Garage Subpanel (Cable vs. Conduit)

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Old 09-02-09, 06:45 PM
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Garage Subpanel (Cable vs. Conduit)

I have to give a thanks for that reply also. I have been looking into putting a subpanel in my garage and that answered almost all the questions i had. I did say almost. I have one question to add. I will be running 3 #6 and 1 #8 ground THHN/THWN dual rated wire from my house panel to the sub panel in the attached garage. I dont want to cut the wall where my existing panel is to get conduit into the box. I can probably fish some cable in there. If i set a box under the panel and transition from the THHN/THWN to cable, do i have to have a cable with 3 #6 wires and a #8 ground? My local stores dont have that. Could i run a regular 6/3 cable and another cable with 1 #8 for the ground? Could i run the 6/3 cable and just continue on up the wall with the #8 THHN/THWN from the conduit for the ground (This doesnt sound right to me but i thought i would ask anyway. So what are my options? Sorry for another long post.
 
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Old 09-02-09, 08:52 PM
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I don't recommend the transition to cable for the last few feet simply because the cable has a lower temperature rating than the THHN, so your entire run will be constrained by the few feet right below the box. It's the weakest link in the chain.

If you can fish a cable into the space, you can probably fish some flexible conduit to just run THHN the whole way. It's really a much better installation with a continuous cable from panel to panel (no splices).
 
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Old 09-03-09, 05:41 AM
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I see your point there. The reason i thought about doing it this way was by looking at some garage installations but they were not attached. The recommended install consisted of cable from the main panel in the house to a box at the end of the house. Then transitioned to THWN on out to the barn/garage. I just assumed the same install would work in reverse. What type of Flexible conduit do you recommend, and in what size? Its only going to be like a 5 foott piece into the box.
 
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Old 09-03-09, 07:54 AM
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There is also a Sticky Note at the top of the topics list which shows a variety of both past and current configurations for subpanel installations.
 
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Old 09-03-09, 11:46 AM
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I had already looked over the Sticky. I have the procedure and what wires i need pretty much down. Could i use the blue (smurf pipe) flexable conduit to go from the junction box up into the main panel? 3/4 smurf pipe is the largest flexable conduit that my local lowes sells. Could i put 3-#6 and 1-#8 in 3/4 smurf? Again its only 4 to 5 feet. If you cant do that could i run say the two hot legs in one, and the neutral and ground in another, and just take two of the 3/4 smurf pipes up into the box?
 
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Old 09-03-09, 11:50 AM
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I will need to check the chart to see if that all will fit in a 3/4 ENT.

I will tell you that you cannot split it into the 2 ENT runs like you describe.
 
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Old 09-03-09, 11:58 AM
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What size of service are you planning to run.

Jim
 
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Old 09-03-09, 01:31 PM
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The sub panel in the garage will be fed off a 60 amp breaker in the main box. Thats pretty much the max for #6 feed right? Do they make bigger smurf pipe and i need to go to an industrial place to get it? Why cant i split the wires and run two, is it a safety issue or is it a code issue?
 
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Old 09-03-09, 02:05 PM
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Originally Posted by mud4me View Post
The sub panel in the garage will be fed off a 60 amp breaker in the main box. Thats pretty much the max for #6 feed right?
60A is the max for a #6 cable, 70A for #6 conductors in conduit but you would need to bump the ground up to #8 in that case.

Do they make bigger smurf pipe and i need to go to an industrial place to get it?
They make it up to 2", but you'll have to call around to supply houses to find sizes above 3/4". You could also use flexible metal conduit if ENT is not available in your area.

Why cant i split the wires and run two, is it a safety issue or is it a code issue?
Kinda one in the same, right? The issue is that all conductors of a circuit must run in the same conduit. The good news though is that three #6 plus one #10 can fit in a 3/4" conduit.
 
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Old 09-03-09, 02:49 PM
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I had planned on running a #8 ground anyway because i already have the wire and it was free so thats what i was going to run. I guess the last question i have is will the 3 #6 wires with the #8 ground fit in a 3/4 conduit? I already have the 3/4 ridgid pvc conduit but that can easily be exchanged for 1" conduit if need be. Thanks for all the help guys. I plan on putting this in over the weekend.
 
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Old 09-03-09, 03:08 PM
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They will fit in a 3/4" rigid PVC or a 3/4" flexible metal, but not in a 3/4" ENT. With the #8 ground you are also free to go up to a 70A breaker if you wish.
 
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Old 09-03-09, 08:17 PM
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Thanks for all the replies, this is the first time i have used this forum but it looks like i will be back :-). Everyones help is greatly appreciated. Now i have to go run some conduit and tell the wife i HAD to put the sub panel in because it was alot safer, or code or something .
 
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