electrical

Gabriel Rochette · September 18, 2009

Hi,

I'm looking for a real answer about real amps available when we shoot in location with a DRYER connector who split in two phases of 120v.

First, How many amps in a dryer connector ?

Also... How many amps available in each phase who receive plug box (U-groud) ?

Last interrogation ??? What is the amps difference between a DRYER plug and a STOVE plug.

Tanks a lot

Sorry for my fair english

Gabriel Rochette

Canada

Jim Hyslop · September 19, 2009

I'm looking for a real answer about real amps available when we shoot in location with a DRYER connector who split in two phases of 120v.

First, How many amps in a dryer connector ?

Also... How many amps available in each phase who receive plug box (U-groud) ?

Last interrogation ??? What is the amps difference between a DRYER plug and a STOVE plug.

Pick up a copy of the "Simplified Electrical Code" at your local Home Depot or Rona - it has a lot of information in it, and is a very useful reference. The Ontario version has a bright yellow colour (I think different provinces have different colours).

Dryers are typically 30 amps and stoves are typically 40 amps. I'm reasonably sure that's standard, and may even be the code requirement.

Each leg of the split phase will be able to supply the same amperage (30 for a dryer, 40 for a stove). U-Ground (aka Edison) plugs are rated at either 15 amps or 20 amps - depends if they have the horizontal tab on them. This is a 20 amp plug, and this is a 15 amp plug.

When plugging in everything, make sure you distribute the load evenly between both legs.

This is all in theory. In practice, you may not be able to draw the full capacity, especially if you use both a dryer and a stove receptacle. You have to account for all other loads in the home as well (does it have an electric water heater?) Any home more than 20 years old may only have a 60 amp service. Even older homes may have only 40 amps - stay away from them, as they will likely have knob-and-tube wiring.

Oh, and before you go in - make sure the house actually has an electric stove or electric dryer. If it uses gas, you won't have the power available to you.

--

Jim

Jim Hyslop · September 19, 2009

(I hit "Add Reply" when I meant to hit "Preview")

Since the u-ground plugs can only handle 15 amps, DO NOT connect them directly to the dryer or stove plug. You MUST protect them with a 15 amp breaker. The easiest way to do this is to get a small distribution panel, connect the supply cord to it, and put 15 amp breakers in it. If you are not 100%, absolutely certain you know how to hook this up, enlist help, preferably from a licensed electrician.

Back to the balanced load for a moment. The reason you want to balance the load is because the neutral line in the dryer/stove cable may be slightly smaller than the load lines. That's because in a well-balanced system, the neutral line (the white one) will carry little or no current. In a perfectly balanced system, you could (theoretically) remove the neutral altogether and the system would function normally. So, if one leg carries a lot of power and the other leg doesn't, then the neutral conductor could end up carrying a heavier load than what it was designed for.

If there is a likelihood of moisture, you may want to consider adding GFCI protection. Actually, that raises a question - do HMI lamps play well together with GFCI?

--

Jim

Gabriel Rochette · September 20, 2009

Thank you for your quick reply Jim,

Your answer help me a lot .

And i'm going to follow your guidance ... This book of Electrical code is a good idea !!!

Gabriel

Guy Holt · September 20, 2009

Hi, I'm looking for a real answer about real amps available when we shoot in location with a DRYER connector who split in two phases of 120v..... Gabriel Rochette Canada

Gabriel,

You have to be really careful when splitting 240 volt circuits as being discussed. If the 240 volt circuit is a four wire system (the receptacle has four slots: one for ground, one for neutral, and two for hot), one can use a distro box that splits the two hot circuits as long as it is wired so that each circuit has a ground and neutral.

Where you run into trouble is when the 240V circuit uses a three wire system (the receptacle has three slots: one for ground, and two for hot, and no neutral.) Many older household and industrial 240V receptacles use a three wire system (no neutral) because they were wired for the sole purpose of powering single phase motors or heating elements that draw a perfectly balanced load and return no current. A perfectly balanced load doesn’t require a neutral because the single phase service legs are 180 degrees out of phase and cancel each other out – hence there is no return that would require a separate neutral (a later revision to the NEC required all 240V circuits to include a neutral.)

You run into trouble with this kind of circuit when you start to pull an unbalanced load on your distro. And, where under most production situations you can never perfectly balance your lighting load, the two 120V circuits that make up this 240V circuit will not have 100% phase cancellation and the extra current of the high leg will not have a safe return path because by necessity with a three wire system you have had to bond the ground and the neutral in the splitter box (after all what else can you do with the ground and neutral of your splitter box but to bond them when plugging into a three wire 240V circuit.) Not only is it unsafe, but bonding ground and neutral after the service side of a main service head is a violation of the National Electrical Code (NEC.) To quote Mike Holt, of Mike Holt Enterprises, Inc. (A Leading Electrician Training Program in FL): “The National Electrical Code requires a neutral-to-ground connection to be made at service equipment only and there shall not be any neutral-to-ground connection on the load side of service equipment [250-23(a), 250-24(a)(5)]” (full excerpt is available online at his website)

The only safe way to pull power from three wire 240V circuits is to run your lighting load through a 240v-to-120v step down transformer. A transformer converts the 240 volts supplied by these industrial and household 240V receptacles back to 120 volts in a single circuit that is the sum of the two legs of the circuit. For instance, a transformer can make a 60A/120v circuit out of a 30A/240v dryer circuit that is capable of powering bigger lights, like a 5k. What makes it safe to use a step town transformer with three wire 240V dryer/range/motor circuits is that the transformer automatically splits the load of whatever you plug into it evenly over the two legs of the 240V circuit. Where there is no high leg, the loads on each leg of the 240V circuit cancel out and there is no return that would require a separate neutral.

And unlike 240V splitter distro boxes where you have to meticulously balance your load, a transformer greatly simplifies your set electrics by automatically splitting the load. As long as you plug lights in through the transformer, you no longer have to carefully balance the load over the two 120V circuit/legs because the transformer does it for you automatically. If you outfit the transformer with a 60 Bates receptacle, you can use 60A GPC extension cables, 60-to-60 Splitters, and fused 60A GPC-to-Edison Breakouts (snack boxes) to run power around set - breaking out to 20A Edison outlets at convenient points (rather than one central point.) The best part about using a transformer with a 240V receptacle in this fashion is that no matter where in the distribution system you plug in, the transformer automatically balances the additional load, so that you don't have to.

I use transformers to power bigger HMIs (2.5-4Kw) in situations where a tie-in is not an option and the budget doesn’t permit for a tow generator. Where the production budget is particularly tight, I use a package consisting of two transformers and a portable generator. I use one transformer to access more power through a 240V circuit on location to run lights inside; while the other I use to bring larger HMIs in the windows from outside. This approach eliminates the need for a dangerous tie-in or expensive tow generators, it also greatly reduces the amount of cable that has to be run.

For those who would like to see samples of what can be accomplished with this basic package, I have attached these links to production stills of the PBS and History Channel historical documentaries shot entirely, or in part, with just a couple of transformers and a Honda generator.

The History Channel’s “Unsolved History” episode “Presidential Assassins”

American Experienes Typhoid Mary Biography "The Most Dangerous Women in America"

WGBH’s Ben Franklin Biography “Franklin”

Or, use this link for more details about using step-down transformers on set: . By giving you access to more house power through common 240V house outlets, a transformer can quite often eliminate the need for tie-ins or generators.

- Guy Holt, Gaffer, ScreenLight & Grip, www.screenlightandgrip.com