PDA

View Full Version : subpanel ground rod location and installation



leejosepho
10-21-2007, 04:02 AM
I plan to install a subpanel for my garage and new workshop, and I understand the bonding issue and that it must have its own ground rod. The new panel will be located about 12' in from an exterior wall.

Am I correct in thinking the ground rod must be either right next to an outside wall or actually outside?

Speedy Petey
10-21-2007, 04:32 AM
The ground rod can be on the other side of the building as far as code is concerned.

Is the panel going to be 12' inside the building? If so then you need a disconnect outside or just inside the structure. Same as with a main service.


I assume this is a detached building?

leejosepho
10-21-2007, 06:01 PM
The ground rod can be on the other side of the building as far as code is concerned.

Okay, but can it go down through the slab floor *inside* the building or does it have to be outside?


Is the panel going to be 12' inside the building?
...
I assume this is a detached building?

No, our garage is attached to the house and the new workshop is behind the garage. Depending upon the actual location to be selected, the panel could be as close as 6' from an outside wall. My overall assumption here is that the ground rod has to be outside the structure altogether, but I would put it down through the floor (How far from outside?) if that is acceptable.

480sparky
10-21-2007, 06:09 PM
No, our garage is attached to the house and the new workshop is behind the garage.

Are you saying the garage is attached and the workshop isn't?

Speedy Petey
10-21-2007, 06:14 PM
Yeah, hold on! Is the garage attached and the shop not, or are both attached???

If the panel will be in the garage, or both are attached, then NO ground rod is required, needed or wanted. Same with the disconnect/main breaker.


MORE details please. :confused:

leejosepho
10-21-2007, 06:24 PM
Please pardon the confusion.

The garage is attached at the East side of the house, and the new workshop is attached to the North wall of the garage and it also overlaps the house by four feet. Our main panel is in the basement at the opposite corner of the house, and there are presently no circuits going to either the garage or the workshop.

Speedy Petey
10-21-2007, 06:25 PM
Then NO ground rods are needed or wanted for this sub-panel, and you can install a main lug panel anywhere you want.

Speedy Petey
10-21-2007, 06:27 PM
http://www.terrylove.com/forums/image.php?u=9362&dateline=1178056435Hey Lee, is this what you look like after you shave? :D

leejosepho
10-21-2007, 06:39 PM
Nope. The real me only has 10 teeth ...

leejosepho
10-21-2007, 06:47 PM
Then NO ground rods are needed or wanted for this sub-panel, and you can install a main lug panel anywhere you want.

Okay, so what about bonding? When I put a panel in a detached garage at another place several years ago, I was told to not bond it and to install a ground rod ... and I had been assuming I would have to do the same here.

Speedy Petey
10-21-2007, 06:56 PM
You then had a detached structure fed by a three wire feeder.

You now have an attached structure sub-panel and MUST run a "4-wire" feeder.
In the sub-panel the neutral bar is NOT bonded to the panel box and you must add an additional ground bar.
The neutrals are ground must remain isolated.

leejosepho
10-21-2007, 07:01 PM
Okay, thank you!

leejosepho
10-23-2007, 03:32 AM
You now have an attached structure sub-panel and MUST run a "4-wire" feeder.
In the sub-panel the neutral bar is NOT bonded to the panel box and you must add an additional ground bar.
The neutrals are ground must remain isolated.

I have been searching other discussions here, and it looks like all four wires must be at least the same minimum size unless the subpanel is for a "balanced load" like a 240-volt dryer or water heater. Correct?

Speedy Petey
10-23-2007, 03:50 AM
No. The neutral can be downsized since this will be a 120/240v panel and at least some, if not much of the panel's load will be balanced.
This is determined by the load calculation, but a general rule of thumb is two wire sizes smaller. NEC 220.61 is the code reference.

The ground is sized according to NEC Table 250.122

Speedy Petey
10-23-2007, 03:52 AM
......unless the subpanel is for a "balanced load" like a 240-volt dryer or water heater.A dryer is NOT a balanced load. There are several 120v loads in a dryer. They are 120/240v as opposed to a water heater which IS a straight 240v load.

leejosepho
10-23-2007, 05:29 PM
Overall then, and I am probably not going to like the answer here, I will have to run conduit? Coming off a 60-amp breaker, I will be going just a little under 50' to the subpanel, and I am assuming I cannot run a bare ground wire between floor joists and through walls alongside a 3-strand "Romex" of the proper size ...

jwelectric
10-23-2007, 05:37 PM
300.3(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).

Speedy Petey
10-23-2007, 07:22 PM
Define "3 strand romex". Do you mean "3-wire"? As in black, red, white, ground? :confused:

If it is 3-wire then the ground will be the proper size automatically.
If it is 2-wire then it was never correct in the first place.

Now I'm confused....

leejosepho
10-24-2007, 03:03 AM
Define "3 strand romex". Do you mean "3-wire"? As in black, red, white, ground? :confused:

If it is 3-wire then the ground will be the proper size automatically.
If it is 2-wire then it was never correct in the first place.

Now I'm confused....

I have in the past worked with 4-wire SJ cord wiring 3-phase motors and such, but I do not recall ever seeing 4-wire "romex". So, I was mistakingly thinking about black-white-ground 3-wire cable while assuming I would have to add a ground wire to get a total of four ... and I now realize all of that would incorrectly add up to 2 hots and two grounds.

Speedy Petey
10-24-2007, 04:00 AM
and I now realize all of that would incorrectly add up to 2 hots and two grounds.Exaaaaactly.
You need ... hot, hot, neutral, ground ...in the same cable or raceway.

ked
11-05-2007, 10:38 AM
NM cable for example, 6-3wG, or 4-3wG is four wire cable.