400 amp breaker question?

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mark29309

Member
Location
New Orleans
I am installing feeders to a new motor control center. We have a 400 amp main breaker panel, and I want to install an additional 400 amp sub feed breaker to feed the MCC.

The engineer is telling me that I need to install through feed lugs and a disconnect. He said he is looking to see if I will be able to install the breaker.

Is there anything in the code that would prohibit me from installing the 400 amp sub feed breaker.
 
We know the load . It’s 319 amps. He said he is checking to see if we can put (2) 400 amp breakers in the same panel. I don’t know.

Its all about the loads - you can put 37 400 amp breakers in a 400 amp panel if it meets nec load calcs. There may be an issue with a given frame size physically being able to fit and mount in a given panelboard, perhaps that it what he is looking into.

Feed thru/sub feed lugs are a good option if they are available for that panelboard and would save the cost of the breaker. You dont even need a disconnect, unless the conductors are a tap (rated less than next standard size down from 400).
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
We know the load . It’s 319 amps. He said he is checking to see if we can put (2) 400 amp breakers in the same panel. I don’t know.
If you have almost no other loads on that 400A panel, no problem... but is that the case? In other words if the bus bars are rated for 400A and the main is rated for 400A, adding feed through lugs doesn’t change that scenario. It remains a 400A circuit that you are adding 319 A to and you have very little head room there.
 

kwired

Electron manager
Location
NE Nebraska
Details of the panel in question may help determine if you can even install a 400 amp breaker in it, or if sub feed lugs are even an option for it.

That said if no other load is to be supplied by the panel, might be simplest to just put in a 400 amp single breaker enclosure or 400 amp fused switch, might even cost less.
 
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