Residential service with two panels - separated neutrals/grounds in each panel?

[bdn2004]

A homeowner has a 300A service that comes into a meter base on one end of his house and it splits off to two separate panels, one in his main house about 50'away and the other to another panel in a detached garage about 75' away. The ground rod is located at the meter base. They used a service type panel with neutral bars along the sides and all the neutrals and grounds are on the same bars.

It was recently inspected and he was told that in the house panel that the equipment grounds and the neutrals are insufficiently separated.

We are trying to figure out what he is talking about. My theory is is that the ground and neutral is bonded at the meter base and therefore can't be tied together again. Any ideas? And is there an easy fix?

 

[dpc]

So there is no main disconnect at the meter?

 

[waross]

There should be a neutral buss and a ground bus. All the neutrals on the neutral bus and all the grounds on the ground bus. At one common point the ground must be tied to the neutral and grounds and neutrals must be separated downstream. There is generaly a screw or a jumper connecting the ground bus and the neutral bus. This must be removed in all sub panels.
If there are two neutral buses you may be able to remove the connection between them and use one for a ground bus. Check with the AHJ before making any changes.
Panels with common ground and neutral bus are common in some countries in Central America.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[bdn2004]

This particular panelboard there doesn't look like the neutral and ground can be seperated. The three wires, L1, L2 and Neutral come into the top, neutral in the middle. The neutral is attached to a bus that is connected to the screwed terminal strips running vertical down the panel.

Looking at the circuit the neutral in between the main and the first panel would be carrying ground current in the case of a fault. But I'm thinking that's what the Utility does..., they don't have a seperate ground wire. So what's the hazard?

That's good advice to talk to AHJ first before making changes. This house passed electrical inspection.

As a fix I was thinking we would have to buy a seperate ground bus with a big lug on it to connect a seperately pulled in wire. Then re-wire all the grounds from the branch circuits to this bus.

 

[bdn2004]

What we are essentially being told to do is trade a #2/0 neutral which would carry the ground current, to a #4. That doesn't make much sense to me. Am I missing something here?

 

[gobigorgohome]

You need to consider the bigger picture. When you consume power through L1 or L2, the circuit must be completed with a return path. The neutral.

Current comes in on L1 or L2 and goes out on the neutral.

Great. The ground conductor is there as an emergency path for a wayward L1 or L2 that gets shorted to something metal. Not the normal return current.

The problem with connecting the ground to the neutral again at the 2nd or 3rd panels is that everyday return current will flow through both the ground wire and neutral wire. So what? Remember that everything metal that is "safety grounded" is now hooked to a midpoint neutral connection that by the very nature of ohms law will become energized (compared to the pole ground)as load current increases. Tingling (shock) is the result. And worse yet, a line to neutral fault causes the voltage from the safe ground conductor to rise further above earth potential. This results in what is known as step and touch potential that can kill.

99% of electrical panels have seperate neutral and ground busses. Typically the ground busses are fastened to the metal box, and the neutral bus is insulated from the metal box. Suppliers put a jumper between the two, so that you can bond them ONCE at the service entrance. Otherwise the jumper is removed for subpanels.

For further reading search for a whitepaper called "Grounding: the Good, the Bad, and the Stupid"
Donald Zipse
Electrical Forensics, LLC
and "Death by Grounding" by the same author.

 

[dpc]

At one time, the NEC allowed co-mingling of ground and neutral conductors in service entrance panels. Something that passed inspection at the time of construction might not be wired in accordance with the current code. If the panel is not a service entrance panel (after the main bonding jumper), then it was never allowed to connect the green ground wire to the neutral bus or vice versa. If there is a main disconnect ahead of these panels, the main bonding jumper will be there and the neutral and ground buses must be separate in both panels.

 

[bdn2004]

Attached is a sketch of how I think things are connected and how it would work now. I'll have to modify it for another. I can see how the other line L1 in this case may have some cancelling effect on a fault...but this would seem minimal to me.

 

[dpc]

Based on your sketch, both of the panels would be sub-panels so there must be separate ground and neutral buses in each, and the white and green wires must kept completely separate from each other. There should be a main bonding jumper where the two main breakers are located. This would be the requirement for new construction.

See Article 250.32 in the NEC. You probably need a grounding electrode at each of the panels if these are in separate buildings or structures.

When it comes to NEC compliance, you really cannot use common sense, engineering judgement or laws of nature - you just have to do what the NEC says (or what the local AHJ thinks it says).

 

[bdn2004]

Just for the record the attached sketch is what we are going to end up with. There is not a seperate ground and neutral bus in this panel. We can buy one however and will mount it in there and run another ground wire to each panel.

The outbuilding panel does have another ground rod. BTW at the outbuilding we are NOT to tie the neutral and ground together there either right? Just this additional ground rod?

 

[dpc]

This is not a typical service arrangement. What I would do in your position is go discuss the situation with the electrical inspector ahead of time. See what they think is required and then install it that way. Trying to outguess them can get expensive, especially for retrofit like this. In the end, it will be done the way the inspector wants it anyway.

 

[bdn2004]

The thing of it is...this is an existing installation that has come to a head because the house was sold. As is routine the buyer requested a home inspection. The "home inspector" found this situation - there is nothing legally binding with him. And it's not going to be re-inspected by the County Building Inspector.

If we can fairly easily correct to meet Code...we'll do it, everyone will be happy, and the new Owner won't have to bother with it if he sells the house. A ground bus bar for this panel is about $7 dollars at Home Depot.

 

[dpc]

If you are going to work on it, you (legally) need a permit and an inspection. It's a Catch-22. Once you start working on it, it will have be brought up to meet the current NEC requirements, (subject to the whim of the AHJ). Since this involves a sale, I'd get a licensed (and bonded) electrical contractor and let them take care of it - or give you an estimate. Then the contractor will take care of dealing with permits and inspector and you'll have someone to sue if the house burns down or someone gets electrocuted.

 

[bdn2004]

We do have a licensed electrician who will do the job. I'm not doing it. I found out the price of the part because I don't want the owner to get hosed in case the price is big $$...it should not be.

And I did talk to the County Building Inspector, and he without looking at it, said he understood what I was talking about and agreed and would probably go along with not doing anything. After all they did sign off on the installation before. But we don't want to not have it at present Code cause who knows who may say something different in the future.

 

[dpc]

If it was my house and a sale was not pending, I might not do anything - it's been working for a long time. But when a sale is involved, it gets a lot more complicated - as I'm sure you know. Sounds like you've got it covered. The electricians generally have an easier time with the inspectors than Joe Citizen.

 

[VladChiefns830]

bdn,

No offence but - if you don't understand about separation of neutrals and grounds, and when to and when not to, and how to and how not to, you are probably not qualified to do it, or even to assist. I would consult a qualified electrician and in that manner you can be of help.

That being said - the neutral and the ground are identical up to and including the panel that has the MAIN SERVICE DISCONNECT. Any panel downstream from the main panel must have an extra (grounding) conductor as part of the feeder and all neutrals and grounds at the downstream panel(s) must be kept entirely separate from one another.

Again - if you are not sure you can really hurt someone. Mistakes in this area are rather common. If you need help at least consult with the inspector who is telling you that it is incorrect, make a call, stop in his office.

 

[waross]

If you are in Canada the code is a little different. A panel in a separate building is considered as a service entrance and the neutral bus must be bonded to the ground bus. There must still be a separate ground bus and a grounding electrode(s) must be installed. On the plus side, there is no need to run a grounding conductor to the separate building. (The last time I checked.)

Bill
--------------------
"Why not the best?"
Jimmy Carter