Hello all,
Just mounted my 70 amp subpanel on my garage wall. My question is: Do Subpanels need to be grounded with their own separate ground rod. I remember someone saying that a 100 amp or above does but not if less then that. Obviously the panel will be grounded through the feeder cable.
Whoever told you that was wrong. Amperage of the panel does not change the ground requirements. Is your garage attached? If yes, then you do not need to add ground rods. Run a 4-cable feeder to the sub from the main and pull ground through that. Make sure that ground and neutral are not bonded in the sub. Remove the bonding strap from the neutral bar. If your garage is not attached, then you need to add ground rods.
Thanks J.A.
The garage is detached so I will install the ground rod tomorrow with #6 copper. I already bought 10/3 UF and am going to start trenching and running 1" conduit in the morning. I understand the neutral bus bar issue but never was able to understand why the bonding screw is to be removed. If neutral and ground are bonded at the main panel why is it bad to bond them at the sub? Don't worry...I will separate them but am just curious.
Rod
If they are bonded together at the subpanel then the neutral current will be split evenly between the neutral and the equipment grounding conductor between the subpanel and the main panel. The equipment grounding conductor is not suppossed to carry current under normal conditions.
Since you are using 10/3 UF are you going to be putting a 30 amp main breaker in your 70 amp subpanel?
Cheers, Wayne
Good catch. I was focused on the grounding question. 10/3 would make a pretty useless subpanel.
Why? It runs all my power tools with no problem at all, including a tablesaw and dust collector together. Sure, bigger is better, but when I ran mine there were other considerations that made 10/3 an easy choice at the time.
I agree with Edwin.
All I ran to my detached garage was 10/3 wg, used a 60 amp, 4 circuit subpanel and a 30 amp breaker in the main box.
That would handle anything I wanted to use since I don't weld.
How many tools can one guy use at one time???
I dunno. When I ran a subpanel in my attached garage, I ran it as a full
100A sub, with #4 AWG, the works. I figured I'd just overdo it from the start so I would not have to redo it later. However, I agree with you. 10/3 wire in a garage sub would be more than enough garage power for most folks.
It couldn't have been "full 100a" with 4 ga wire, you really need 2. You use 310.16 to size this feeder, not 310.15(B)(6)
The inspector didn't have a problem with it.
He missed a violation, it happens. Perhaps he just decided you will never use the 85a the #4 is good for but it still is not really legal. A lot of people mis-apply 310.15(B)(6). It is onlky for the main feeder or service conductors to the whole dwelling. That assumes the load diversity you have in a home.,
#4cu THHN 90C is 95A not 85
The problem with that idea is the breaker lugs are only rated at 75c.
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