runs short and the gauge heavy.
• Quad boxes and gang boxes turn one feed into multiple outlets so you are not daisy-chaining stingers into a fire hazard.
• Distro boxes and spider boxes take a larger feed and break it into individual protected circuits, each on its own breaker, so a single overloaded fixture trips one circuit instead of the whole system.
• Bates connectors and cam-lok are the higher-amperage connectors you graduate to past the standard household plug. Bates stage-pin connectors come in 20, 60, and 100 amp versions; cam-lok is what carries the big feeder cable from a generator or tie-in into the distro. This is where the electric department earns its keep.

Two safety points that are not optional. GFCI protection is required anywhere there is a wet or exterior location, and rain, pools, and morning dew all qualify. And a generator has to be properly grounded; a floating ground is a shock hazard, not a shortcut. If your package has reached the point where you are running cam-lok and a distro box, you have also reached the point where a qualified best boy electric or genny operator should be the one building it. That is not a luxury line item, it is the person who keeps the day safe and running.

The takeaway

Power planning is not complicated, it is just done in advance or done in a panic. Do the division before the truck is loaded: add up the draw of every fixture, compare it against the 80 percent limit of the circuits or the generator you actually have, and build in margin for the Texas heat and the mystery load on the building's breaker. A package that is planned to its real amperage runs quietly all day and nobody ever thinks about the power. A package that was eyeballed trips a breaker in front of the client, and that is the one they remember.

Run the numbers first. The breaker does not care how important the shot is, so make sure it never has to.