Home run or separate ?

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  #1  
Old 03-23-05, 06:37 AM
KVacek
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Home run or separate ?

I'm remodeling the kitchen, running two 40-amp circuits plus a few more 15-amp and 20-amp utility circuits.

Code here is metallic conduit - no NM, Romex, etc.

Because of the relatively difficult path from the breaker box in the garage to the central core of the house, through two small roof areas, etc., I have long planned to put in a "home run" of 2" EMT and 4" square duct, to make running whatever I need now or later much easier.

I've heard of people putting in a "home run" on occasion and no mention of any restrictions beyond conduit fill.

An old electrician friend said it was a lot of work (he has no idea how hard it is to run 1 conduit through that path), but it would be legal. He mentioned a restriction for new work of 9 current-carrying conductors, but said it didn't apply to remodeling (?!).

After having much of this in place (no wires yet though) I was leafing through the NEC and suddenly thought about the derating when more than 3 conductors are used.

Stupid me - for 40 years I've occasionally gone over that, (home and industrial - mostly for myself and my businesses) and no inspector has ever mentioned any problem. And one job was part of a school, and it was inspected pretty thoroughly by a guy who hated non-union (me) workers. Is there some loophole that says derating doesn't apply, or have I just been wrong all along ??

I can upsize wires ($$) or I can just abandon this plan (and my 2" EMT already bent and installed) and run say three 3/4" EMT's and be done for now.

Thanks!
Karl
 
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  #2  
Old 03-23-05, 06:46 AM
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In addition to conduit fill, you must also be concerned about ampacity derating. For circuits up to 30 amps, the rule of no more than 9 current-carrying conductors in any one raceway (conduit) is a handy rule of thumb. Although you are correct in that derating starts at 3 conductors, it usually doesn't force a breaker size reduction (or a wire size increase) until the number gets to 9.

For larger circuits, the rule of 9 may not apply. So you need to actually compute the ampacity according to NEC rules. Bottom line is that multiple smaller conduits side-by-side is often a better solution than one larger conduit.

The rules apply equally to new construction and remodels.

Do the calculations with your actual numbers and then you'll know what to do.
 
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