Generator Feeder and CB

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strap89

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Odd situation. I am looking at a set of 1 lines another engineer put together a few years ago. The generator breaker is sized at 1800A, the feeder is sized at 1200A and the downstream emregency distribution panel MCB is sized at 1200A. Any code violations here? I'm trying to find an NEC reference that states upstream and down stream breakers have to be the same rating. To me, it seems like the conductors are protected up to 1200A, regardless of the rating of the gen breaker...Thanks.
 
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strap89

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ron said:
How are the conductors protected at 1200A with an 1800A breaker? Does the 1800A breaker have an adjustable long time pickup setting?
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I am assuming downstream at the emergency distribution panel with a 1200A breaker. Panel is not MLO. No long time pick up setting on the gen breaker. I think it violates 240.4(C)
 
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copper chopper

Senior Member
Location
wisconsin
the first step in this is to find out what the nameplate rating on the generator is. 445.13 states that the conductor sizing shall not be less than 115 percent of the nameplate rating of the generator.from there we can determine whats right and whats wrong.

 
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copper chopper

Senior Member
Location
wisconsin
forget that last post I was thinking in the wrong direction..705.30 states to use article 240 for protection=240.4c is what your looking for ,also they could be tap conductors we need more info to see if this is legal.
 
augie47

augie47

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Tennessee
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State Electrical Inspector (Retired)
To me, it's all summed up in 240.21.
Your basic rule is that the conductors be protected at their ampacity at the supply.
The secret then would be to see if your install meets any of the "except as" situations.

The one possibility I see is 240.21(C)(4) if you meet those parameters.
 
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Worlds Gr8est Electrician

Member
augie47 said:
To me, it's all summed up in 240.21.
Your basic rule is that the conductors be protected at their ampacity at the supply.
The secret then would be to see if your install meets any of the "except as" situations.

The one possibility I see is 240.21(C)(4) if you meet those parameters.
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Yeah but wouldn't the conductors be protected at 1200 amps since if the load is greater then 1200 amps it would trip the 1200 amp breaker before it ever exceeded the rating of the wire.
 
iwire

iwire

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Location
Massachusetts
strap89 said:
The generator breaker is sized at 1800A, the feeder is sized at 1200A and the downstream emergency distribution panel MCB is sized at 1200A. Any code violations here?
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Hard to say without more details but in my opinion there is a small chance the installation could be allowed with 240.21(B)(5)



240.21(B)

(5) Outside Taps of Unlimited Length. Where the conductors
are located outdoors of a building or structure, except
at the point of load termination, and comply with all of
the following conditions:

(1) The conductors are protected from physical damage in
an approved manner.

(2) The conductors terminate at a single circuit breaker or
a single set of fuses that limit the load to the ampacity
of the conductors. This single overcurrent device shall
be permitted to supply any number of additional overcurrent
devices on its load side.

(3) The overcurrent device for the conductors is an integral
part of a disconnecting means or shall be located immediately
adjacent thereto.

(4) The disconnecting means for the conductors is installed
at a readily accessible location complying with one of
the following:

a. Outside of a building or structure

b. Inside, nearest the point of entrance of the conductors

c. Where installed in accordance with 230.6, nearest
the point of entrance of the conductors
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don_resqcapt19

don_resqcapt19

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Location
Illinois
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retired electrician
flytyingyaker said:
Yeah but wouldn't the conductors be protected at 1200 amps since if the load is greater then 1200 amps it would trip the 1200 amp breaker before it ever exceeded the rating of the wire.
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The conductors are not protected at their ampacity at the power source as required by the rules in Article 240.
 
don_resqcapt19

don_resqcapt19

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Staff member
Location
Illinois
Occupation
retired electrician
flytyingyaker said:
The other day I feed a 200 amp main breaker panel from a 150 main at the meter. The load could not exceed the 150 amps. Seems the same as your situation just with a generator.
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And you connected 150 amp wire to the 150 amp breaker at the power source...those conductors are protected at their ampacity. With the generator we connected 1200 amp wires to the 1800 amp breaker at the power source....these conductors are not protected at their ampacity.
 
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