> Ok, here's one for the electricians....
>
> I have a great shop with marginal power and I need to upgrade.
> The shop is
> about 20 ft away from my main house panel which is a 200 amp service.
> Unfortunately the existing wire is four ~8ga runs from two 15amp
> breakers.
>
> The problem is that the wires run through a 1" conduit that's
> burried in a
> concrete slab. I really don't want to dig this up so I need to figure out
> the largest wires I can get through the existing conduit.
A quick Google turns up
http://bwcecom.belden.com/Catalog/Conduitcc/cncpchtp.htm
which says that a 1" diameter conduit is allowed (by the NEC) to have a
total of .35 in^2 of cable installed (with 3 or more cables).
Grainger has 2 AWG THHN wire listed at .381" od, which means 3 of them would
only take up .342 in^2
http://www.grainger.com/Grainger/productdetail.jsp?xi=xi&ItemId=1612704035&c
citem=
2 AWG THHN is rated for 130 amps in conduit (assuming your slab never gets
over 86F). If you don't have to pass inspection, you could probably get
away with 150 amp breakers at the house (but 125 would meet code). Then put
a sub-panel in the shop to split it up as needed.
However, don't forget you're robbing power from the house, and 200 amps is
none too big by today's standards. If you have high power electric devices
in the house (dryer, range, furnace, water heater etc.), you may have to
forgo using them while drawing 150 amps in your shop, or risk blowing a main
breaker.
If that's not big enough, you might be able to squeeze in (2) 1 AWG wires
plus a 2 AWG; which would get you a rated 150 amps. That's a code violation
(because the conduit is overfilled), but your inspector may overlook it.
Randall - not a licensed electrician
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