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Bonded again at 'main panel'?


montana
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Would like some support if I'm right, and correction if I'm wrong. About to enter a discussion with an electrician over this.

Meter and service entrance panel are installed on exterior of house. This panel is grounded and bonded.

Inside the wall is the "main panel' (or what I would call the main distribution panel). Three conductors come in through the back of the panel, the 2 hot service conductors, the 3rd service neutral, AND a bare grounding wire that attached to the left bus bar - which is attached to right bus bar, which has a bonding jumper to back of the panel enclosure. Equipment grounding conductors and neutrals terminate at both busses. To me, this means that this 'sub panel' (main distribution panel), has been bonded a second time.

Hitch - it had been approved by the local state electrical inspector (now retired). The electrician that I am talking to says that the current state electrical inspector approves this setup on a regular basis (which is why he refuses to sign his name to something that says it is safe, which is all that I asked for in my report anyway).

See pics. Now - is anything wrong with this picture(s)?

IF it is wrong, then what is the danger?

Using NEC 2005 (current code at time of construction), I am looking at sections:

250.24 (A)System Grounding Connections

section (5) Load-Side Grounding Connections

and

408.40 (3rd paragraph)

I am weak on theory. Can anyone provide some some clarification on what is the real danger? It makes good sense in panels in detached buildings, but when it is a "sub" panel is being bonded when the service entrance panel is 6 inches away on the exterior side of the wall? Some of this seems somewhat arbitrary.

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tn_2010729224416_maindistribution.jpg

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tn_2010729224528_bonding%20jumper.jpg

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Thanks ahead of time,

Terry (Montana)

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First, I assume there is a disconnect in the exterior service panel, above the area in the photograph.

You are technically correct, and can add 250.142(B) to your list of code violations on this setup. However, it poses no danger (this time).

Current will travel on the neutral conductor between the panels. Because the neutral is bonded, there is also a path for current on the bare grounding conductor. If there is a metal chase nipple between the two panels, there could also be current on that metal. So we have to ask, how much current, at what voltage, and is it a danger?

The amount of current intended for the neutral feeder is equal to the load imbalance between the two hot conductors. The voltage on that neutral, at the point where originates in the subpanel, is going to equal the voltage drop from there to the utility transformer, and (absent loose connections) is going to be very low (probably less than one volt). The grounding conductor and the metal enclosures are now going to carry some of that current, but there isn't ever going to be enough voltage potential between the two enclosures for that to cause a problem. It will be so low as to not be measurable with normal test equipment.

The further a subpanel is from the service, the more hazards you can introduce by re-bonding the neutral. It might be possible to have current traveling on water piping or other things not intended for current, and the voltage drop on the neutral can sometimes be great enough for the voltage differences to be perceptible. When panels are back-to-back like this, the code is still the same, but the dangers are so low that it is common to have folks like your state inspector signing it off.

Home inspectors must pick their battles. A better one to pick here is the violation of 408.41, where the neutral conductors are sharing terminals with grounding conductors. At least that is what I think I'm seeing in the third photo.

I see you are not a frequent poster here. This forum has technical moderators who are experts in their subject matter, and the one for this section is Jim Katen. I am only answering this because he seems to be engaged elsewhere this evening, and your message implied that you needed an immediate answer. Welcome to TIJ.

Douglas Hansen

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Are you THE Doug Hansen, co-author of "Electrical Inspection of Existing Dwellings". I loved your book, and have re-read it front to back many times over the years. Good job man.

Yes, the first pic includes the main disconnect and the meter.

Thank you for your well-reasoned and patient answer. What you say does make sense, and it helps a lot.

I had called a different state inspector on this same question two or three years ago. and he said something similar, but also stated that even with an arrangement like this that there was some chance that the breakers might not operate properly (I couldn't follow his logic on that one).

As to your other observation, except for one particular electrician, ALL the approved panels I have seen around here have always allowed multiple neutrals and/or grounding wire to share terminal screws. That one has bothered me too, but like you said, I have to pick my battles - especially around here, a rural area. Unless I am working in the city to the north of me, except for the state electrical inspector, there are no inspections. So imagine what I see for structure, heating, plumbing, and the list goes on.

Thanks

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Douglas's answer is precisely correct. I wish he'd participate more often.

To give a broader perspective, I'll offer an alternative conclusion though:

While the lack of separation between the grounds & neutrals isn't likely to cause a problem in this particular case, it will present a conundrum for the next home inspector who comes along. It would take the electrician about 30 minutes to correct the issue and make the service fully compliant with the NEC. I suspect that it would take him longer to write the letter that you asked for.

Most electricians charge a minimum fee to visit your house. I bet that an electrician could fix the 408.41 issue and the ground/neutral separation issue in under an hour for a very modest fee.

I believe you're mistaken about the load centers allowing multiple neutrals. Read them more carefully and I think you'll find that they allow multiple grounding conductors, but not multiple neutral (grounded) conductors.

On a philosophical note, I don't believe that we have to engage in battles at all. I discourage my customers from asking the sellers to make repairs to the house. In a case like this, I'd advise the customer to wait until he owns the house and then hire his own electrician to make improvements to the system. When that happens, there is no battle, the work is generally done properly, and the outcome is more satisfactory in every regard. The whole notion of battles comes from the notion that sellers should pay to improve their house at the request of a buyer. I find that whole paradigm to be absurd. Once it's abandoned, everything becomes easier.

- Jim Katen, Oregon

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Jim,

Thank you for YOUR reasoned and patient reply too.

My inspection reports contain standard language in my Definition of Terms page that essentially states something similar to what you said. Guess nobody reads that part of the report. Now, if I can just communicate it properly to folks tomorrow, we'll all be winners.

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