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I recently had my main service professionally upgraded to 200A and had a 60A subpanel installed in my master suite to support future additions. All work passed city inspection, for whatever that's worth. I'm just now noticing some things about the work that I'm not so sure about.

The main panel is in an separate-attached garage. The majority of circuits enter the house through a covered breezeway between the garage and house. The new 60A subpanel in the master suite is fed by wires in a buried conduit run through the backyard from the garage.

Questions:

Only one ground rod was driven for the 200A panel. Is this sufficient?

There are only 3 conductors between the main and sub. 2 hot and 1 neutral, no separate ground. There is a ground bar installed in the panel, but no wires connect to it. When I asked the electrician about this after the fact, he said that the neutral wire also serves as the ground, and that it is ok to do this in a subpanel. Is he correct? I've read that ground and neutral bars should not be bonded in a subpanel, but in this case there isn't even a ground wire - neutral and ground share the same wire.

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The NEC only requires two ground rods if one doesn't suffice the 25ohms requirement. If an additional ground is installed then a minium of 6' spacing is required between them. The only time the neutrals and grounds are allowed to tie together are in the main disconnect. To keep the neutrals and grounds separated, a 4 wire should have been used to feed your sub panel.

  • There is no outside disconnect. The 200A breaker is on the main panel itself, where the neutrals and grounds are bonded. Sounds like the electrician screwed up by only running 3 wires to the sub. Do you know if a sub can have its own ground rod? Would be much easier than running a 4th wire through the underground conduit. – ErikR May 27 '15 at 22:14
  • It does sound like the electrician screwed you. There's very little price difference in having a 200 amp sub panel instead of a 60 amp subpanel. You are basically paying for the labor. As far as driving a ground rod at a subpanel it is far better to ground to a cold water pipe where it enters the house as long as the pipe is not plastic. But even if you were to do that, it is still illegal to separate the grounds and neutrals in a non main disconnect panel. Basically your sub panel has no ground and is a three wire system. The only way to fix that would be to replace the feeder wire. – Kris May 27 '15 at 22:44
  • Sounds like you are concerned about not having a separated ground at your sub panel, and are wondering if driving a ground rod would make a difference. As I stated above not for separating the neutrals and grounds as only the correct wire would allow that. But maybe, and this is a big maybe, help to deter lightning strikes. Ironically it could possibly attract lightning! – Kris May 27 '15 at 23:50
  • @Kris I don't mean this disrespectfully, but I had to read your comments a couple of times before I was sure you said what I thought you said. ;-) I'm pretty sure I agree with you. – Craig May 30 '15 at 16:43
  • The main panel should be grounded (probably with 2 grounding rods) and the grounded (neutral) and grounding buses should be bonded in the main panel. The subpanel probably isn't far enough away from the main to require its own grounding rod(s), but regardless, it does require a 4 wire feed from the main panel (2 ungrounded conductors, 1 grounded conductor/neutral, one EGC), and the neutral and grounding buses in the panel must be isolated. – Craig May 30 '15 at 16:50
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You might want to read this for some more info but in general, this isn't how it should be. You should have a separate ground run from the main panel to the subpanel.

FWIW I upgraded to 200A from 60A a few years ago, and the electrician only drove a single ground rod. The inspector had me drive another one, I think the requirement was at least 12 ft from the first, and at least 8 ft down, or somewhere along those lines. I'd imagine it might vary by region.

  • Thanks, that was a good read. Sounds like there's a definite safety issue here. I don't expect the electrician to come back to make it right, since it passed inspection (inspector spent <30 seconds looking at the panel with cover on; only cared that circuits were labeled). – ErikR May 27 '15 at 22:23
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Not seeing a line side wire terminated to the ground buss could mean that it’s bonded to the neutral buss with the longer screw that is made to do so,however usually at a sub panel fed with 3 conductors, 2 hot & 1 neutral Requires a separate ground rod driven and terminated to the line side of the ground buss and for the ground not to be bonded to neutral at the sub panel. Code can differ from place to place, if a licensed electrician did the install and it passed inspection, I wouldn’t sweat it.

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Your subpanel required a 4-wire feed, with separate ground wire, unless you have a local ordinance that makes an exception. It's possible the relationship between electrician and inspector has gotten corrupt, and the inspector and electrician have convinced each other that this is OK.

The good news is that ground wires can be retrofitted, as of NEC 2014 (and a bit earlier for some applications).

However, if the conduit is made of metal, that actually is a perfectly allowable grounding path, and that means you are grounded. However that does not explain the lack of ground wires on the ground bar in the subpanel, unless all branch circuits are also in metal conduit. I maintain four buildings, all in metal conduit, and there's not a ground wire in any of them.

You do not need a separate ground rod for this subpanel since it's in the same building. The fact that the route is outside is irrelevant.

You only need 1 ground rod if it passes the magic 25-ohm test. Otherwise you need 2, however they can both be off the main panel. By the way, the reason we require wired ground and ground rods (for outbuildings) is that 25 ohms isn't nearly good enough.

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I am not convinced with all those above. here is the question to know, why you need one grounding or many and the size of the ECC, earth grid, size of the earthing cables based on fault current calculationenter image description here etc, and all this will be based on mathematical calculation and that should be let you know how you get the max. safety. there is another question which type of earthing is suitable for residential bldg. you know there are 4 types (TT, TNS, TN-C Etc) of earthing.

actually grounding needs less than 1 ohm and for lightning protection it should be less than 2 ohm, one grounding may serve the purpose but it is recommend to use 2 (but should be 5m apart), because if 1 cut accidentally, another serves to safe you.

  • Yeah, "general mass of earth" isn't good enough because dirt is not a good conductor, and it can't return enough current to reliably trip a breaker when breakers need to be tripped. If there's a ground fault, the fault would successfully "pull up" the voltage on all parts of your grounding system. Can't have that! – Harper May 4 at 21:34

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