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-   -   Grounding garage sub-panel (http://www.diychatroom.com/f18/grounding-garage-sub-panel-157690/)

tristanlee85 09-23-2012 09:40 AM

Grounding garage sub-panel
 
Hi all -

I am working on re-wiring my garage and have been given some advice from a friend who is a licensed electrician, but I just wanted to clarify a few things since he isn't always available to answer my questions.

What I am planning on doing is running 60A service out to the garage to a sub-panel. I am going under ground for about 15ft in 3/4" PVC. On my main panel, I have installed a 60A breaker and so far I have ran 8ga THHN (hots and neutral) to the garage - nothing is currently hooked up.

One thing I am uncertain of it whether I would have a grounding rod specifically for the garage, or if I can run my ground through the conduit as well and ground at the main panel.

Also, I have been reading on isolating the neutral in the sub-panel and I believe this is done by removing the screw that connects the neutral bar to the panel itself. Is this also required?

The sub-panel will have 5 breakers in it (4 110V and 1 220V). I believe with 6 requires a main cut-off to the panel, which I am assuming my 60A breaker in the main is a sufficient cut-off for the sub-panel.

I have read a mixed amount of things regarding the ground and neutral scenario so I am looking to confirm what I have been told by my friend with what you all are able to provide. Thanks in advance!

k_buz 09-23-2012 09:46 AM

Quote:

Originally Posted by tristanlee85 (Post 1015597)
Hi all -

I am working on re-wiring my garage and have been given some advice from a friend who is a licensed electrician, but I just wanted to clarify a few things since he isn't always available to answer my questions.

What I am planning on doing is running 60A service out to the garage to a sub-panel. I am going under ground for about 15ft in 3/4" PVC. On my main panel, I have installed a 60A breaker and so far I have ran 8ga THHN (hots and neutral) to the garage - nothing is currently hooked up.

One thing I am uncertain of it whether I would have a grounding rod specifically for the garage, or if I can run my ground through the conduit as well and ground at the main panel.

You need both. An equipment ground from the main panel and 2 ground rods at the detached structure.

Also, I have been reading on isolating the neutral in the sub-panel and I believe this is done by removing the screw that connects the neutral bar to the panel itself. Is this also required?

Yes

The sub-panel will have 5 breakers in it (4 110V and 1 220V). I believe with 6 requires a main cut-off to the panel, which I am assuming my 60A breaker in the main is a sufficient cut-off for the sub-panel.

You assume wrong. You must have a single disconnect at the garage. If you have a main lug panel (in the garage) and have the space, you can install a 2P 60A breaker. The breaker in the house will not suffice.

I have read a mixed amount of things regarding the ground and neutral scenario so I am looking to confirm what I have been told by my friend with what you all are able to provide. Thanks in advance!

answers in red

tristanlee85 09-23-2012 09:46 AM

To explain my knowledge on the grounding question, I have been told/read that since the sub-panel is in a different building, I need 2 grounding rods at least 6ft apart + I need to run a ground back to the main panel. However, the garage is attached to the house with the separation of a breezeway, but still technically connected so I am not sure if that changes anything based on NEC requirements (which I am not familiar with).

tristanlee85 09-23-2012 09:47 AM

Great, thanks for the reply. I ended up posting a follow-up to my grounding questions exactly how you answered it, so that's good to know. Definitely appreciate the response!

k_buz 09-23-2012 09:51 AM

Quote:

Originally Posted by tristanlee85 (Post 1015603)
To explain my knowledge on the grounding question, I have been told/read that since the sub-panel is in a different building, I need 2 grounding rods at least 6ft apart + I need to run a ground back to the main panel. However, the garage is attached to the house with the separation of a breezeway, but still technically connected so I am not sure if that changes anything based on NEC requirements (which I am not familiar with).

