Can I run 4/C 500A to 2, 2/C 250A breakers?

mayanees

mayanees

Senior Member
Location
Westminster, MD
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Electrical Engineer and Master Electrician
The question is, can I run 4 conductors from a 500-amp circuit breaker, and terminate 2 of the conductors on one 250A breaker, and 2 on the other?

Thanks
 
infinity said:
Yes but the tap rule in 240.21 would apply.
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If the conductors are size for the 250A breakers, rather than the 500A breaker. Which of course would be more economical.

Assuming all the breakers are double pole, so the 4/C represents two sets, if the two 250A breakers are near other but far from the 500A breaker, then you could shorten the tap distance by recombining the two sets before splitting them off to the two different 250A breakers. That way the run between the 500A breaker and the recombination point is not a tap, it has a 500A ampacity (or somewhat less if using 240.4(B)).

Cheers, Wayne
 
wwhitney said:
If the conductors are size for the 250A breakers, rather than the 500A breaker. Which of course would be more economical.

Assuming all the breakers are double pole, so the 4/C represents two sets, if the two 250A breakers are near other but far from the 500A breaker, then you could shorten the tap distance by recombining the two sets before splitting them off to the two different 250A breakers. That way the run between the 500A breaker and the recombination point is not a tap, it has a 500A ampacity (or somewhat less if using 240.4(B)).

Cheers, Wayne
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There is one, 480Volt, 500-amp, 3-pole breaker that powers two 250A, 3P breakers 150 feet away with 4/C 125A (for a summation of 500A) cable. I thought I might go to a tap box, then come out to the two 250A breakers, but now I think the direct method seems appropriate to the NEC. That's my question.
 
mayanees said:
the 500-amp, 3-pole breaker is 150 feet from the two, 250A breakers.
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The answer is no. You would have to run the 500 amp feeder within 25' of the two 250 amp breakers and tap it there unless these conductors are all on the outside of the building.
 
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Since I have the finest minds on the internet for free what is the minimum conductor size could be hooked to 200 feed thru lugs on single phase?
 
Ok, this would be dwelling. It might be distance too? I rarely use taps,, I am aware but just dont have the app. I would say 6 is too small by a pinch? Thanks, I was kind of hoping you were the man to answer.
 
Sberry said:
Ok, this would be dwelling. It might be distance too? I rarely use taps,, I am aware but just dont have the app. I would say 6 is too small by a pinch? Thanks, I was kind of hoping you were the man to answer.
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A few options for the feed through. You can use the same size as the service conductors even if they've been sized at 83%. That could mean #2/0 copper or #4/0 aluminum. If you can comply with the 10' or 25 ' tap rule then you can use smaller tap conductors. Obviously there are many variables depending on your exact installion parameters.
 
The way I ask may be vauge. I have an inspecta bud and I ask on occasion and he rattles off 2 or 3 sections and 40 yrs ago I memorise that its a 6 to a rod and wouldnt have any idea how to calculate it,,, or really care. I like to be "aware" so to speak. I was on a job 20 yrs ago and notice something that I had read on a forum and said,,, whoa,,, not likely the right breaker. I didnt know exact but some gut shot numbers didnt make sense.
 
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Only reason I had thought of this was I saw a 8 space feed thru that was full and they wanted to feed a garage, I believe 2 alum is legal to hook to these lugs if we limited the breaker downstream? The guy has seen a 100 on the 2 and I said, no, limited to 90 so a 100 main in the second was no good.
 
Sberry said:
Only reason I had thought of this was I saw a 8 space feed thru that was full and they wanted to feed a garage, I believe 2 alum is legal to hook to these lugs if we limited the breaker downstream? The guy has seen a 100 on the 2 and I said, no, limited to 90 so a 100 main in the second was no good.
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Do you have an electrician to perform this work? It sounds like you're entering into DIY territory.
 
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