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Old September 13th, 2007, 03:13 PM   #1
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Hey folks, I'm a video production student at Ball State University. I'm in a beginning lighting class, so I apologize for any math/technical mistakes...

Okay,

I was shooting a lighting assignment earlier this week where we were required to find a location, set up some lights, and shoot something with "creative lighting."

We got access to an entire floor above a bar. However, we could only get our acress in the evening. So it was pitch black outside(ugh)

The space was unfinished and under renovation. The floor's electrical wiring had been torn apart. They are planning on redoing it, but at the time it was in disarray. The floor only had one 20A circuit.

We had two 1k lights and one 250w. This should pull just over 20amps (right?) I know this is bad, but we had to use them to get enough light. We left everything on for half an hour and the circuit didn't blow, so we thought we were in the clear.

Then, 50 minutes later, everything went out.

I know we were over the limit of the circuit, so it makes sense that it blew, but- it worked for the first thirty minutes.

We only went over basic electrical stuff (watts, amps etc.)

So-my question is this-Why didn't it blow right away?
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Old September 13th, 2007, 04:15 PM   #2
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I'm assuming it was breakers and not fuses? Although a fuse might take a bit longer than a breaker to open up. It's really hard to say. Could have been a lot of things. But, since everything was "torn apart" it could indicate they were going from fuses to breakers in the conversion perhaps.
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Old September 13th, 2007, 04:20 PM   #3
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Breaker not Fuse

"I'm assuming it was breakers and not fuses? Although a fuse might take a bit longer than a breaker to open up. It's really hard to say. Could have been a lot of things. But, since everything was "torn apart" it could indicate they were going from fuses to breakers in the conversion perhaps."

Yes, you are correct, it was a breaker...
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Old September 13th, 2007, 04:25 PM   #4
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Of course, in a commercial environment, you may more likely get away with the load you had (20a) because commercial circuits are usually 20a. In someone's home however, I would guess the breaker would have tripped right away as most home circuits will be 15a and not even an 2000w load would work on that.
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Old September 13th, 2007, 04:50 PM   #5
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Yeah, the second floor was 20 Amps, so we knew we could get at least 2K and be safe, but the 250 put us over by a little.

Is it normal to be able to have a larger load than 20A on a 20A circuit? In a pinch, how much leeway do you have?
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Old September 13th, 2007, 05:07 PM   #6
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It all depends.

Old breakers can trip at lower draw than a new breaker. Voltages from the power company vary. Surges can trip a breaker that's operating at near-capacity. Can you be sure there was nothing else on this circuit?

Most people will:
Know where the breakers are.
Not put more than 2000W (18a) on a supposed 20a circuit. 1650W (15a) if they think wiring is old or suspect.
Burn their lights for many hours test if shooting a live event that can't be replicated.
Carry long 12ga extensions (stingers).
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Old September 13th, 2007, 06:22 PM   #7
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Actually I think older breakers are far likelier to last longer past the trip point and that's one good reason many replace older breakers. Perhaps thats the best explanation why you got away with it for a while. But, don't do that too often though ;-). You're definitely putting a strain on wiring that you don't know much about and can't see within walls.
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Old September 14th, 2007, 05:53 AM   #8
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Thanks

Thanks for the speedy reply!
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Old September 14th, 2007, 07:30 AM   #9
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You might want to look into fluorescent or HMI lighting. Reflectors can sometimes substitute for one of your lights. Lots of places have insufficient electrical service and if a problem had happened and the investigators found 2,250 Watts of lights plugged into a 20A breaker in a burnt building, it could cause problems for everyone. Personally, I don't like to ride a circuit beyond about 80% for more than several seconds.

Breakers don't have built-in digital meters so it probably just took it a while to heat up before it got to the point it would trip. Also, as circuits heat up they increase in resistance which causes heat to then build up faster. It is a self-fulfilling cycle that gets to a breaking point suddenly.
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Old September 25th, 2007, 08:01 PM   #10
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Awesome! Thanks, HMI lighting would have been a good idea. As far as florescent lighting goes, I only have access to BIAX lights, which are a very large and soft source.

Do they make hard florescent lights?
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Old September 25th, 2007, 08:39 PM   #11
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No, no hard fluorescent lights yet. The source is just too big and not concentrated enough to make the point light source needed for a usable instrument. To get a bulb bright enough it would be huge and the corresponding mirror and lens to focus it would also be very huge. I just don't see a fluorescent hard light in the near future. HMI is the best energy efficient alternative as Marcus pointed out and LEDs in the future may also have promise once they can come down in cost and rise in wattage/output.
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Old September 27th, 2007, 04:24 PM   #12
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I'm glad we have 230V in Germany... normal ciruits are 16A only, but you can have up to 3680 Watts on one circuit. Not enough sometimes still... :)
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