Installing Sub-panel in garage for 30 A 220 volt receptacle.
#1
01-27-14, 06:11 AM
Installing Sub-panel in garage for 30 A 220 volt receptacle.
I am installing a sub-panel in my detached garage which is 50’ from the 100A main panel in the house. Currently, the garage is fed from a 15A circuit breaker with 14-3 + gnu through a buried 1” rigid conduit. The garage has lights, receptacles and a garage door opener. The main panel has an unused 30 A 240V breaker for a dryer which is unused. I will change that to a 60A 240V circuit breaker to feed the sub panel. The garage circuits could draw no more than a maximum of 30 to 32A. I am feeding a junction box at the end of the buried conduit with 6-3 cable. I am connecting in the junction box to #6ga THWN wire;(Red,Black,White,Green) with #6ga rated twist connectors,taped. At the garage, the 6ga wires will continue in 3/4” met conduit to a 60A Square D non-fusible disconnect switch and from there to the sub panel. The existing garage circuits will then be fed through 15A and 20 A circuit breakers. The main reason for the sub panel is to then add a 240V receptacle for future use. In addition to the 15A and 20A circuits, a 40A circuit breaker will feed the 240V receptacle. The sub panel will of course, have an isolated neutral bar and a separate ground bar bonded to the sub panel. The sub panel will be grounded with #6 bare wire to 2 8’ grounding bars outside of the garage. That is the technical layout of the project which I would like comments on. On a practical level, I am worried about pulling the 6ga wire through the 50’ conduit from the house. Any suggestions and experiences with pulling wire would be appreciated. I am planning on using the existing 14ga wire in the conduit to pull the 6ga wires through. I was thinking of changing all of the 6 ga wire to #8 ga to make it easier to pull. Would that make any sense or be legal. I have been to several other forums without getting satisfactory answers. Project is eminent, so any comments would be appreciated.
#2
01-27-14, 06:54 AM
Member
Are you planning on reusing the existing 1" rigid metallic conduit? You indicate you want to use the existing circuit to pull the new wire in, but you also indicate pulling in 4 - #6 conductors into a 3/4" conduit. How old is the existing rigid conduit? Is it rigid heavywall threaded conduit or is it EMT (thinwall)? You don't need a full #6 ground, you can use a #10 green insulated ground. The new conductors should include a white neutral in addition to a black and red (or another color) hot conductors.
#3
01-27-14, 07:12 AM
Thanks for the timely reply. The buried conduit from the house is 1” rigid metallic conduit. It now contains 14-3 wire feeding the garage. I plan on using the 14-3 wire to pull the 6ga through the buried conduit. Needless, to say, I’m worried about the difficulty of this operation. Someone told me about some finger-holding type device to hold the wire. I already have purchased the wire(red,black,white and green insulated). If it makes that much difference on the pulling, I could exchange the green #6 for 10g a. The 3/4” is met for inside of the garage. No problem with that part of the job. BTW, I assume the insulated green goes to the sub panel, but bare(I have #6ga), will go to two outside 8’ grounding rods. I look forward to further comments. I might mention, I’m really worried about getting halfway through the conduit pull and the wire getting hung up. I definitely in this weather not having to dig up the conduit. I’m in blow zero Ohio. 
#4
01-27-14, 07:16 AM
Group Moderator
You would not need a disconnect switch if your sub panel has a main, or you back feed a breaker.
You would not be required to run a ground in the steel pipe if it is rigid conduit. (EMT is not allowed to be buried) You should install grounding bushings on both ends and run a ground wire to the steel box on both ends.
If the pipe is not corroded inside the wire should go in OK. However I suggest pulling a pull wire/string/rope in when you pull the old cable out. I would not fight the old cable. Have a helper to pull while you push the new wire in. If you did change the wire to #8 inside the conduit you would be limited to 50 amps. The cable would still need to be #6.
If it was me, I would keep everything #6.
Google pulling grip. I believe Big orange has them. You will need a 3/4" one
You would not be required to run a ground in the steel pipe if it is rigid conduit. (EMT is not allowed to be buried) You should install grounding bushings on both ends and run a ground wire to the steel box on both ends.
If the pipe is not corroded inside the wire should go in OK. However I suggest pulling a pull wire/string/rope in when you pull the old cable out. I would not fight the old cable. Have a helper to pull while you push the new wire in. If you did change the wire to #8 inside the conduit you would be limited to 50 amps. The cable would still need to be #6.
If it was me, I would keep everything #6.
