Bonding on a 3 wire subpanel?

Had this in the emergency section, but not much reply: thanks
So had an old Wadsworth panel today, there are obviously some defects, but my main question is about the bonding. The pic doesn’t show the whole thing, but there is a service panel (with only the 100 amp shut off breaker) next to this subpanel, and behind the service panel is the meter on the other side of the wall. The meter has the grounding conductor to a rod.
Since this is a 3 wire feed, the grounds and neutrals are on the same bus. BUT there is a metallic path to the meter, correct? (The connector ring between the two panels). Which means it is already bonded to the meter… Does this change the rules? Shouldn’t this sub panel now need to have the neutrals isolated, even though it is a 3 wire?
I also see a scorch mark on the main service neutral…


Yes, the metallic conduit (nipple in this case) between the meter box and the service panel will create a neutral parallel path and is not recommended. However, it is an accepted practice in many locations and unless your local codes or AHJ prohibit it, I would not call it out. It does not make the panel with the first disconnect a sub-panel, so bonding of the neutral bus is necessary and you don’t have to separate neutrals from grounds.

The subpanel (in pic 3) needs its neutrals separated

Since there is a service disconnect between the meter and the panel the neutrals and EGC’s in the panel must not be landed on the same bus. There should be a separate bus for each and the neutral bus must be isolated from the enclosure. Since there is a metal nipple that qualifies as an EGC between the panel and the disco this is technically a “4 wire” feeder.

Thanks, Simon,
yes, that’s the one I was referring to, just wasn’t sure since it was only a 3 wire feed, and not 4. Because on 3 you typically don’t separate, unless metallic path, right?

Unless on a 3 wire feed, right? (Like this has?)

The equipment grounding (what the 4th conductor would do) to the subpanel is provided via the metal nipple of the service panel.

This is only true for subpanels in remote buildings prior to 2008 and if there are no metal paths between 2 buildings.

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That’s what I thought, just wanted to confirm… Thanks!

I don’t know which rules you are talking about and I don’t understand you comment about changing the rules.

There is a metallic path but it is not necessarily properly bonded. If there are any impaired mechanical connections, such as concentric knockout rings, a bonding jumper is needed at each impaired connection.

The distribution panel (sub-panel) should have the grounded conductors separated from the grounding conductors in the panel. It is not necessary to isolate anything.

A bonding jumper would not be required at 120/240 volts.

Are you saying 250.92(B) does not apply to 120/240v systems?

Isn’t this a sub-panel and not a service? There is a service disconnect between the panel and the meter.

There is a metal nipple between the meter enclosure on the outside and the main disconnect enclosure on the inside, is that covered by service?

Yes, that is on the line side of the service 100 amp OCPD so standard locknuts are not permitted to provide the bonding for that nipple. The nipple on the load side between the 100 amp main and the panel does not require anything other than a standard locknut even if there concentric or eccentric KO’s. My comment was directed towards the fact that the concentric or eccentric KO’s do not make any difference in the bonding requirements of that nipple.

Thanks, I thought you were saying in general, wanted to make sure I wasn’t losing my mind :slight_smile:

BTW, do you have a problem with a metal pathway between meter and service panel? as opposed to using PVC conduit in new construction? that fact that it’s a short run eliminates all potential issues that could arise? Sometimes I find a jumper cable going from meter metal conduit on the outside to service panel, paralleling the neutral.

No you’re not losing your mind my initial post wasn’t very clear so I apologize for the confusion.

Regarding your question, yes a PVC raceway between the meter and the service disconnect would eliminate objectionable current but since metallic raceways are permitted to be used between the two enclosures this is one time where the objectionable current is actually permitted by the NEC because it cannot be avoided. Now if there is a jumper connected between the two that would (as you stated) be parallel to the neutral and that would not be permitted due to 250.6(B).

sorry, When I say ‘isolate’ I meant Separate. And the “rules” were referring to the grounding means between 3 and 4 wire feeds. My concern was that since it was a 3 wire feed, the grounded and grounding can be on the same bus, unless grounded by other means. Robert explained it with the nipple creating the EGC, making it a 4 wire feed. Thanks!

A bonding jumper is required where there is an impaired mechanical connection between the meter base and the Service Panel.

That was my understanding as well… no Myer’s hub on concentric or otherwise impaired. I’m curious to learn more about this. I very rarely see a meter face & disconnect that only serves as the service and there’s no branch or other ocpd’s.

Something beyond a standard locknut (bonding bushing, bonding locknut, bonding wedge) is required to bond the metal raceway on one end when it contains service entrance conductors, which in your example it would be required.

I was referring to the metal nipple between the 100 amp service disconnect and the panel. Since it’s less than 250 volts to ground even with concentric or eccentric KO’s a standard locknut is all that’s required for the bonding of that nipple.

So that has got me thinking, since we are on the topic, what about this. This was built in 2013, but I don’t see any EGC anywhere. This service panel is in the garage, and the meter is outside, but on a different wall. Is this missing a jumper or EGC? because it only has the 3 wire feed, even from 2013?