Mutiple main breakers in same panel box

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dpisfty

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Situation:

A customer has two machines. One has a 240volt single phase motor and the second a 480volt 3 phase motor. He would like to install the breakers for these motors in the same pannel. They are the only two breakers in the pannel and there would be no further additions to the pannel. My questions are as follows:

Is this an allowable procedure?
and-
Regardless of the answer, where can I find the supporting documentation?

Thank You
 
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I don't understand the questions. But I think it is because you are using the phrase "main breaker" incorrectly.

A "panel" consists of a set of bus bars that are energized from some upstream source. You insert braekers in the panel to supply power to loads downstream. A panel may or may not have a single "main breaker" (within the same enclosure) that can turn off power to all the bus bars at the same time. If it does not, then power to the panel must be turned off through some breaker, fuses, or disconnect switch further upstream.

You cannot energize a panel's singe set of bus bars from two different places. A panel may have one main breaker, or none, but not two.
 
This may or may not be off topic, but just the other day I noticed 408.36 (2005 NEC), which says in part

"Each lighting and appliance branch-circuit panelboard shall be individually protected on the supply side by not more than two main circuit breakers ... having a combined rating greater than that of the panelboard."

The question looks to me like a test question, and maybe this is what they were looking for, but I'm not sure of the circumstances where you would need to do this. I guess you could have a situation where the upstream equipment will not accept a single circuit breaker large enough for the panel load, and you might run two feeders to two main devices, but I've never seen anything like this.

Anyone know?

Matt
 
msb10 said:
This may or may not be off topic, but just the other day I noticed 408.36 (2005 NEC), which says in part

"Each lighting and appliance branch-circuit panelboard shall be individually protected on the supply side by not more than two main circuit breakers ... having a combined rating greater than that of the panelboard."

The question looks to me like a test question, and maybe this is what they were looking for, but I'm not sure of the circumstances where you would need to do this. I guess you could have a situation where the upstream equipment will not accept a single circuit breaker large enough for the panel load, and you might run two feeders to two main devices, but I've never seen anything like this.

Anyone know?

Matt
Click to expand...

That situation is explained on page 484 of the Handbook Exhibit408.3.
It shows a panel that is basically two separate panels built into one housing enclosure.

David
 
Pierre C Belarge said:
Did anyone notice he mentions 240V and 480V in the same panel enclosure????:confused:
Click to expand...

The easiest way to address that is with stickers 1 sticker will be 240 the other 480!
 
Pierre C Belarge said:
Did anyone notice he mentions 240V and 480V in the same panel enclosure????:confused:
Click to expand...

Yes. :)

I see 240 and 480 breakers in the same control enclosure often.

Not so often in the same panel enclosure.;)
 
It sounds to me like he is talking about NFPA 79 item. I am guessing he wants to have a main disconnect on the control panel and two molded case breakers on the inside. Labeled properly that shouldn't be a problem.
 
the other thing is that what the OP did mention both 240 and 480 system in there

I will just labeled " multi power source " or something like that so let them know have to deal more than one power system in the enclosre box

as long properly labeled i think it will be ok as Bob B saying that it do show up once a while

the same thing with me i did see it but not too often to see diffrent incomming voltage in the box as long it properly marked

Merci, Marc
 
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