Loading breakers

[mstaylor]

I am in a discussion about breakers on stage lighting equipment. I believe there is an exception where you can load breakers to 100% if rated to do so by the manufacturer. I do not have a copy of the NEC available so I can't look it up. Could someone quote the exception, if real, or let me that I am wrong. Thank you to Mike and others here that provide a excellent service.

 

[jumper]

Welcome to the forum.

210.19(A) and 210.20(A) have exceptions for loading circuits at 100%. Here is a link to on-line 2008 NEC.

http://forums.mikeholt.com/showpost.php?p=987226&postcount=9

Here is a good article on breakers

http://www.iaei.org/magazine/?p=3400

PS. I lived in Salisbury, MD for 5 years.

 

[nakulak]

you can read the NEC here (you just have to register)
http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=70

 

[iwire]

I am in a discussion about breakers on stage lighting equipment. I believe there is an exception where you can load breakers to 100% if rated to do so by the manufacturer. I do not have a copy of the NEC available so I can't look it up. Could someone quote the exception, if real, or let me that I am wrong. Thank you to Mike and others here that provide a excellent service.

That is not entirely accurate, all breakers and fuses for use with NEC applications can be loaded to 100% non-continuously. That is maximum load for no more than 3 hours at a time. If you did have 100% rated and marked breakers they could run at 100% forever.

See Article 100 for the definition of continuous load.

This is from the United Laboratories General Directory

Unless otherwise marked, circuit breakers should not be loaded to exceed 80 percent of their current rating, where in normal operation the load will continue for three hours or more.

Depending on you're application I find it doubtful that a particular theater circuit would be loaded greater than 80% for longer then 3 hours. If the circuit load drops below 80% at any time the '3 hr clock' restarts.

 

[dbuckley]

Is this a breaker in a dimmer as it came from the factory, as opposed to a breaker in a panelboard? If its built into the dimmer then (as I understand it) that in-equipment breaker is outside the perview of the NEC.

 

[iwire]

Is this a breaker in a dimmer as it came from the factory, as opposed to a breaker in a panelboard? If its built into the dimmer then (as I understand it) that in-equipment breaker is outside the perview of the NEC.

In that case the NECs only part in it would be the requirement to use the equipment at it is listed and labeled.

If I have a dimmer bank with 2000 watt dimmers is it typically OK to load them 100%?

 

[mstaylor]

In that case the NECs only part in it would be the requirement to use the equipment at it is listed and labeled.

If I have a dimmer bank with 2000 watt dimmers is it typically OK to load them 100%?

My understanding for the exception in a dimmer rack is it is fan cooled so it can run 100% for the three hour requirement. I agree that the breakers that you are tieing the dimmers to need to meet the 80% mark. I have a copy of a NEC at work but couldn't get to it. However I will mark the online version. Thanks for the help.

 

[zbang]

If I have a dimmer bank with 2000 watt dimmers is it typically OK to load them 100%?

Probably. The dimmers I've used were certainly constructed to 100% load (and, say, 35a scrs on a 20a rated dimmer). OTOH, after a couple of hours continuous at full load, it'll be a bit warm. Really depends on the output breakers. (I've put 2500w on a 2400w dimmer with the knowledge that it's not going to be used a full brightness for any length of time.)

And echoing previous posters, most dimmer packs count as manufactured assemblies, so NEC doesn't apply to the insides.

 

[wawireguy]

What happens if the breaker trips? Does it interupt a show that people paid to see? I'd err on the side of caution for something that has to do with a stage production.