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Old 06-26-2009, 01:59 PM   #1
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A few slightly different questions on subpanel wiring.


Hello,

I have a few questions regarding my plans to put a 60amp subpanel in my detached garage. I realize this is a very popular topic and have done my best to search for answers in this forum before asking.

My plan is to run ~ 30ft of 6-3 romex (protected in walls and joists) from the main panel in my basement to a PVC junction box inside the basement where I will transition to 3 separate 6 gauge THWN2 cables & a 10 gauge THWN2 ground cable (~ 35 ft). The THWN2 cables will be protected in 1 1/4" PVC conduit and run down the wall, into a trench 18" deep to the garage where it comes up and goes inside the garage stud bay to the subpanel.

The plan is to hook up a 60amp breaker in the main panel at the house (its a GE panel) and I purchased a Square D main lugs subpanel for the garage. The subpanel will not have ground and neutrals bonded (no green screw at the top of the panel and a separate ground bus bar installed (that came with the panel). Because it is a detached building I will install two ground rods attached to the subpanel.

The first question I have is how do I transition between the 1 1/4" conduit and the subpanel. Do I just get one of those fittings for the conduit that has male threads and place it through the appropriately sized knockout in the subpanel? I assume I would need some sort of nut to go on the pvc threads and lock onto the subpanel, but I haven't been able to find one. Is this the correct way to join the subpanel or do I have other choices?

I know that the romex has to be stapled with the proper sized staple near the junction box in the house, the main panel and every 3-4 ft along the way, but what do I use to secure the 4 THWN cables? Is there some sort of pvc fitting that has a cable hold downs like you use with romex? Or is it ok just for it to be wirenuted to the 6-3 romex ( which would be stapled near the junction box) and run loose in the conduit?

I purchased a small PVC box 4" x 4" x 4" which I intended to cut a hole into to glue in the PVC fitting to mate with the 1 1/4" conduit that goes outside. This is where I intend to connect the conductors from the 6-3 romex to the THWN conductors. Does that seem reasonable or is there a better alternative?

Another question I have has to do with the ground rods for the subpanel. I purchased 2 8ft long 1/2 copper coated ground rods. Are these sufficient or do I need 5/8" ground rods? The next question is what size ground wire do I need to run from the ground bus bar on the subpanel through the direct burial acorn clamps on the rods? Can I pull the ground cable out of a section of 10-3 romex and use that to connect the rods or do I need thicker cable? Also, do you just literally drill a tiny hole in the side of the garage to put the wire through or do I need to protect it with a little section of conduit?

Thanks,

Christopher


Last edited by Chris Dopp; 06-26-2009 at 02:55 PM. Reason: fix typo
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Old 06-26-2009, 02:48 PM   #2
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A few slightly different questions on subpanel wiring.


To transition from the pvc to the panel, you would use a Terminal adapter and a lock nut.
Since you are using 1 1/4 inch, you would need a 1 1/4 ta and a 1 1/4 lock nut.

How are you getting the pvc out of the basement? What I do is run a short pvc from the box to an lb on the outside and then down into the trench.
The thwn must be in conduit from box to box.
The box must have a min of 35 cubic inches to hold the wire you have. the size should be imprinted into the box.

It is ok for the wire to just be wire nutted to each other and not have to clamp the thwn.

Go with a #6 or #4 bare cooper and run from acorn clamp to acorn clamp to the panel.
A small hole in the floor or wall is all that is needed.

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Old 06-26-2009, 03:13 PM   #3
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A few slightly different questions on subpanel wiring.


Thanks for the info. is the 1 1/4 lock nut you mention made of pvc plastic or is it metal?

I was planning on doing what you said, glue on a small section of pvc through the wall to a LB fitting.
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Old 06-26-2009, 03:18 PM   #4
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A few slightly different questions on subpanel wiring.


Metal is best, Depo or Lowes has them.
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Old 06-26-2009, 03:20 PM   #5
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A few slightly different questions on subpanel wiring.


Quote:
how do I transition between the 1 1/4" conduit and the subpanel.
male adapter (sometimes called fitting or terminal adapter) and locknut.


Quote:
do I have other choices?
Yes but the MA is the logical choice.


Quote:
what do I use to secure the 4 THWN cables?
The thwn wires (not cables) dont need to be secured in the jbox.





Quote:
I purchased a small PVC box 4" x 4" x 4"
Use a bigger box and make it easy on yourself. The wires will fold into a 6x6x4 much easier/cleaner.

Quote:
Are these sufficient or do I need 5/8" ground rods? The next question is what size ground wire do I need
1/2' rods are good. Run any kind of #6 wire minimum (I think it's #4 if "subject to damage" whatever that means.


Quote:
do you just literally drill a tiny hole in the side of the garage to put the wire through or do I need to protect it with a little section of conduit?
A smal hole is fine. If you want to use conduit, use PVC
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Old 06-26-2009, 03:55 PM   #6
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A few slightly different questions on subpanel wiring.


What are you using for your building disconnect requirement?
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Old 06-26-2009, 07:53 PM   #7
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A few slightly different questions on subpanel wiring.


Hmm... I overlooked that. I guess the simplest thing to do would be to switch from a main lugs panel to get a panel with a 100 amp breaker? It would be fed from the 60amp breaker in the main panel. Would that meet the requirement? What other options do I have? A fuseable disconnect?
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Old 06-26-2009, 08:24 PM   #8
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A few slightly different questions on subpanel wiring.


Quote:
Originally Posted by Chris Dopp View Post
Hmm... I overlooked that. I guess the simplest thing to do would be to switch from a main lugs panel to get a panel with a 100 amp breaker? It would be fed from the 60amp breaker in the main panel. Would that meet the requirement? What other options do I have? A fuseable disconnect?
Yes it would meet the requirement. You can also buy a mainlugs panel that utilizes a double pole breaker installed on the busses and you backfeed it with hots from the feeder coming from the main panel. You must install the hold down kit on the breaker to make it compliant. Like the below square d Homeline panel......

Also a good way to go is a square d Qo200TR rain proof disconnect switch. It is service rated as long as the ocpd ahead of it is 60 amps or less. You land your feeder hots on the disconnect, pass the neutral through and connect your ground to the ground bar. Then go on to your main lugs panel. The disconnect needs to be mounted very close to the entry point of the feeder either outside or inside to pass code. It is simply a 60 amp QO breaker case without overcurrent abiltiy. Makes for a nice disconnect since it is service rated. It primarily is used for an airconditioning disconnect but will pass for your building disconnect if used as specified for service rating. They are commonly found at the big box stores. Very affordable..less than 20 bucks.
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Old 06-26-2009, 09:45 PM   #9
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A few slightly different questions on subpanel wiring.


Quote:
I know that the romex has to be stapled with the proper sized staple near the junction box in the house, the main panel and every 3-4 ft along the way, but what do I use to secure the 4 THWN cables? Is there some sort of pvc fitting that has a cable hold downs like you use with romex? Or is it ok just for it to be wirenuted to the 6-3 romex ( which would be stapled near the junction box) and run loose in the conduit?
You don't need to secure the thwn. I would not use wire nuts I would use distrubution blocks mounted in the jb. You can get snap on protective covers if you like.


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