branch circuit sizing

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ajengin

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Can a MDP with a main breaker rated at 400 amps and have a branch breaker with 400 amps? Is this possible

Current SItuation:
400 amps incoming service into an MDP rated for 400 amps. There is a water heater that needs to be powered off this but the breaker needed is 400 amps. Is there anywhere in the NEC says that this is not possible?
 
Re: branch circuit sizing

The connected load of the occupancy determines the requirments the service has to meet. How does the rest of the load, other than the water heater, add to the load of the water heater by the NEC?
 
Re: branch circuit sizing

THE ISSUE IS MORE RELATED TO THE BREAKER SIZING RATHER THAN THE SYSTEM LOAD. THE LOAD IS FINE... ITS JUST THAT THIS WATER HEATER NEEDS A 400 AMP BREAKER.
 
Re: branch circuit sizing

Not usually. I 400-amp rated panelboard will probably be limited to 200-amp branches or less. If this is to be a new panelboard you could probably order it with what is called a "subfeed" breaker. Basically the panelboard is modified to include a breaker, usually at the opposite end of the main that connects across the busses like the main breaker does. It would take up at least six of your branch circuit spaces though.

This is kind of a weird situation. What else is connected to this panelboard? Are you sure that 400 amps is a sufficient service size?
 
Re: branch circuit sizing

I'm curious how much current the water heater actually uses and why in the world it needs a 400 amp breaker.

Edit: And does it need 600 MCM conductors?

[ March 08, 2005, 11:26 AM: Message edited by: physis ]
 
Re: branch circuit sizing

ajengin, [sensitive al]were you really shouting your reply?[/sensitive al]

I just put in a "feed thru" service disconnect and load center panel. 200 A service disconnect connected to bus bars with 16 poles for branch circuits. The bus bars end in factory lugs that permit the extension of the 200 Amp capacity of the service disconnect to a feeder that I ran to a subpanel.

This is a smaller scale of what you are asking after.

The question you are asking is somewhat like the classic do-it-yourself inquiry about "can the sum of the breaker handle amp ratings be bigger than the service disconnect breaker?"

It's really about the connected load.
 
Re: branch circuit sizing

i was not shouting at all. I happened to be in caps when I was working in Autocad. sorry
 
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