Is this NEC violation?

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anbm

Senior Member
Location
TX
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Designer
I saw this installation in one of existing building.

Distribution panel 'A' (800A MLO, 480Y/277V), one of its CB is 400A breaker and feed panel 'B'.

Distribution panel 'B' is rated at 400A MLO, 480Y/277V and contains these branch breakers:

400A
200A
100A

Even panel 'B' is not overloaded, will 400A breaker in panel 'B' be acceptable? Because panel 'B' is also fed out of a 400A breaker in panel 'A'. For coordination purpose, this installation doesn't work.
 
In those installations that do not require selective coordination (and that is most of what we deal with), it is certainly acceptable to have one 400 amp breaker downstream of another.
 
Not a Code Violation.

As long as the conductors are rated for the calculated load.

As far as the Code is concerned, the equipment connected to the 400 amp breaker may only operate on Monday. The equipment connected to the other breakers never operate on Monday.
It is what the CMP folks like to call a "design issue", not a "Code issue"
 
I would first ask what type of facility you were in (hospital?) and what branch of the electrical system was it that you were looking at. Selective coordination is required for emergency systems, legally required stand-by systems, essential electrical systems, and certain elevator installations.
 
Since 2008, NEC 700 and 701 no longer require selective coordination between two 'identically sized' devices in series with no other devices or loads between them.
 
That's true, Jim. But in this particular case, the two 400 amp breakers are not in series.
 
I have not worked on many of these larger panels but in the smaller residential panels you generally can't install more than a 125 amps on the buss of a 200 amp panel. I would check to make sure the panel is suitable for a 400 amp breaker connected to the buss.
 
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