OT: electical sub panel grounding

[Morgans]

OK, here is the deal. I have the original breaker panel fed by a 150 amp line off of a new panel necessitated when an addition was added years ago. The sub panel is fed by a line with three conductors and ground of the correct size.

The inspector at the time ended up getting fired for enforcing code that was not there. With this in mind, he said he wanted a #6 bare ground wire to tie between the original panel and the new panel. That means it would be in parallel to the ground in the service feed cable.

Was he full of it when he told me this? I have been "neating up" the panel along with my renovations for my new basement workshop. The old panel was wired by a left handed chip, or a big bird, it was so messy. I took all but about 5 circuits out and re-organized the whole thing neatly and added a few new circuits for the shop. I feel much better about it, and solved a few mysteries that had always bothered me.

Jim in NC

[Doug Winterburn]

Not sure the extra heavy duty ground hurts anything, but make sure the ground and neutral are not tied together in the sub panel - in other words, separate neutral and ground bus bars and no bonding strap from the neutral bus bar to the sub panel case.

[Mike Marlow]

Just to clarify Jim - what was once the "original" panel is now a sub-panel?

No - it doesn't. The ground only shares one point in common between the two panels so it can't be in parallel. Not so sure about the #6 aspect of what he wanted, but the connection between the two panels (main and sub) is exactly to the NEC spec. If he got fired for that then whoever fired him should be fired themselves. It does not have to be a bare ground - an insulated ground is perfectly acceptable. Bare ground is only specified for grounding stakes.

[clare]

The feed wire was a 3 wire+ground cable The ground was connected to both panels. Adding the #6 bare copper ground between the two panels would, by necessity and the nature of the circuit, mean that the bare ground WAS in parallel with the ground in the feed cable. If the ground in the feed cable meats the requirement of code (which I am 99.999% certain it does) then requiring the extra basre ground was a requirement beyond code, and he needed his knucles rapped good. I suspect this was not his first infraction for requiring "above code"

- hense his firing. Good riddance.

[DJ Delorie]

His point is that there are now TWO grounds between the panels, the insulated one in the cable and a separate bare #6. If both grounds are connected on both ends, there's a loop. Is a loop in a ground allowed?

I didn't get that impression. It sounded like he got fired for enforcing nonexisting rules elsewhere, but the OP didn't say he was fired for *this* case. The OP implied that he now suspects the inspector's requirements *because* he was fired.

So IMHO the case is - the OP is now suspicious, and wants a second opinion. Are bare grounds required? Are ground loops legal?

[Puckdropper]

"Morgans" wrote in news:m13dtr$mv3$ [e-mail]:

I think we're getting confused here. How many pieces of copper are in the feed? 3 or 4?

A second wire, outside the feed, is connected from panel to panel as a ground, right?

Puckdropper

[clare]

You definition is strange. 2 wires, connected to the same thing at each end, put the 2 wires in parallel, and they would share the fault load if power was to short to the panel frame at the "load " end.

It is connected to the main panel ground at the main panel end. So is the bare (or green) wire in the 3 wire+ground cable to the sub panel. It is connected to the ground terminal of the sub panel. So is the bare wire (or green) in the cable from the main panel. That puts the two grounds in parallel. It is also "effectively" in parallel with the white neutral, although not "exactly".

[John McCoy]

"Mike Marlow" wrote in news:m144he$vaf$ [e-mail]:

Yes, it is. If I have a point defined as ground at one end of wire, and I connect the other end of that wire to something, the other end is also ground. If I then take a second wire and connect it to both ends, the second wire is in parallel to the first wire. That is the situation being described.

You have misread the original post. He said he has a four wire cable, and _in addition_ he has another #6 ground wire. The additional ground wire is redundant, but harmless (it might be helpful in the event of a lightning strike, but otherwise it serves no purpose).

John

[John McCoy]

DJ Delorie wrote in news: [e-mail]:

The situation described is topologically a loop, but not electrically.

"ground loop" means something else in the world of electricity.

John

[krw]

Actually, it is. If the two wires are routed separately (if they're run absolutely together, its one wire), there is a loop or a "one-turn transformer", if you will. That's why it's not allowed.

