I was asked a question and I have my own thoughts. I would like to hear yours. I hope I didn't post this question before, but here goes.

You have a nice 200 amp code compliant service. You want to add a generator so you install a nice big transfer switch with main breaker outside. So you change the service panel inside so that all of your neutrals are separated from the grounding conductors. Now the question:

The range was a 3 wire SEU wire. What happens to the neutral/ground conductor? Leave it with the neutrals? or the ground wires?

The same would occur with a dryer line if/when you used the old SEU wire for that. (Which around here was pretty popular years ago.)

The grounded wire in an old style dryer/range plug circuit using SEU is a neutral being used as a ground. You have created a violation when you put it on a sub panel, even on the 1993 code.

250-60(c) allows using the uninsulated conductor in SEU only if "the branch circuit originates at the service equipment"

OK Greg,

What happens if you want to install a transfer switch before the service and the whole house is finished? there is no way to run a new 3 wire feeder to the stove, then what are you suppose to do? Not install a generator? Or rip open finished walls in a house in order to run the proper cable? Is there a happy medium between the two choices?

Not installing the generator leaves the existing range feed in place. How is that better than allowing existing equipment to be re-connected if it was acceptable at the time of original installation?

Harold:
Sorry for not responding sooner.....BUT

The Rehab Code allows existing branch circuit wiring (range/dryer/etc) to 'remain 'as-is'.

The words are not verbatim but look on page 23-140, dated as revised 11/7/11.

What John said

Generally if this was not in the scope of the new permit, you don't see it. Just like the lack of AFCIs or other things we can allow on the grandfather cause


If you did want a totally compliant new generator installation (all other things being OK;
You could choose to install a sub with transfer equipment for the emergency generator circuits (without the dryer)
or
You could use non-SDS transfer equipment where the neutral is not switched and the main bonding jumper stays in the current service disconnect.
or
You could extend the dryer SEU to a breaker in your new "main" panel. where the service disconnect and main bonding jumper resides.

There may be other solutions too but chances are nobody would ever care if you just left it alone. I do tend to agree that this has always been a potentially dangerous exception, even though we did not really pile up bodies and NFPA did well to get rid of it.

Greg,

Most transfer switches around here only switch the phase legs and the neutrals are almost always left tied together. So this is not a true separately derived system. Another question some EC's ask me is if they should leave the bare stranded neutral/ground on the neutral bar or the grounding bar. Since now the main service becomes a sub panel with a main breaker.

I am going to dig out my Soars grounding book. I think there are some diagrams there that are on point.
I remember Jim Pauley doing about 20 minutes on this is a grounding seminar.

Greg,

I think I have a Soares book around here somewhere.