OT: electical sub panel grounding

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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
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On 10/08/2014 06:24 AM, Morgans wrote:

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.
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Morgans wrote:

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.
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On Wed, 8 Oct 2014 10:49:24 -0400, "Mike Marlow"

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.
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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?
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On Wed, 8 Oct 2014 15:54:43 -0400, "Mike Marlow"

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".
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wrote:

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

"ground loop" means something else in the world of electricity.
John
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On Wed, 8 Oct 2014 22:02:26 +0000 (UTC), John McCoy

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).
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On Wed, 08 Oct 2014 17:24:31 -0400, snipped-for-privacy@snyder.on.ca wrote:

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.

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On Wed, 8 Oct 2014 22:02:26 +0000 (UTC), John McCoy

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
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snipped-for-privacy@attt.bizz wrote in

The situation described has them both in the same conduit, if I'm not mistaken. That's not a loop, that's just two parallel conductors (and, if the conduit is EMT, then it's three parallel conductors).
John
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"John McCoy" wrote
The situation described has them both in the same conduit, if I'm not mistaken. That's not a loop, that's just two parallel conductors (and, if the conduit is EMT, then it's three parallel conductors).
Residential, and not in conduit. This is SE (service entrance cable) and a bare to be copper wire beside the se cable.
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On Thu, 9 Oct 2014 19:54:54 -0700, "Lew Hodgett"

Insulated ground bus (one 's', two and it's a kiss)? Why insulated? It has to be bonded to the case. The neutral has to be isolated from the ground, sure.

The main may be one of the other breaker positions. That is, the sub panel may be back-fed through one of the other breakers, as long as it is clearly marked as the main (disconnect).

Certainly. The wire has to be protected.

Again, why insulated? That makes *no* sense.

If both hots are used, sure. Ground and neutral have to be separated.

*ONLY* if the main is the entrance panel. If it's another sub, they must be separated there, too. In the entrance panel, the grounds need not be separated from the neutrals but it's good practice.

If the main is the entrance.

Lots of other things are required but...
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On Fri, 10 Oct 2014 18:35:35 -0400, "Mike Marlow"

Right, but that's *not* what Lew said. Go back and read what you snipped.

The ground bus is *not* isolated in a common panel. The neutral bus *is* (with a link to bond it in the entrance).
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On Fri, 10 Oct 2014 19:49:06 -0400, "Mike Marlow"

Maybe, but that's not needed, either, if it's in conduit.
OTOH, he said,
"A sub panel requires an insulated ground buss as well as an insulated neutral buss."
The "bus" is the multiple-tap connection point, not the wire between the boxes.
We could also all be talking past each other. I wanted to get everyone on the same page, though.
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"Mike M" wrote
I'm confused by all this, but assuming your feeding your sub panel with three conductors and a ground sized for the OCD then the only reason I can think of for the #6 is that its a separate building and he wants a grounding system which varies from jurisdiction to jurisdiction. #6 being the largest size required to a grounding rod.
MikeM
Remember one of the other comments.
This same inspector was later fired for making people do sh*t that was not required by code. He seemed to invent things along the way.
I suspect if I had reported him with my case, that would have been a few days earlier that he got fired.
There is no reason in the world to require an additional ground. I knew that, (or was pretty darn sure) but wanted to confirm it, and I know there were several electricians in the group.
At any rate, I never did the "upgrade" then, and I'm sure not going to do it now!
Jim in NC
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snipped-for-privacy@attt.bizz wrote in

I wonder if the source Lew was quoting meant an "isolated" ground bus (i.e. isolated from the neutral) rather than insulated.
Because I'm with you, insulated ground bus doesn't seem to make sense, when you're going to strap it to the case anyway.
John
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On Sat, 11 Oct 2014 13:54:01 +0000 (UTC), John McCoy

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-------------------------------------------------------------
"John McCoy" wrote:

If you read and understand what was written, you will see that my comments are correct as written.
The NEC does NOT permit multiple paths to ground, but rather only allows a single path between a fault and earth ground.
INSULATED neutral buss and ground buss bars mounted and wired ONLY as described will meet those NEC requirements of having ONLY a single path from fault to ground.
Yes it does make a difference how a system is wired and the equipment used in order to meet the NEC requirements.
Lew
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