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Main Panel: Neutral-Ground


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I saw a 200 amp main service panel in an attached garage today. There was no exterior disconnect.

The panel had neutral busses on each side and ground busses on each side. (Like a subpanel would need) The ground busses were isolated from the neutral and the service conductors, including the main grounding conductor were all in correctly.

So far so good.

All of the house circuit's ground conductors were connected to the left grounding buss and all the neutrals were connected to the right side grounding buss.

The neutrals from the house were isolated from the main service neutral.

I reported to my client that I did not believe this was proper and that the house circuit neutrals should have been connected to the neutral buss/es, and that it should be fully evaluated by a qualified electrician and corrected as necessary.

I am not an electrician and would like to have a better overview on this.

What are the possible hazards if these neutrals are grounded but isolated from the service neutral like this?

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Hi J,

This is a great site, freequented by loads of friendly and smart people. They're very approachable and most are willing to answer your every question, or at least try to point you toward someone who can.

But we follow a certain personal model here. Your username and profile are empty, except for a letter. The message that sends is: "Hello, I'd like some of your knowledge, but I'm unwilling to tell you anything about myself." Fill in your profile a little, and watch the replies come rolling in.

Welcome aboard,

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I hate to be a killjoy gentlemen, but perhaps you should give new guests a chance to become accustomed to our...unusual...sense of humor before exercising it on them. It's just possible that they won't get the joke immediately, y'know. One might think such statements are in poor taste, if they didn't know better.

Brian G.

Wet Blanket

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Originally posted by hausdok

You say that the ground busses are isolated from the neutral and service conductors, but that all were in correctly. This is a main panel. Are you saying that there was no bonding jumper, screw or strap connecting any neutral bus to the panel enclosure? If they were in "correctly" the neutral busses had something bonding them to either directly to the ground bus or the enclosure.

J,

Sometimes the bond isn't obvious, like big-headed green screw or a jumper bar. When in doubt, whip out a meter and check continuity with the ohm range. It'll tell you whether there's really a connection or not. Don't assume anything, find out.

Brian G.

ohmmmm...ohmmmm...ohmmmm...(meditation for electricians)

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Hello guys,

Thanks for clarifying forum etiquette for me. I have modified my profile but will fess up on this note as well.

My apologies but I don’t know you guys good enough to show you my girlfriends picture yet!

I'm Mark Bishton. I have a one man inspection shop in Southern Indiana called Benchmark Home Services. I've worked in the home building business for over 30 years. Started as a grunt on a framing crew in 1970. Became sole proprietor of a small projects construction company in '78; incorporated in '82 and started building turnkey custom homes. I have been designing homes since '88. I joined ASHI in '96, then stopped building and started inspecting in 1998.

Now that you know way more about me than you probably wanted, I'd like to get my question cleared up and answered.

Funny how 53 years of trying to speak good English doesn't always get the job done! Can’t ever slack up!

I tried to clearly describe this panel but should have also said, that there was no bonding screw, strap, etc.

I should always be wary about using the word ‘correctly’; I guess that I tired of describing.

So.... the bottom line of my question is this: When the neutral wires of various appliances and house circuits are connected to ground and not neutral what is the hazard? Is it a shock hazard or a fire hazard or an equipment hazard or is it just like me 'different'?

Mark

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Originally posted by J

I tried to clearly describe this panel but should have also said, that there was no bonding screw, strap, etc.

Ah, but I'm afraid that alone does not neccesarily mean it's not bonded. Using the technique I described earlier, I've found bonds where none were visible (and confirmed no bond at all in 2 or 3 cases).

So.... the bottom line of my question is this: When the neutral wires of various appliances and house circuits are connected to ground and not neutral what is the hazard? Is it a shock hazard or a fire hazard or an equipment hazard or is it just like me 'different'?

Looking back at your original post, I'm still not quite sure I'm with you. Are you saying:

the neutrals from the house circuits are isolated on an equipment ground bar, i.e. "grounded", but not connected to the service neutral in any way?

If so:

How do you know whether that bar is really grounded or not? Is there a ground wire run directly to it, or is the ground via the bond with the enclosure and the other equipment ground bar which has the ground wire?

