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viper 08-15-2012 06:31 PM

Grounding of sub we go again..
I have done a few of these over the years and thought I remembered looking this up a couple years ago. I was talking with an estimator the other day that indicated EVERYTHING from the main panel MUST carry ground to it.

The wording I might have missed is that it is still considered a branch feeder?

It was my understanding that a sub panel, per NEC code, was supposed to decouple the bonding strap in a panel to isolate ground and neutral, then carry your neutral/ground from the main panel to the sub as a "neutral only" on one side, then drive a ground rod used as a safety ground on the other side.

IE, loads connected to the sub panel do NOT share the ground and neutral.

What am I missing?

AandPDan 08-15-2012 07:09 PM

Yes, you need to remove the neutral/ground bonding jumper from a subpanel.

You need to run 4 wires to a subpanel. Neutral and Ground are separate, Two hots.

If it’s a detached structure you’ll also need to install two supplementary ground rods tied into the ground bar.

Correct: loads connected to the subpanel DO NOT share the ground and neutral.

viper 08-16-2012 09:00 AM

So there is no instance in which you would not carry the ground conductor from the main panel?

AandPDan 08-16-2012 09:36 AM

You do carry the ground conductor.

4 wires to the subpanel.

2 hots, 1 neutral, and 1 ground.

If a detached structure you ALSO need ground rods in addition to the above.

rjniles 08-16-2012 10:29 AM


Originally Posted by viper (Post 990132)
So there is no instance in which you would not carry the ground conductor from the main panel?

At one time you were allowed to run a 3 wire feeder to a detached structure (2 hots & a neutral) if there were no other metallic paths (water pipes or low voltage cables) between the buildings. Commonly this feeder was triplex run overhead or direct burial. Ground rod(s) were used at the detached structure. This has ben removed from the code but you might find one wired this way.

4 wire feeders are now required.

viper 08-16-2012 01:09 PM

Thanks for that! That all makes sense and I think just a misunderstanding on my part that at some point ground rods and not carrying ground to now carrying ground AND adding a rod, I was misinformed.

I know I have a panel now at my place that uses 2 hots and one neutral/ground, all insulated. The bonding strap is still there too. Certainly works no problem but I think just unbonding it and adding a ground rod should seem to satisfy "some" older code and in this older house, it would probably fly.

Someone just forgot or neglected to drive a rod. Do you have any idea when the code was revised to now include carrying the ground? Just curious how new that is.

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