Separating Grounds & Neutrals in Subpanels

Kyle_in_rure

Hello,
New to the website here. I have a question about subpanels; I understand that they are supposed to have a separate four wire feed, and are not supposed to have the neutral and ground bars bonded. My question is, I have seen a few instances where 3 wires (hot+hot+neutral...no ground) were ran to a detached structure, and a ground rod was driven at this separate structure. In the panels the neutral and ground bars were bonded together. What exactly is dangerous about this situation?

Thanks.

MCB

Those are fine in a detached structure with a separate ground - either a rod or plate in the ground.

Cannot do that with a panel that is bonded from the main service.

k_buz

That is not true in the US.

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Kyle_in_rure

What exactly do you mean? If four wires (hot+hot+neutral+ground) were run to the structure, they could not be bonded in the sub because the ground could carry current. Is that what you mean?

Or does this mean that any instance where neutral and ground are bonded in the main panel, there can never be a bond in a sub panel?

Thanks again.

MCB

I had the understanding the CEC was getting closer to the NEC with the changes in 2012....

We can either ground a separate building using a feeder from the main with a separate ground plate or rod OR run the ground from the main service without a separate plate or rod. As long as all the grounding procedures are followed.

MCB

If you run a bonding wire(ground) to the different structure, you cannot ground the neutral at the subpanel.

k_buz

The ground rod does not act as an equipment grounding conductor. The ground rods are for lightening protection. This is why a separate equipment grounding conductor is require for a subpanel. Keep in mind that if the feed to the detached subpanel is in continuous metal conduit (EMT/Rigid), the conduit can act as the equipment grounding conductor. In this case, only three wires would be running to the sub.

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Kyle_in_rure

So, there are a couple of structures on my property (a barn & workshop) that have subpanels from the main back at the house; no grounding conductors were run from the main to these subs (only 2 hots and a neutral), and they are not in EMT, grounding rods were driven and neutrals/grounds are bonded at these subpanels. Is there any risk of shock or other fault problems?

diystephen

In a detached building we are required to run H-H-N-G and utilize a ground rod (I believe it's now two rods.)

MCB

We've generally gone from the two ground rods 2m apart to a plate. Too hard to get the rods deep enough to meet the requirements in our province, anyway. But you ALSO bring a ground from the main?

MCB

As long as the grounding rods are deep enough to satisfy your local authority for grounding rods/plates/etc, and your boxes are bonded properly, sounds good to me. You are just needing to get a potential fault current to the earth around your structure and bring it up to the same potential without hurting anyone.

Kyle_in_rure

Alright, Thanks again for all the answers.

Missouri Bound

Kyle...where are you located? It's obvious that there are some differences in code between the US and Canada and it would suit you well to disregard information form the one which doesn't apply. It's a matter of what is right and wrong, rather than differing opinions. In the states, unless you are doing an electrical remodel you do not have to change existing wiring.

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Kyle_in_rure

Located in the states, my main concern was with safety, i.e. I don't want the metal frames of appliances shocking me when I use them.

brric

Your installations may have been code compliant when they were installed.