Douglas, Mark, or Lord Jim,

If the neutrals were connected to one isolated equipment ground bar (isolated from the service neutral), which was connected to another equipment ground bar with all of the equipment grounds, what would be the potential danger? Wouldn't we be putting some current on the equipment grounds, possibly electrifying all grounded metal casings, etc. if the true ground were lost?

This is making my head hurt, I must be thinking.

Brian G.

Picking at the Knots

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Originally posted by J

. . .

So.... the bottom line of my question is this: When the neutral wires of various appliances and house circuits are connected to ground and not neutral what is the hazard? Is it a shock hazard or a fire hazard or an equipment hazard or is it just like me 'different'?

Mark

I'd say it's all of the above, but just barely. Here's my take on it:

When the grounding and neutral conductors in a sub panel are connected to each other, the electricity has a choice of which way it gets back to the main panel. Some of it passes back through the neutral conductors; this is safe, since these wires are insulated and people are unlikely to touch them. Some of it, though, passes back to the main panel through the grounding conductors, energizing every grounded surface and object along the way. These may including the metal jackets of appliances, the outside of metal conduits and, sometimes even metal water pipes. In most cases where this happens, people don’t feel the electricity or get shocked because their bodies are not grounded well enough to entice the electricity to travel through them. However, if someone were to become exceptionally well grounded or, more dangerously, if a grounding conductor were to become disconnected, a great shock hazard would exist.

Furthermore, since the returning current is split up among many different paths, the current on any one of them is imbalanced. This means that the magnetic field that it generates won't be fully cancelled out. In some circumstances, this field can get to be quite strong and will interfere with electronic equipment including TV or radio reception. Worse yet, if it's a conduit system, the conduit could heat up due to inductive reactance.

In the real world, it rarely causes serious problems. But it's nice to know the whys and wherefores of the stuff we call out.

And before anyone asks, regrounding the neutral beyond the main service has been prohibited by the NEC since 1923 according to Douglas. Though, I've heard rumors that the 1917 edition also had the provision. I'm not really certain, my oldest copy is from 1947 and it's clearly prohibited in that one.

- Jim Katen, Oregon

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Sorry to have created a confusing question.

Lets try it again.

Forget all that I have said before.

I saw a 200 amp main panel in a garage. There was no other disconnecting device between it and the meter.

This panel had 4/0 Alminum service conductors wired into the service main breaker and neutral buss connection. The neutral busses were isolated from the panel box.

There were two ground busses, one on each side of the panel box, bonded directly to the panel box. (This is to say they were isolated from the neutral busses and neutral service conductor.)

A #4 bare copper grounding conductor was connected to the left side ground buss. All the house circuit ground wires are also connected to this ground buss.

The right side ground buss is connected to the left side ground buss by the conductivity of the main panel box.

Now this is what appears to be incorrect!!! The neutral wires from the house 110 & 220 V circuits are connected to the right side ground buss. They are not connected to either of the two neutral busses. Nothing is connected to the neutral busses except the main service conductor neutral.

It would appear the all overcurrent traveling on the house neutrals would go to the ground buss and would only energize house circuit grounds with the electricity that cannot fit on the #4 copper main panel grounding conductor.

I don't have a good enough overview of real time normal current loads and load balances to have a feel for the potential risk here.

Jim Katen reports that "regrounding the neutral beyond the main service has been prohibited by the NEC since 1923" so I guess that may be what has happened here, then again it has happened in the main panel so is it really beyond the main service?

In answer to Brian, yes if the main panel ground conductor system failed the service neutral would not be there to be a ground or neutral path and every grounded appliance cabinet would be looking for somebody to provide 'ground'!

My question was what risk does this configuration create without any part of it failing or loosing connectivity?

Mark Bishton

Bloomfield, Indiana

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Originally posted by J

My question was what risk does this configuration create without any part of it failing or loosing connectivity?