I THINK the garage would still be considered detached. I haven't run into this before. Just to clarify something, the new ground rods would only be required if the garage was considered to be a detached structure, but you would still need the equipment ground in the PVC. The ground rods should be connected to to the subpanel's ground bar. If the panel did not come with one, you must purchase one separately.

tristanlee85 09-23-2012 10:44 AM

Here is what I am working with:

http://i88.photobucket.com/albums/k1...ps8331f070.jpg

On the left, you can see the service line and grounding rod from the house and then my conduit from the house over to the garage. If I add in 2 more ground rods near the conduit box of the garage, seems like that would be a lot of rods in a close area of each other, and I'm not sure if rods that close together would be an overkill or code requirement.

J. V. 09-23-2012 11:22 AM

I can't see anything in your picture. It is way to small, and it is side ways. If the garage is physically attached to the house it is not detached. The roof would be the key in your case. Same roof, its not detached. Sometimes breezeways do not actually attach to either structure and in that case the garage is considered detached.
It sounds like you did not pull a ground wire (EGC) in the conduit. You need it. 2 hots, 1 Neutral and one ground. This is regardless of detached or not.
The rods are required if the garage is detached. If its not detached, then you don't need the rods. If you need them you need two located as close to the garage sub panel as possible. Pound them in 6' apart and connect them to the garage sub panel.

jrclen 09-23-2012 12:16 PM

You will also need wet location conductors. THHN is not rated for use in buried conduit. THWN is. Maybe yours are dual rated, take a look on the wire.

With a 4 wire feeder to a detached structure in my state and many others only one ground rod is required.

tristanlee85 09-23-2012 12:59 PM

Quote:

Originally Posted by J. V. (Post 1015658)
I can't see anything in your picture. It is way to small, and it is side ways. If the garage is physically attached to the house it is not detached. The roof would be the key in your case. Same roof, its not detached. Sometimes breezeways do not actually attach to either structure and in that case the garage is considered detached.
It sounds like you did not pull a ground wire (EGC) in the conduit. You need it. 2 hots, 1 Neutral and one ground. This is regardless of detached or not.
The rods are required if the garage is detached. If its not detached, then you don't need the rods. If you need them you need two located as close to the garage sub panel as possible. Pound them in 6' apart and connect them to the garage sub panel.

The picture is clickable and will expand larger. It's quite large and detailed even at the slight angle. Here's a direct link: http://i88.photobucket.com/albums/k1...g?t=1348411168

I did not run the ground cable in the conduit yet because I wasn't 100% sure. I just purchased some thing morning and will be running it. Everything is under 1 roof so it won't be considered detached. However, I did pick up a single ground rod and will be pounding it in outside the garage where the wire comes in. It'll be about 15ft from the existing ground rod and may not be needed, but I'll add it in anyway.

Quote:

Originally Posted by jrclen (Post 1015680)
You will also need wet location conductors. THHN is not rated for use in buried conduit. THWN is. Maybe yours are dual rated, take a look on the wire.

With a 4 wire feeder to a detached structure in my state and many others only one ground rod is required.

I was incorrect on the conductor. It's THWN-2 which is good for wet/dry conditions not exceeding 90*C. As mentioned above, it's not considered detached, but I will be using a 2nd grounding rod just because.

jrclen 09-23-2012 02:48 PM

Sounds good. One further glitch, your #8 THWN is good for 50 amps max.

tristanlee85 09-23-2012 03:26 PM

Yeh, I just realized that -ugh! My licensed friend who was the one telling me which wire to get for our proposed 60A panel said #8 would be fine, so I got it. Looks like I should have looked at the spec sheet myself before wasting $$. Should have got #6... Seeing as how so far I've been just fine living on a 15A fuse in the garage for 5+ years, 50A will probably still do for my intentions... The previous owner of the house just buried 12/3 with no conduit so it was a pain to cut of the patio to lay PVC, but at least now if I do need to upgrade, it's just a matter of snaking new wire.

J. V. 09-24-2012 11:40 AM

Sorry about the picture. Still I got nothing from it. Like you said, 50 amp is fine and then you can use the same wire. Take the ground rod back. You don't need it.


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