No, it's the same thing for the same reasons (though perhaps different outcomes).

[clare]

4 L1, L2, N and Grnd

A fifth wire, if you want to be accurate., or a second ground.

[clare]

No additional ground rod, and from the OP's initial post, it sure SOUNDED like the external ground conductor went panel to panel. I MAY have mis-interpreted the initial post. If both the cable ground and the external ground went panel to panel, I am correct. If the external ground ran from the service ground ROD to the second panel, you may technically be right.

[krw]

With N and G only tied together in one place, at the entrance panel (which may not be either of the two panels).

[clare]

Which in his case, according to the initial post, IS the main panel (and way back when, USED to be the sub panel - which means the sub panel may or may not be a legally allowed sub-panel. If it had the main braker or fuse in the panel, there is a STRONG possibility the neutral and ground are permanently bonded (does not have a removeable jumper)) Some of those panels CAN ge hacked or modified to separate the neutral from the ground - some can not easily be modified. (and if it is truely "modified" it is no longer an approved electrical device, so again it is not code compliant - so we will ASS U ME this is a compliant insulated(or isolated) neutral panel.

[krw]

The post was confusing. Not sure exactly what he has but the point is still valid. It's possible that none of these panels are the "entrance". They haven't been in either of my last houses.

The separate ground bars are available for many of these boxes. I agree, though, it sounds like they may not be wired so they're separable. They can be rewired (if the parts are available for the boxes).

Hacking, of course, wouldn't be allowed. The boxes and all hardware have to be listed for the purpose. These parts are often available, though.

[Markem]

A ground loop hums at about 60 hz as I recall, not that I ever hooked up one. Well maybe one at a mic input.

Mark

[clare]

Not sure of current panels, but entrance panels (those with the main breaker built in) a few years back often did not have the bonding screw, while panels manufactured without the built-in main breaker (separate - not taking up a "load" slot) most often did have the removeable bonding screw.

[Doug Miller]

"Morgans" wrote in news:m13dtr$mv3$ [e-mail]:

And that's a Code violation AFAIK.

Yes, he was. AFAIK, anyway.

If you want a definitive answer, repost this in alt.home.repair, titled "PING: gfretwell re subpanel grounding". Greg (?) Fretwell is a licensed electrician who is a regular in that group, and whatever advice he gives you, you can take to the bank.

[Morgans]

OK, I will try to be more clear.

I have a three conductor with additional ground conductor cable going between panels. In the main panel, fed from the road, the neutral and grounds are equal, with the normal configuration of the neutral and grounds bonded to the panel frame, and the whole thing grounded to a ground rod and to the neutral coming in from the pole.

In the sub panel, which was the house's original panel, the neutral is not bonded to the frame of the panel, and there is a separate grounding lug connected and bonded to the frame of the panel.

Now for what the cable coming from the main panel is connected to. Remember that it is two hot wires (insulated) a neutral wire (insulated) and grounding wire wrapped as individual strands around all of the insulated conductors, and all of it covered in plastic sheathing. The two hot wires are of course connected to the two breaker busses, the neutral is connected to the insulated buss bar and has all of the neutrals coming from the house circuits connected to it. The buss bar that is bonded to the frame has all of the ground wires from the circuits going to it, and is connected to the ground wire in the service feed cable.

This additional ground wire the inspector wanted was to be a #6 bare copper wire connected at the main panel (service entrance) onto the ground/neutral buss and then run to the sub panel and connected to the ground buss. (which is bonded to the frame)

I believe Clair read my description correctly, and that the two #6 bare copper and the ground conductor in the cable are connected to the same things in each panel, and they are parallel, and that the #6 is indeed above code and unnecessary.

If it is necessary, I sure would like to know the reasoning behind what it does, and why it is necessary.

OK, go at it!

[Morgans]

No, not fired on account of this case. Probably the same stuff that got him fired, though. I never protested, but I also got off with only promising to put the #6 in, and never did install it. Now, I am bringing everything up to code and want to know what the code says about his extra wire.

What is this ground loop thing? I think that an extra wire connected to the same thing on both panels as the ground wire in the cable would put them in parallel, just like adding extra size to the cable ground conductor, not a loop.