You'll definitely want to wait on Douglas, Jim, or Mark on this, but I suspect the answer is "none". Even if that's the case, the larger problem is that electrical safety is designed to be in over-lapping layers. As I understand the situation, your client is only 1 layer away from a life-threatening hazard existing in several areas of the house. Forgive me, but I assume this is an intellectual exercise on your part, not a question as to what to report or recommend to your client, yes?.

Bt the way, what brand was the panel? I've never seen one set-up as you've described, so I wonder if it was altered on-site for some unknown reason.

Brian G.

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Originally posted by Douglas Hansen

One other aside - and please don't take offense - the word "buss" is synonymous with the word "kiss." When we talk about electrical bus bars, there's only one s in bus.

You mean all of those fuses I sold were actually "Kiss" brand?!

Brian G.

Yuk-Yuk!

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Originally posted by J

Sorry to have created a confusing question.

Lets try it again.

Forget all that I have said before.

I saw a 200 amp main panel in a garage. There was no other disconnecting device between it and the meter.

This panel had 4/0 Alminum service conductors wired into the service main breaker and neutral buss connection. The neutral busses were isolated from the panel box.

There were two ground busses, one on each side of the panel box, bonded directly to the panel box. (This is to say they were isolated from the neutral busses and neutral service conductor.)

A #4 bare copper grounding conductor was connected to the left side ground buss. All the house circuit ground wires are also connected to this ground buss.

The right side ground buss is connected to the left side ground buss by the conductivity of the main panel box.

Now this is what appears to be incorrect!!! The neutral wires from the house 110 & 220 V circuits are connected to the right side ground buss. They are not connected to either of the two neutral busses. Nothing is connected to the neutral busses except the main service conductor neutral.

It would appear the all overcurrent traveling on the house neutrals would go to the ground buss and would only energize house circuit grounds with the electricity that cannot fit on the #4 copper main panel grounding conductor.

I don't have a good enough overview of real time normal current loads and load balances to have a feel for the potential risk here.

Jim Katen reports that "regrounding the neutral beyond the main service has been prohibited by the NEC since 1923" so I guess that may be what has happened here, then again it has happened in the main panel so is it really beyond the main service?

In answer to Brian, yes if the main panel ground conductor system failed the service neutral would not be there to be a ground or neutral path and every grounded appliance cabinet would be looking for somebody to provide 'ground'!

My question was what risk does this configuration create without any part of it failing or loosing connectivity?

Mark Bishton

Bloomfield, Indiana

Mark,

Sorry for misunderstanding your original post, I'm afraid I answered a question that you didn't ask.

It sounds from your description like the system is returning current to the transformer through the earth. As Douglas said, this will produce very unsatisfactory results. (Though out here in the sticks, I once saw a well pump powered with a single wire, using the earth as the return path. It worked, but I'll bet that the motor was not a happy camper.)

However, I'll bet that if you look carefully at those factory-installed neutral terminal bars, you'll find a bonding screw somewhere.

Seimens panels can be set up exactly the way you describe with a couple of accessory grounding terminal bars. They have a bonding screw at the upper right bar.

- Jim Katen, Oregon

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Originally posted by Jim

However, I'll bet that if you look carefully at those factory-installed neutral terminal bars, you'll find a bonding screw somewhere.

I think that's a good bet, but at the risk of repeating myself into a horses' a** I will say again that it is not wise to trust a visual on this. The only way to know is to check continuity; all else is guess-work.

Personally, even if I found the neutral bars were bonded I would still recommend moving the neutrals to the correct bar. I would want all of the available layers in place before everyone walks off and forgets about this panel for who knows how long.

Brian G.

Horses' A** & Inspector, But Not a Horses' A** Inspector [:-mischievous]

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  • 5 years later...

250.24. Grounding Services

(A) Grounding Neutral. Alternating-current services that are supplied from a grounded electrical system from the utility must have the grounded (neutral) conductor connected to a grounding electrode of the specified in 250.52 in accordance with Part III or Article 250 in accordance with (1) though (5). See 250.24©.

This clearly states that the neutral of the service must be connected to earth ground.

Does it state anywhere that this connection MUST be made in the panel, or can you have separate grounding rods for each buss, neutral and ground?

Due to the electronics in the house, I would rather the neutral and grounding conductors were as separate as possible.

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