Feeders From Substation Breaker

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Jim W

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We have a installation that has a 1600amp substation breaker with 4 sets of 500 kcmils feeding 2 seperate 800 amp fused switches. 2 sets of 500 kcmil feed switch 1 and 2 sets of 500 kcmil feed switch 2 from the 1600 amp breaher directly. Both switches are fused at 800 amps.
The question is can you split the service entrance conductors into 2 sets each and feed 2 seperate loads directly from the upstream breaker?

What section of code is this acceptable or unacceptable???
 
Jim W said:
We have a installation that has a 1600amp substation breaker with 4 sets of 500 kcmils feeding 2 seperate 800 amp fused switches.
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This is a violation of 240.4C. 4 500 kcm has an ampacity of 1520 amps.

Jim W said:
2 sets of 500 kcmil feed switch 1 and 2 sets of 500 kcmil feed switch 2 from the 1600 amp breaher directly. Both switches are fused at 800 amps.
The question is can you split the service entrance conductors into 2 sets each and feed 2 seperate loads directly from the upstream breaker?

What section of code is this acceptable or unacceptable???
Click to expand...
If I am reading your post correctly you are tapping 2 of the 500 kcm which is only half of the feeder. 240.21B allows you to tap the feeder not half a feeder. You should connect to all 4 of the conductors.(needs to be 4 600kcm)
 
Bob:

Since he is feeding two separate 800A breakers, I think the 500KCM wire is OK. (That is, if I understand correctly. I think he wants a 1600 amp breaker to feed 4 sets of 500, with 2 sets of 500 feeding one 800A breaker, and 2 sets feeding another 800A breaker. Still a tap, but tapped right onto the 1600A breaker.)

This might be OK, or it might not. It will depend on the load, the length of the run, and where it is (inside or outside for example). See the tap rules in 240.20(B) if this is under 600V and the substation is not part of the utility.
 
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Steve,
The tap rules require that the tap conductors be protected at the load end at or below their ampacity. You are not permitted to use 240.4(B) to round up the protection. The parallel 500s need an OCPD of 760 amps or less.
Don
 
Ragin Cajun said:
How about using 600 MCM instead of 500 MCM? Each 600 MCM is good for 420A and two would be well protected by an 800A breaker.
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That would work. As Don said the tap conductors need to be rated for the full ampacity or higher. Rounding up is not permitted.
 
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