NEC 2008 Art. 408.36 interpretation!

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Fellows,
We have a conflict regarding 408.36 and panelboards side by side being fed by a feeder. One gent says if TWO panelboards are side by side w/ feed-thru listed bus and in/out lugs, that a separate OCPD be provided from one of these panels to the other to meet req's of this article. The other team says the downline feeder OCPD is satisfactory as long as the SAME SIZE wire is used to supply the other panelboard. Then the Question arises if the second panelboard were located say on another floor, could the feed thru be allowed without another OCPD from Panel 1 to Panel 2. (Side by side is "Grouped", but on a
different floor is no longer grouped!)
Your thoughts?
Byron L. Head, CEI, Omaha, NE
 

charlie b

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The wires don't have to be the same size (they just have to have enough ampacity), and the word "grouped" does not appear in 408.36. But a single breaker upstream of the first panel can protect both the first panel and the second (feed-thru) panel, even if the second panel is on another floor. The only requirement is that every panel be protected by an overcurrent device that is either within the panel or on its supply side. The feeder breaker serving the first panel is, indeed, on the supply side of the second panel.
 

iwire

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As long as the overcurrent device at the feeders origin has rating of, or below the panels ratings no mains are required in any panel grouped or not.
 
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Thanks! Now - One more question.

Thanks! Now - One more question.

Sir Charles, your EE answers are, as always spot on amd clearly stated.

Now this: You can feed - say, a 400a 3ph 4w 208v panelboard with
500mcm CU. CAN you feed that panel with TWO 2" raceways with
4 - 3/0's CU (ea) to the double input lug set, VIA (by way of): 2 - 200A
OCPD's??? Legal?

Thanks
 

augie47

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State Electrical Inspector (Retired)
Sir Charles, your EE answers are, as always spot on amd clearly stated.

Now this: You can feed - say, a 400a 3ph 4w 208v panelboard with
500mcm CU. CAN you feed that panel with TWO 2" raceways with
4 - 3/0's CU (ea) to the double input lug set, VIA (by way of): 2 - 200A
OCPD's??? Legal?



Thanks

simplist way to answer may be by Code quote:
240.8 Fuses or Circuit Breakers in Parallel.
Fuses and circuit breakers shall be permitted to be connected in parallel where they are factory assembled in parallel and listed as a unit. Individual fuses, circuit breakers, or combinations thereof shall not otherwise be connected in parallel.
 

charlie b

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Lockport, IL
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Retired Electrical Engineer
Now this: You can feed - say, a 400a 3ph 4w 208v panelboard with 500mcm CU.
Says who? Show me a load calculation that declares the demand load to be 380 amps or lower, and I will agree. Show me a load calculation that declares the demand load to be between 381 amps and 400 amps, or tell me that there is no load calculation, and I will disagree.
CAN you feed that panel with TWO 2" raceways with 4 - 3/0's CU (ea) to the double input lug set, VIA (by way of): 2 - 200A OCPD's???
Not legal, as Gus has already pointed out. But let me add that it was legal (presuming there were lugs on the first panel capable of handling that particular pair of sets of conductors) until you got to the ?2 OCPDs? part.
Sir Charles, your EE answers are, as always spot on and clearly stated.
You are too kind. And the title is ?Sir Knight,? by the way, and I don?t use it here. ;)


 

augie47

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Tennessee
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State Electrical Inspector (Retired)
I might add to Sir Knight's comment on your 500's feeding that 400 amp panel that not only would I want to see a load calculation, but regardless of the load, if those conductors were transformer secondary conductors installed be Art 240, 500 kcmil would not be acceptable {240.21(C)}
 
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