conduit question for garage

[Chris Friesen]

I'm purchasing a house with an attached garage, and will be adding a subpanel for use as a shop. The garage is already insulated and drywalled, so I'll be running conduit (most likely EMT).

The most-filled run will have three 20A 120V circuits for outlets wired with #12, and 2 30A circuits for 240V wired with #10. (One 240V for the dust collector, and one for everything else.)

I'm currently planning to run a single #10 ground wire (bare or green) to ground everything on this run. I think this meets code, but I'd like confirmation.

Assuming the above is okay, I'll have 11 wires in that conduit. Given that I'm allowed 11 #10 wires in a 3/4" conduit, does that sound like a reasonable conduit fill? Max spacing between conduit openings will be about 10 ft.

Since this is a one-man shop I'll only ever be using two tools at once, maybe three if someone is helping. I'm working on the assumption that my load diversity is enough that I can use the 70% ampacity derate for

10 conductors. Is this reasonable, or do I have to go down to the 50%? Should I go with two 1/2" conduits instead of a single 3/4"?

Finally, what's the best way to pull this given that the various wires are going to different places, and one of the 240V circuits is going right to the end? Do I pull one section at a time with all the wires for that section?

Thanks,

Chris

[James "Cubby" Culbertson]

First off, I'm not an electrician. The specifics of conduit fill and such I would personally refer to the NEC codebook to verify. That being said, your wire sizes look ok to me. On the conduit, the fill may be fine but you'll find that pulling 11 wires through one 3/4" will be very tough unless all you have is a purely straight run. I would recommend at least 1" or break it up into two 1/2 or even 3/4 runs. As for pulling to various locations, I've found that you want to pull all your wires in at once and not try to finagle another set in after others have been pulled. I assume you'll be installing junction boxes somewhere along the run (keeping in mind you are limited as to how much bend you can have in the line without a box or other pull access....360 degrees if I remember correctly) so pull to the J-Box, route what you need out of the bundle then continue pulling the rest of the wires to the next J-Box. Not sure if this helps or confuses but good luck with it! Cheers, cc

[Tazz]

this wll help.

You dont mention if your 120v circuits wil be sharing neutrals. I am guessing it wont from the desrption. Also remember there is a derate for having that many current carrying conductors in a raceway

Insulation is factor.

40% FILL

[Terry]

You should ask this again at alt.engineering.electrical. Those guys can tell you more than you want to know over there. :)

[BobK207]

Chris-

Don't skimp on conduit size....your pulls will be easier with bigger conduit.

Also check box fills to make sure your boxes are large enough.....don't skimp on box sizes either.

cheers Bob

[Bud--]

With EMT and metal boxes you aren't required to run a ground wire, but if you do #10 is OK.

Using THHNs the wire fill is about 35%. Should be managable for 10 ft. Carefully avoid wire crossovers feeding the wire into the pipe.

You are (I assume)ignoring the ground wire to get from 11 to 10 which is correct. At 10 wires the derate is 50% - you aren't likely to use them all at once, but use in the future is unknown. If you ran a common neutral for 2 of the 20A circuits the wire count would be 9 (actually only 8 since the common neutral doesn't count) and the derate 70%. If using THHN wire in a dry garage the "ampacity" of #12 wire is 30 amps (but 20A max breaker). Using 70% derate the allowable current is 21A, so they can be on a 20A breaker. The "ampacity" of a #10 THHN wire is 40A (30A max breaker). Derated to 70% gives 28A - should be on a 25A breaker. If the conductor count is 6 or less, the derate is 80% which gives 32A for the #10s - can go on a 30A breaker. If the dust collector is hardwired the rules change.

Yes, pull all the wires in one run at the same time. Lot less mess in the boxes if the wires unused in that box loop through without splice (but harder to pull). I agree with Bob - box fill with that many wires is another thing to watch.

bud--