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Old February 18th, 2007, 07:51 PM   #1
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Volatge/electricity safety question

I've got access to about, oh, I'd say about a 5K kit right now.

There have been times, especially when lighting large spaces, when I've been tempted to blast 4 500w Tota's into some grid cloth hung between C-stands for a nice even fill, while simultaneously using 3 Arri 650's for key.

That would be about 4K of electricity. I'm no electrician, but I would think some issues might arise just sucking this out of the wall. What's the average household capacity for electricity? I'm on location all of the time. No soundstages, no generator trucks.

Is there a way to find out/calculate capacities for various buildings? I don't want to blow any fuses or bulbs, and I certainly don't want to start any fires. Is pulling 4K out of four socket fixtures in the same room the same as distributing the load out over seven sockets from different rooms?(I don't think it would be)

Where should I draw the line?

Thanks-
-Alex
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Old February 18th, 2007, 08:01 PM   #2
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The simple formula you need to know is wattage/voltage = current used. As an example using nice even numbers, you plug a 1200 watt hair dryer into a 120 volt outlet. Using the formula, 1200/120 =10, you'd be pulling 10 amps of current on what is usually a 15 amp capacity circuit. There are usually 3 or 4 outlets on one branch circuit so in this example, you only have 5 amps available to run anything else while the hair dryer is running before you trip a breaker.

Most household circuits are 15 amps. Kitchen areas are typically 20 amps because kitchen appliances tend to pull a lot of current.

You also need to make sure that you use a heavy duty extension cord on anything you plug in.

Keep your light stands weighted with bags so they don't fall over and keep flammables away from high wattage lamps for fire safety.

Be careful,

-gb-
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Old February 18th, 2007, 08:09 PM   #3
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It's not about how many rooms or how many sockets you are using. It's about how many separate circuits, and how much each circuit is rated at. It's dangerous to assume averages when pulling such a heavy wattage load in any given location. You should definitely check out the main panel at any location on a scout - ahead of the shoot, if possible. Find out which outlets are tied to which circuits, and don't overload them.

If you're working in a non-retrofitted space that is using fuses instead of circuits, the fire risk is way higher. Be especially careful.

You should take time to figure out which outlets are ganged together on a circuit - it may surprise you which ones are together, even in separate rooms. When people start assuming things about power, that's when things go wrong. Never guess - always know.
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Old February 18th, 2007, 08:16 PM   #4
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Quote:
Originally Posted by Alex Milne
Is there a way to find out/calculate capacities for various buildings?
Yes, just find the fuse panel and look at the capacity of the main breakers. But as others have said, it isn't really that simple. I think you will find older homes with 100 amp services and newer ones with 200 amps (especially if they have electric stoves and water heaters).

But the real problem will no doubt be one of not overloading individual circuits, as opposed to overloading the main breakers....
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Old February 18th, 2007, 08:19 PM   #5
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Quote:
Originally Posted by Greg Boston
The simple formula you need to know is wattage/voltage = current used.
To help remember this, think of: Watts / Voltage = Amps, or W/V=A. It's called the "West Virginia Law" (WVA) :-)
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Old February 18th, 2007, 08:32 PM   #6
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Quote:
Originally Posted by Boyd Ostroff
To help remember this, think of: Watts / Voltage = Amps, or W/V=A. It's called the "West Virginia Law" (WVA) :-)
That's the first I've seen that one. In college, we learned PIE. Power= I (current) X E (voltage).

If you arrange the three letters with the P on top and the I and E below, all separated by a line, it gives an indication as to how to solve for any one of the three values when the other two are known. Don't know if I can do it with HTML but I'll try.

P
___
I | E

So E is P divided by I, I is P divided by E, and P is I times E.

-gb-
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Old February 18th, 2007, 09:24 PM   #7
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Quote:
Originally Posted by Eric Darling
You should take time to figure out which outlets are ganged together on a circuit -
I don't mean to be whiny, but how would I go about doing this?

Thanks for the replies-
-Alex
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Old February 18th, 2007, 10:14 PM   #8
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The way I've done it is have one person at the switch box and one person with a mains powered lamp (or mains rated voltage tester). Prefereably with walkietalkies for easy comms.

Switch off all circuits, plug in lamp, then switch on powerpoint circuit #1 - does the lamp light? if not turn off circuit #1, switch on circuit #2, etc, etc.
When you work out what circuit the outlet is connected to, mark it - if possible with a permanent marker.
Repeat for all outlets.
Note: this requires the ability to turn off all the power, which some people won't like...

Once you know what is on each circuit, you need to take into account all loads on that circuit - eg you don't want to be half way through a scene and then the fridge clicks on and takes out the fuse/circuitbreaker...

