Bonding a residential shed with sub-panel.

Status
Not open for further replies.
M

Mgarf33

Member
Location
Virginia Beach, Va
I'm a bit confused about bonding a wooden shed utilizing a sub-panel. 250.32A which states: "Buildings or structures supplied by feeders or branch circuits shall have a grounding electrode or grounding system..."

This is a large wooden structure located ~25' from the main panel in the residential home. The main service entrance panel has the standard 2 grounding electrodes, and is feeding a sub-panel in the shed. The shed does not have any metal plumbing or other metal structural components. The sub-panel will serve single phase cord and plug type equipment, and a mini-split heat pump unit. The shed's sub-panel will have 3 conductors w/ additional ecg.

There is an exception to 250.32A, "a grounding electrode shall not be required where only a "single" branch circuit, including a multi-wire branch circuit, supplies the building or structure, and the branch circuit includes an equipment grounding conductor..."

Now, would you:

1. install a separate grounding electrode for the shed?
2. run a bonding wire outside the underground conduit from the main panel's existing rod to the new sub-panel?
3. not worry about the bonding this structure because there is not metal in the structure other than the sub-panel itself or because of the exception? I don't think this exception applies because this structure will have several circuits.

Thanks.
 
NEC requires a grounding electrode system for any building served by a feeder, but it 40 amp or 4000. this is protection from lightning.
A feeder is a circuit that feeds a panel, some call it a "subpanel" but thats not a code term.
Please look up the definition of a branch circuit..
The exception for a single or MW branch circuit is probably due to the limited abount of equipment that would be damaged by lightning.
So just install 2 ground rods and be done with it.
 
The shed requires an EGC run with its supplying wires in any case. That those wires are supplying a panel makes it a feeder. That the panel is in a separate structure requires an electrode. The exception refers to existing 3-wire feeders; you should run 4 wires.

So, the answers to your questions are:

1. Yes.
2. No.
3. Do not "bond" the neutral to the EGC/GEC in the shed's panel.
 
Of course, yes I'm dealing with a feeder, not a branch circuit, so the exception would not apply.
It looks like a couple grounding electrodes are going to be needed.


Yes, I know that neutral to case bonding on the shed panel is not permitted, to help eliminate the parallel paths back to the source.

My whole concern with this, wouldn't this now eliminate the "zero potential" that the main house is supposed to be?

It swear I watched a Mike Holt video on this a few years ago, about how excessive grounding electrodes cause more problems than good.


Thank you for the replies.
 
Yes, you could have potential between the neutral and the egc due to voltage drop, but should still have no potential between the house and building grounding electrodes because they normally do not carry current until there’s a fault. If the opposite was true, bonding swimming pools would be counterproductive.
 
Mgarf33 said:
My whole concern with this, wouldn't this now eliminate the "zero potential" that the main house is supposed to be?
Click to expand...
That's more of a concern on the EGC than the neutral.

Plus, the feeder EGC will effectively tie together the house and shed electrodes, at least to the extent that the feeder requires it.
 
Status
Not open for further replies.
Top