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Author Topic: 2 575 Watt Fixtures on a 1200W Dimmer - Will they hold?  (Read 5152 times)

Tom Boisseau

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2 575 Watt Fixtures on a 1200W Dimmer - Will they hold?
« on: February 19, 2008, 05:13:25 pm »

What are your experiances with this?  I don't plan to do this on a regular basis, but if I try to run 2, 575 watt fixtures on a 1200W dimmer, will the circuit breakers on the pack hold?
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Phil LaDue

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Re: 2 575 Watt Fixtures on a 1200W Dimmer - Will they hold?
« Reply #1 on: February 19, 2008, 05:19:03 pm »

Mathematically you have 50 watts of capacity remaining.
The unit should be fused for 10 amps at 120 volts.
If for some stupid reason it is rated for less than 10 amps you could be in trouble.

Ron Hebbard

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Re: 2 575 Watt Fixtures on a 1200W Dimmer - Will they hold?
« Reply #2 on: February 19, 2008, 05:24:34 pm »

Tom Boisseau wrote on Tue, 19 February 2008 22:13

What are your experiances with this?  I don't plan to do this on a regular basis, but if I try to run 2, 575 watt fixtures on a 1200W dimmer, will the circuit breakers on the pack hold?


Hello Tom;

A few thoughts:
- In theory it works fine
- If I was living in bump-button land I'd be worried
- If I was in a theatre situation, I'd set 'patch at level' at 90% and sleep nights
- In any case, keep an eye on your dimmer pack's total dissipation; per line cord if you're using a small pack with two power input cables.

Toodleoo!
Ron Hebbard
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Tom Boisseau

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Re: 2 575 Watt Fixtures on a 1200W Dimmer - Will they hold?
« Reply #3 on: February 19, 2008, 05:40:51 pm »

I have a pretty good grasp of the theory and Ohm's law.  However in practice I have often found that a "standard" say 20amp circuit in a panel box will almost never hold a full 20 amps for any length of time.  

So I'm hoping someone can chime in here who has actually tried this and let me know their experiences.

Thanks,
Tom
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Mac Kerr

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Re: 2 575 Watt Fixtures on a 1200W Dimmer - Will they hold?
« Reply #4 on: February 19, 2008, 06:29:34 pm »

Tom Boisseau wrote on Tue, 19 February 2008 17:40

I have a pretty good grasp of the theory and Ohm's law.  However in practice I have often found that a "standard" say 20amp circuit in a panel box will almost never hold a full 20 amps for any length of time.  

So I'm hoping someone can chime in here who has actually tried this and let me know their experiences.

Thanks,
Tom
It depends a bit on how old the breaker is, and the variances in production. Circuit breakers don't trip due to current, they trip due to heat. As they have high current passed through them they heat up, and at some point trip. Most breakers will hold well over their rating for short periods, in audio we get a lot of benefit from that behavior because of the transitory nature of the current draw. With lighting, where the load is likely to be on for longer periods at a time you may keep heating the breaker to the point where it starts tripping at its rated current. The way to know for sure is to try it.

Mac
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Tony "T" Tissot

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Re: 2 575 Watt Fixtures on a 1200W Dimmer - Will they hold?
« Reply #5 on: February 19, 2008, 07:23:27 pm »

I used to have bad experience running 4 S4 575 on 2400 watt dimmers. To the point where we would either patch max to 70% or just go 3 per dimmer.

If you don't have enough dimmers (I never did), hopefully your board will let you put a max value on the channel. The brightness difference isn't "overly" apparent unless it's low transmissivity color.

These were older rack-mounted SCR - circa 70/80s. Can't remember brand name.
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len woelfel

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Re: 2 575 Watt Fixtures on a 1200W Dimmer - Will they hold?
« Reply #6 on: February 19, 2008, 11:46:43 pm »

Just because an outlet/dimmer is rated for X watts doesn't mean it's actually receiving it, dimmer or not.  

Edit:  Sorry, didn't see all the responses. I'll skip the lecture and say, yes, I've done it.  And gotten away with it.  I don't like doing it, and I always try and keep that dimmer/circuit below its capacity, but yes, it can be done.

Of course, that doesn't mean that it will work for you.  Just too many variables to consider.

jeffhtg (Jeff Kenney)

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Re: 2 575 Watt Fixtures on a 1200W Dimmer - Will they hold?
« Reply #7 on: February 20, 2008, 08:05:15 am »

Our engineer specs call for a 75% panel load  - this can get expensive on larger installations. But we NEVER have electrical problems when spec'ing.

Some dimmers are more robust than others - when approaching maximum rated load I set my cue masters / gm / channel limiters / etc at 90%. Check for single channel max load as well as total dimmer capacity. It sounds like you should be okay.

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Silas Pradetto

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Re: 2 575 Watt Fixtures on a 1200W Dimmer - Will they hold?
« Reply #8 on: February 29, 2008, 05:26:30 pm »

NEC specifies a circuit breaker cannot be loaded any more than 80% capacity. So no.
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Rob Timmerman

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Re: 2 575 Watt Fixtures on a 1200W Dimmer - Will they hold?
« Reply #9 on: March 01, 2008, 06:11:42 pm »

They also make an exception for theatrical lighting fixtures, allowing the breaker to be loaded to 100% of its capacity.

The exact details escape me though, and I don't have my copy of the Code handy to give a reference.
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