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-   -   Ground rod or not? (http://www.diychatroom.com/f18/ground-rod-not-23445/)

brotherman 07-09-2008 11:07 PM

Ground rod or not?
 
I have a detached building that I am going to use as a woodshop. I am installing a 100amp subpanel in the building. The building is only about 15 feet from the main panel that supplies my home, which is where the feeder breaker will be. Do I install a new ground rod for this subpanel, or do I ground back to the main service panel?

Thanks,
Chad

jimmy21 07-09-2008 11:14 PM

install ground rods and keep the nuetral and ground bonded together other on the subpanel




.......corrected

brotherman 07-09-2008 11:30 PM

seperate neutral and ground from one another? Neutral wire to neutral bar, and ground wire coming from ground rod to equipment ground in subpanel?

talking about electrical work, I probably sound ignorant, so please excuse

Thanks,
chad

jimmy21 07-09-2008 11:34 PM

err wait, i screwed up on that, i was typing without even thinking. You want them together. There will be two seperate bars, and on the subpanel you buy there will probably be a green screw that you will need to screw in through the nuetral bar tying it to the panel can. Or sometimes there is a bar that you tie the two together. Either way, you need to make sure there is conductivity between the two

Pudge565 07-09-2008 11:37 PM

I thought that you do want them isolated in a sub panel? I may be wrong since it is a detached building but I don't know

BigJimmy 07-09-2008 11:37 PM

Doesn't matter if it's 15ft or 115ft. Separate the ground and neutral busses in the detached power panel, drive a rod and bond to the ground bus, and run a ground wire to the source panel. The important thing here is that, unlike your service panel, the ground and neutral busses must be separated electrically.

jimmy21 07-10-2008 12:30 AM

Quote:

Originally Posted by Pudge565 (Post 137705)
I thought that you do want them isolated in a sub panel? I may be wrong since it is a detached building but I don't know

if its in the same building you would. in a separate building you want to drive ground rods and separate the ground and neutral

Pudge565 07-10-2008 12:40 AM

Quote:

Originally Posted by jimmy21 (Post 137703)
err wait, i screwed up on that, i was typing without even thinking. You want them together. There will be two seperate bars, and on the subpanel you buy there will probably be a green screw that you will need to screw in through the nuetral bar tying it to the panel can. Or sometimes there is a bar that you tie the two together. Either way, you need to make sure there is conductivity between the two

Ok this is why I asked cuz in this post your telling them to keep them bonded.

Stubbie 07-10-2008 02:25 AM

2 Attachment(s)
Depends on what code cycle your inspector is using. Prior to the 2008... 120/240 volt feeders to detached buildings could be 3 wire H-H-N.....unless another metallic or conductive path existed (metal water pipe, data com cables etc..) then you are required to run a 4 wire feeder H-H-N-Grd. If your inspector is using 2008 then 4 wires are required as the 3 wire feeder is no longer allowed.

Prior to 2008 NEC Cycle (no metallic path other than feeder) 1st image....2nd image is 2008 ( I made the drawing in 2004 as a 4 wire feeder BUT is now required in 2008)

BillyD 07-10-2008 07:10 AM

In your 3 wire feeder you show the Neutral and ground bonded. Everything we read says the neutral has to be isolated in a sub panel.

HouseHelper 07-10-2008 08:50 AM

Quote:

Originally Posted by BillyD (Post 137765)
In your 3 wire feeder you show the Neutral and ground bonded. Everything we read says the neutral has to be isolated in a sub panel.

The three wire feeder functions just like the three wire feeder to your main service. The neutral and ground are bonded, to each other and the enclosure. You need ground rods whether you use three or four wire feeders. As Stubbie pointed out, if 2008 codes are in effect in your area, only four wire feeders are now allowed to detached buildings, with neutral and ground separated.

Pudge565 07-10-2008 10:27 AM

Ok thank you to all of those especially stubbie who clarified this subject for those of us that were a little confused.

BillyD 07-10-2008 11:05 AM

Here is what was posted by the "kctermite" a couple of months back.
[quote=thekctermite;122093]
A sub panel is fed off of the main panel using a double breaker that catches both the A and B phases. The feeder wires are sized based on the size of the breaker in the main panel that serves the sub panel.

In a sub panel, the circuits' neutrals must float...Or be isolated from the grounds. The neutral bar must not be bonded to the panel jacket. This is incredibly important.

J. V. 07-10-2008 11:16 AM

Quote:

Originally Posted by BigJimmy (Post 137706)
Doesn't matter if it's 15ft or 115ft. Separate the ground and neutral busses in the detached power panel, drive a rod and bond to the ground bus, and run a ground wire to the source panel. The important thing here is that, unlike your service panel, the ground and neutral busses must be separated electrically.

This is absolutely correct.
And you must not use the neutral bonding screw either. If it is installed you must remove it.
Neutrals and grounds need to be seperated as BigJimmy said.
Since you are installing this new and have not pulled any conductors, just go with the four wire system. Your local jurisdiction may require this anyway depending on the code cycle they are following. Re: Stubbie.
You also will need a main breaker for the 100 amp sub panel. You need # 3 conductors (3) and a # 8 (1) ground. PVC conduit would be my choice on this project. You have to dig a trench anyway.
You may also be required to drive 2 ground rods.
Finally, are you getting a permit for this installation? If not, you are making a huge mistake. While permits add to the job cost and inspectors can be *******s, at least you will know that you have a compliant and safe installation.

HouseHelper 07-10-2008 11:21 AM

A true statement by the distinguished mr kctermite. For a subpanel in the same structure as the main panel, it is a requirement that the panel be fed with four wires and that the neutral and ground be isolated. No exceptions.

The difference is for a detached structure. Prior to the 2008 code cycle, you could feed a detached structure with three wires and bond the neutral and ground, as long as there were no other metallic paths between the buildings. That option has now gone away, and not soon enough in my opinion.


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