Question about sub panel ground

99% of homes are a 3 wire service. The power company does not give you a ground. You create the ground when you install the service, this is done by takeing a wire to the street side of the water meter or to ground rods installed outside.


I beleive in the US you used to be able to run a 3 wire to an outbuilding and create your ground with a ground rod at the subpanel. If this is an old install and there is a ground rod at the subpanel, then it probably is a legal install and they have no ground to fight you on it.

Someone with more knoweledge of the NEC will let you know more details on this rule.

In Canada I beleive you would need a 4 wire service.

unless a 4 wire feed to the outbuilding was required when it was installed, tell the home inspector (who is likely not a licensed electrician or even a truly qualified electrical inspector) to take a hike. If it was installed when 3 wire was legal, it is grandfathered.

unless something has since been changed that would make the install illegal.

the one situation I can think of is when 3 wire was legal, there could be no other electrically conductive pathways between the house and the outbuilding. If there is such a path, a 3 wire would not be legal even when 3 wire feeds were legal.

I understand that a separate ground can be run but the 3rd wire already serves as ground so isn't that redundant?

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No, it isn't. A ground and a neutral are different and provide different benefits.

While your existing 3 wire sub-panel may well be code compliant under the NEC when it was installed, if the buyer wants to play hardball he can make you bring it up to current code or negotiate a price to do so. Your choice may be to comply or lose the sale.

I would tell your real estate agent that the home inspector is quashing the sale and that the installation is code compliant based on the year it was installed. Agents can place pressure on the home inspector to "recognize the error of his ways". I am not suggesting that the inspector overlook a legitimate issue but he should research the code in affect at the time of the install.

BUT it is a tough sellers market, it might be cheaper to comply than to fight.

The OP states the workshop is off the back of the attached garage. This may not have ever been legit.

Jim Port said:

The OP states the workshop is off the back of the attached garage. This may not have ever been legit.

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please explain why you believe so.

I am envisioning a house with an attached garage and the workshop is attached to the garage, ie this is not a detached structure and would not be eliglble for the 3 wire feeder exception.

Jim Port said:

I am envisioning a house with an attached garage and the workshop is attached to the garage, ie this is not a detached structure and would not be eliglble for the 3 wire feeder exception.

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You might be right. As I re-read the original post, I can see where you can have that interpretation. I read it that it was not connected but I could.....


I could be.......


I just can't say it Jim. I may not be right sometimes but I just cannot admit to being wrong.:laughing:

so, we need some clarification. Is this workshop physically connected to the garage which is physically connected to the house?

If the shop and the garage are attached, Jim would be correct and it would require a 4 wire feeder.

That's right, the garage is attached to the house and the shop is attached to the garage.

Sounds like I will need to look into a grounding rod.

Thanks for your help.

Richo said:

That's right, the garage is attached to the house and the shop is attached to the garage.

Sounds like I will need to look into a grounding rod.

Thanks for your help.

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A ground rod is for high voltage events like lightning. It has nothing to do with properly grounding a subpanel in an attached structure.

You need a 4 wire feeder to the subpanel.

So how do you get a 4 wire feed to the panel when the main panel in the house has a 3 wire feed?

At the service is the only place were it is allowed to bond the neutral to ground. Bonding other locations can lead to objectionable current where it should not be. You do not want current flowing on parts that should not carry voltage.

driving a rod will not solve this problem. It was improperly installed to start with.
Inside a dwelling all feeders must be 4 wire. your service is 3 wire (all of them are) the fourth wire is actually "created" inside the main panel and must be shared to all sub panels(in attached buildings).


You therefore must add a conductor to your feeds. this conductor must be either in the same cable or conduit. it can not be run along side.

Richo said:

So how do you get a 4 wire feed to the panel when the main panel in the house has a 3 wire feed?

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you just take 4 wires to the subpanel from the main panel. In the main panel, the ground and the neutral will be connected to the same effective point. In the subpanel, the ground and neutral will be separated. The ground will be bonded to all metal within the system while the neutral will be bonded to only the neutral bar in the panel.

there is one saviour here if it was installed in metal conduit. Was it installed in metal conduit?

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Buyers will often present an offer with a lot of "subject to clauses." Example: "This agreement is subject to seller's updating the subpanel feed to 4 wires."

The seller is not obligated to accept all or any of those conditions.

Furthermore you can write up the sales contract so that you are never obligated to fix anything, leaving the buyer just with the option of backing out.

The seller can refuse to fix the issue and the buyer can refuse to close the sale. But if the seller is motivated to sell the best course of action may be to have it rewired. And since the sub-panel apparently never was to code, the question of permits and inspection might arise.

And since now the seller is aware of the issue, he will have to disclose it to any future prospective buyers. Most states have disclosure forms where the seller has to tell any known problems to a buyer.

Unfortunately it wasn't installed in metal conduit, just pulled through the walls.

you just take 4 wires to the subpanel from the main panel. In the main panel, the ground and the neutral will be connected to the same effective point. In the subpanel, the ground and neutral will be separated. The ground will be bonded to all metal within the system while the neutral will be bonded to only the neutral bar in the panel.

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It's only about a 15 foot run and a matter of pulling some paneling off the walls in the garage to take it out and replace it, so this sounds like it shouldn't be more than a couple hours work to do it the right way.

Thanks guys!