Qty of breaker in a main entrance

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templdl

Senior Member
Location
Wisconsin
Re: Qty of breaker in a main entrance

Or you going to have an 4800a load? Then the service is too small. Ohterwise it would be based upon the diversity of the load which I believe that you will find will average well under 4000a and at its maximum may approach 4000a.
 
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cosmos

Member
Re: Qty of breaker in a main entrance

Panel itself doesn't need overcurrent protection, but it's ampacity does need to be sized for its load.
 
volt101

volt101

Senior Member
Location
New Hampshire
Re: Qty of breaker in a main entrance

230.90(A) Exception No. 3: Two to six circuit breakers or sets of fuses shall be permitted as the overcurrent device to provide the overload protection. The sum of the ratings of the circuit breakers or fuses shall be permitted to exceed the ampacity of the service conductors, provided the calculated load does not exceed the ampacity of the service conductors.
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Jim
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Re: Qty of breaker in a main entrance

I agree with volt101 and his reference.

All that matters is the calculated load in this case does not exceed 4000 amps.

This set up puts much more responsibility on any electricians adding load to the service to ensure the total of 4000 is not exceeded.
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Re: Qty of breaker in a main entrance

iwire, (and others):
from your posts, it appears that, like myself, you have been to more of these rodeos than you wish to admit; so I'll ask: have you ever seen a problem from this situation ?

It has bugged me for years when I see commercial/industrial jobs with MLO service panelboards equipped with feeder OCP's that often
out-rate the panelboard and service conductors 2 or 3 times. I understand the legality, and have honestly never seen the "meltdown" that I have expected for years.

Guess its a compliment to our trade that many contractors watch for this as load is added, but I remain surprised there are not a number of service failures.

Your comments would be appreciated.
 
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