HTH,
Kyle
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Old February 18th, 2007, 11:18 PM   #9
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Just for reference, Electrical code in the US mandates that all commercial buildings be fitted with 20 amp circuits. Most houses have 15. 20 amp circuits in areas of houses can be common, but not always the case.

As to checking them, you can go to Home Depot or Lowes and pick up a circuit tester pretty cheap. It comes in two parts. One part you plug into the circuit you intend to test - it sends out a frequency that is detected by the second part. You go to the breaker panel and scan the breakers and usually there is a lighted or audible indicator as to which circuit it is. Flipping breakers on and off works, but I doubt most people will be happy with that.

20 amps actually = 2400 watts at full load. You should always use only 80% to be on the safe side. If you have 4k worth of lights, 2 seperate circuits will be fine. Also, make sure you use a heavy duty SO or SOOW cord - probably 12ga if you intend to carry 20 amps. Don't use the orange extension cords, as most are only 16 or 14 gauge and will not properly carry your load. Overpowering cables is a great way to heat them up and start a fire.
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Old February 18th, 2007, 11:25 PM   #10
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Quote:
Originally Posted by Kyle Ringin
The way I've done it is have one person at the switch box and one person with a mains powered lamp (or mains rated voltage tester). Prefereably with walkietalkies for easy comms.
You can do it all by yourself without any walkie-talkies using this old electrician's trick. Plug a radio into the outlet you want to test. Turn the volume up high enough so you can hear it from the circuit breaker panel in the basement (or wherever). Now start flipping circuit breakers. When you hear the radio go off you'll know that you've found the correct breaker.

Before you start flipping breakers it's a good idea to know what kind of equipment might be connected to them. For example, it could be a bad thing to shut off someone's computer or telephone while they are using it!
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Old February 18th, 2007, 11:32 PM   #11
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If you want to be especially scientific, a circuit finder can come in handy in your ditty bag:

http://www.hgtv.com/hgtv/rm_safety_e...393502,00.html
http://www.zircon.com/SellPages/Scan...-Pro-Main.html
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Old February 19th, 2007, 04:20 AM   #12
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Quote:
Originally Posted by Boyd Ostroff
You can do it all by yourself without any walkie-talkies using this old electrician's trick. Plug a radio into the outlet you want to test. Turn the volume up high enough so you can hear it from the circuit breaker panel in the basement (or wherever). Now start flipping circuit breakers. When you hear the radio go off you'll know that you've found the correct breaker.
That's a good idea if the distances aren't great, but can involve lots of walking with one person though...
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Old February 19th, 2007, 12:56 PM   #13
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For residential shoots, bear in mind that in your part of the country, houses can be very old. Sometimes the wiring has been updated... and sometimes it's old knob and tube stuff, no ground, etc.

I drive a converted coach/bus and have become very adept at pulling power for my bus from various makes of panels and subpanels... and bypassing any branch circuits for power to insure that we stay safe of missing grounds, polarity problems, breaker trips, etc.

A gaffer's needs are little different... you too want uninterrupted, safe power. I would avoid any branch circuits and plugs that might not be up to the task and tap right off of the main or subpanel with a 30a 220v breaker (for well over 6kW of power), breaking the hot legs into 2 10ga stingers to pull wherever you need it. A couple hundred $ from Lowes or HD will give you everything you need... breakers, cords, boxes (use 20a receptacles), connectors, etc.

One blown circuit/fuse in the middle of your shoot will make it ALL worth it.

If you happen to luck into a 220v electric dryer plug on site, you can make up a connection without tapping into the panel at all.

If you're not comfortable working with AC, an electrician on-call can do these tasks in short order... and help you make up the kit you need.

HTH,
Brian Brown
http://www.brownland.org/blog/
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Old February 19th, 2007, 07:12 PM   #14
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Tie-ins have been illegal in Oregon for several years now unless you are or employ a licensed electrician.

Plugging into a 220v dryer or stove plug with a distro is a little bit more grey, but highly discouraged in these parts. Lighting & grip companies stopped renting such because of liability issues. They'd rather rent you a generator.

I suppose I agree on the issue of tie-ins. Pretty easy to get dead or burn down a house. You really have to know what you're doing.

I think it's irresponsible to suggest tie-ins in a public forum. Bear in mind that the original poster was asking beginner's questions about wattage and circuit capacities.
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Old February 19th, 2007, 08:17 PM   #15
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Seth, I think it's far more dangerous (and irresponsible) to pull multi-kW through wires and circuits of unknown age/ origin than to properly tap a new feed with appropriate-sized conductors and safety breakers.

But let me publicly re-state: If one needs an electrician to perform a tie-in due to inexperience and/or local/ regional codes, then get an electrician on site. In most cases, it's a ten minute job... and far more safer (and responsible) than using any existing circuit.
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