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Old 10-12-2015, 12:30 PM   #1
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Yet another "subpanel in the garage." thread.


Hey all,
I'm kinda stuck on wiring a sub panel out to my garage. The garage is attached so all I need to do is run the wire through the floor trusses in the ceiling of my finished basement. I plan on routing the cable through the storage area under the stairs, so it will be exposed there. I am planning on a 100amp panel in the garage. (yes, I actually do need that much amperage as I'm running a 20hp phase converter for a 10hp metal lathe.) I've been doing a lot of research on the topic and my understanding is that I need three runs of #2 copper THHN wire. (two hot, one ground) but upon further research I found conflicting information on whether individual wire runs like this need to be run through conduit or not, and I've seen other people say I need 4 wires (which doesn't seem right given what the national code says.) Any help or advice on the subject would be helpful. Thanks.
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Old 10-12-2015, 12:36 PM   #2
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Quote:
Originally Posted by Ironman187 View Post
Hey all,
I'm kinda stuck on wiring a sub panel out to my garage. The garage is attached so all I need to do is run the wire through the floor trusses in the ceiling of my finished basement. I plan on routing the cable through the storage area under the stairs, so it will be exposed there. I am planning on a 100amp panel in the garage. (yes, I actually do need that much amperage as I'm running a 20hp phase converter for a 10hp metal lathe.) I've been doing a lot of research on the topic and my understanding is that I need three runs of #2 copper THHN wire. (two hot, one ground) but upon further research I found conflicting information on whether individual wire runs like this need to be run through conduit or not, and I've seen other people say I need 4 wires (which doesn't seem right given what the national code says.) Any help or advice on the subject would be helpful. Thanks.
You shouldn't need the four wires, and depending on length and exposure is if you'll need a conduit.
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Old 10-12-2015, 01:26 PM   #3
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You need 4 wires ( if you want any 120 volt loads) and individual conductors are required to be in conduit
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Old 10-12-2015, 01:28 PM   #4
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If your sub panel is going to supply both 120 and 240 volt loads, you must have 4 wires: 2 hots, a neutral and a ground. If you run individual wires, they must be in a conduit. You can also run a 4 wire cable without conduit, SER or NM for example.

If you are only supplying the 240 loads you can use 2 hots and a ground. But you can never have any 120 volt loads, like general purpose receptacles or lights.

If the phase converter is the only load, you do not need a sub panel. Wire the phase converter up directly.
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Old 10-12-2015, 01:32 PM   #5
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I read incorrectly as to your voltage, my apologies. You DO need the four.
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Old 10-12-2015, 01:32 PM   #6
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You shouldn't need the four wires, and depending on length and exposure is if you'll need a conduit.
You sir, should not be providing electrical advice. Both of your comments are wrong.
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Old 10-12-2015, 01:48 PM   #7
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You sir, should not be providing electrical advice. Both of your comments are wrong.
Just found out I can edit my comments. You are right my friend. I didn't read thoroughly and didn't fact check.

I'm sorry.
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Old 10-12-2015, 05:33 PM   #8
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Hey guys, thanks for the replies. It seems I've done so much research that I no longer have the confidence to know what is right and what isn't. So in essence I need to run conduit through my finished wall and my finished ceiling in the basement as well as the unfinished area under the stairs? Also, I've looked at so many tables I don't know which ones are what anymore. In reading chapter 6 of the NEC, I see that for feeder lines I need to use table E3605.1, which dictates that #3 copper THHN wire is good up to 110 amps. Furthermore table 250.122 states that a #8 copper wire is sufficient for grounding. Am I way off here because I've been reading everywhere else on the web that I need #2 CU for live and neutral, and #4 for ground. Thanks again.
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Old 10-12-2015, 06:31 PM   #9
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Does his conduit need to be emt? Could he run that gray soft flexible conduit? I think it is called seal tight.
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