Grounding requirements for main panel and subpanel

Question

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.

Answer 1

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.

Answer 2

There's National Code, State Code and Local Code. All vary based upon the panel's opinion, but as long as the wiring safely gets the job done, then that's all that counts.

1. Main Panel has two hot wires and a neutral wire supplied from the meter. Electrician adds a ground wire, which is connected to a grounding source, such as a ground rod. The ground wire is to be connected to the ground bar, the neutral bar and the case of the service panel. Electrician is also to wire in a second ground source, in case the main ground line gets cut. The second source can be metal water line, metal conduit, metal well head, etc.

2. Sub Panel requires the same configuration as Main Panel, with the exception of one thing: in a sub-panel the neutral bar is NOT grounded; it is to be attached to the sub-panel case with spacers to prevent grounding.

Notes:

• If there is no second ground source available for the sub-panel, then a ground wire may be run from the Main Panel to the Sub Panel and used as a second source of grounding.

• If the Sub Panel is in the same building as the Main Panel, then a grounding rod isn't required. A ground wire from the Main Panel to the Sub Panel may be used instead

(This information is based on the 2020 National Electrical Code Book.)

Answer 3

The NEC only requires two ground rods if one doesn't meet the 25ohms requirement. If an additional ground is installed then a minimum 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.

Answer 4

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.

Answer 5

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.

Answer 6

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 calculation 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.

Answer 7

A lot of these guys r either half right or all wrong. Going from 60 to 200 greatly increases what u can add down the line assuming ur main is not loaded to high. The conduit is technically grounding ur sub panel but it's not copper and not up to code. Ur ground has to provide the easiest path for electricity and stainless steal or galvanized pipe is not even close to copper which is what most of ur wiring is. And ur water line needs to be bonded but it's not suitable for ur main ground. That's how u get electrocuted in the shower. U need to run a ground wire to ur sub. My boss says a 2nd rod is now code. It has to be 8ft long and 6 ft from the 1st. Easy peasy to do both things. Ur sub panel has insulation to keep the neutral and ground separate. Combine them and u will surely trip the main. Ur main DOES have a disconnect. It's the 200 amp breaker. When u flip it, the whole thing loses power. Ur sub may not since it has a breaker in ur main to serve as a disconnect. Disconnects r any device that immediately turns off power.