[jhandy]

A home inspector wrote up a violation on a home built in the mid 70's for having subpanels that did not have the ground and neutrals isolated. How is this possible if the panel is fed with a 3 wire feeder? Is this truly a safety issue?

[tkrussell]

Thou I was working in the trade back then, I was just an apprentice and was just learning. The code changes every three years, so it is difficult to remember what may have been allowed back 37 years.

Nowadays, the 3 wire feeder is not allowed to subpanels, and the neutrals and equipment ground must be separated, and a 4 wire system is used to each panel beyond the main breaker.

All thou , for years, dryers and ranges were wired with the same method one wire for both neutral and ground. If existing, they are allowed to remain.

I would like to get the home inspectors answer on if it is safe, hmmm. I trust there would be a detailed explanation of the theory behind the wiring method, and the possible problems it can cause?

The only person that can help in this matter is the local town, city, county, or state electrical inspector, or the authority having jurisdiction over electrical installations.

If the system was permitted and inspected back when it was installed, the chances are very good that was allowed back then, and there is not thing one the home inspector can do to demand a change to a pre-existing installation that passed inspection. The code in effect today does not cover existing installations.

If there is no proof or record of permits back then, perhaps,I am sure someplace, the code that was in effect back then can be found, either by NFPA, or the library, or perhaps the inspector has kept that edition of the NEC.

The issue is a neutral is current carrying, thou because it is grounded at the source, under normal conditions, a shock cannot be felt. With the neutral and ground as one wire, there is a chance, if the neutral is broken, current will try to flow through the equipment ground that is at each outlet and appliance, and here is where there may be a safety issue.

[Washington1]

If the system was permitted and inspected back when it was installed, the chances are very good that was allowed back then, and there is not thing one the home inspector can do to demand a change to a pre-existing installation that passed inspection. The code in effect today does not cover existing installations.

<---this is your answer.

Note: Our jurisdiction has been enforcing the 4 conductor rule since 1993. Before 1993, you where allowed to run three conductors to remote structures.

The 2008 NEC will require 4 conductors. Rather your jurisdiction adopts it or not is up to them. Heck, you guys may be still using the 1999 code! I'm with TK, speak with the AHJ.

[biggsie]

I have some electrical experience and worked for a power company.

From what I know of electricity, a 220 volt line feed the house ---- two hot legs

And the neutral --- all carry POWER... THE NEUTRAL IS NOT A GROUND

I think what they are trying to do is isolate the ground to a grounding steak...

Then a ground is used for electrical boxes, metal fixtures and of course

Grounding GFI's circuit breakers. Less chance of being interupted!!

Have tried to make this easy to understand, if I helped, rate this answer

[tkrussell]

The standard voltage in the USA is 120/240 volts.

The Neutral is not hot, it is grounded conductor, not intended to be a grounding conductor, and is current carrying by carrying the unbalanced current between the 2 live conductors.