Google pulling grip. I believe Big orange has them. You will need a 3/4" one
#5
01-27-14, 07:35 AM
TNX. Great idea about the pulling rope. The buried conduit is 1” rigid conduit. How will I connect the 4 #6 wires to the pulling rope. Won’t that make a large bundle at the connection point? Too large for the 1” conduit. I got the suggestion before to change the green 6ga grounding wire to smaller 10 ga. Do you think that would make the pulling any easier?
#6
01-27-14, 08:59 AM
Group Moderator
It would really depend on the condition of the conduit. In new pipe I can push 50'+ alone with little problem. Have you pulled out the old cable?
Is this rigid steel or PVC? 4 - #6 wires is fairly small compared to 1" conduit. When I say rope, I'm thinking 1/4" paracord type stuff. A pulling grip would help, as would a helper.
You can get:
7 - #6 wires in a 1" RMC
6 - #6 wires in a 1" PVC
IF you can't get a grip, you can drill a small hole in the wire and insert some wire to from a loop. Twist each loop together to form one twisted loop. Tie the rope to the final loop. #6 is kind of small to do this, but it might help you in a pinch.
Is this rigid steel or PVC? 4 - #6 wires is fairly small compared to 1" conduit. When I say rope, I'm thinking 1/4" paracord type stuff. A pulling grip would help, as would a helper.
You can get:
7 - #6 wires in a 1" RMC
6 - #6 wires in a 1" PVC
IF you can't get a grip, you can drill a small hole in the wire and insert some wire to from a loop. Twist each loop together to form one twisted loop. Tie the rope to the final loop. #6 is kind of small to do this, but it might help you in a pinch.
#7
01-27-14, 09:31 AM
Not an expert on pulling wire but I'd strip 8" of insulation off of the wires. Then wrap wire 2 around wire 1 starting two inches down from the end of the insulation on 1 and then 3 four inches down from the end of the insulation on one and the smaller ground six inches down. Make a loop for the rope at the top of one. Wrap with one layer of electrical tape. Of course use lots of wire lube.
#8
01-27-14, 11:12 AM
installing sub panel in garage for 220 volt receptacle
The conduit is rigid steel, 18” deep, about 15 years old. This is all preplanning before I get started so as to not get caught unprepared in the middle of the job. Comments so far are great. Any comments so far on the technical aspects of the project. I’ve tried to stay compliant with NEC code as much as possible. To recap, 60A 240 breaker in main box, to 60A non-fusible disconnect box in garage, to sub panel in garage with 15and 20amp breakers to receptacles and general lighting and 40 amp breaker to 30A 240 receptacle. Sub panel box grounded to 2 8’ ground rods. Hope I’m on the right track.
Last edited by Chuckjq; 01-27-14 at 11:14 AM. Reason: left out word
#9
01-27-14, 11:40 AM
Group Moderator
40 amp breaker to 30A 240 receptacle.
Everything else sounds fine.
Any reason you are using the disconnect and not just feeding your subpanel as I mentioned earlier?
#10
01-27-14, 02:36 PM
installing subpanel in garage
I was under the impression from other forums that if a sub panel is in a separate structure, there must be a disconnect within sight of the sub panel for safety reasons according to the NEC. As I don’t have a copy of the NEC, I took there word for it. Already purchased it, but I do wonder now whether it was necessary.
Last edited by Chuckjq; 01-27-14 at 02:40 PM. Reason: misspelling word
#11
01-27-14, 02:41 PM
Group Moderator
You do, but the disconnect can be in the sub panel as a main breaker (does not matter if it is higher than the 60 feeding it, it is only a disconnect) or as another breaker that is back fed (#6 wires go to the screws on the breaker which in turns feeds the buses of the panel.)
#12
01-27-14, 02:49 PM
I was under the impression from other forums that if a sub panel is in separate strutter, there must be a disconnect within sight of the sub panel for safety reasons
If you already have a main lug only panel with more then six spaces you can install a branch circuit breaker equal to or greater then the house breaker and back feed it from the house by connecting the feed to it. (Must have a hold down kit installed.)
#13
01-27-14, 02:51 PM
sub Panel disconnect
TNX. I’ll go ahead and use it since it wasn’t very expensive. I believe there are two kinds of electrical panels; one with a main breaker disconnect and then the one I purchased which doesn’t have a main disconnect but the feed wires go directly to the switch hot busses. Thanks for all the help. I think I’m ready to go.
#14
01-27-14, 02:57 PM
the one I purchased which doesn’t have a main disconnect but the feed wires go directly to the switch hot busses.
If you already have a main lug only panel with more then six spaces you can install a branch circuit breaker equal to or greater then the house breaker and back feed it from the house by connecting the feed to it. (Must have a hold down kit installed.)
