I like to do things right and if I don't know something I like to find the
answer in writeing but, I can find in writing that over 3 conductors in a
conduit must be derated in current capacity. I also have a reference that
says you can put, for one example, up to 12 #14 conductors in 1/2" EMT. So
in residential single family house wireing, how many #14 and #12 THHN wires
can I pull in 1/2" and 3/4" EMT and meet NEC code? Assuming half the wires
are hot and half are white neutrals.
When using different wire sizes, you have to do a calculation.
There are also considerations of whether the neutrals are
to be counted or not. Complicated question and no single, easy answer.
Do this GOOGLE:
I got 146,000 hits!
(This assumes you're using THHN (or similar) wire)
When applying the ampacity reduction for more than
3 conductors, note that you are allowed to use the
90C ratings in the table for THHN.
The easiest would be to look up how many #12's you can use and pretend
the #14 wires are #12. Otherwise you have to calculate the area of the
wires and the area of the conduit and not exceed whatever percentage
fill you're allowed.
BTW, as you approach the maximum allowed fill, it gets *very* difficult
to maneuver an ELB fitting or inside-corner elbow.
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