I am seeking the knowledge of when did the NEC require sub panels to have separate neutrals buss and ground buss (and the panel bonded to the ground only). I would think this has been a requirement since 1993 but can not confirm. Please advise
JoeMed@cableone.net

NEC does not define "main" or "sub" panels.

It has been required to segregate the neutral from the ground downstream from the service over-current device since the two both existed, or since Ben Franklin was flying kites, whichever came first.

I'll forgive you, though, as the NEC has refined its' language regarding grounding quite a bit recently. It was not unusual for three experts come up with three mutually exclusive readings of the code. The code itself has been somewhat contradictory and confusing- put it down to poor literacy on the part of engineers trying to be lawyers!

Nor will I dispute that many, many places have "ancient" panels wired wrong. That doesn't make it right.

Thank you, I believed this to be the case but I not having older NECs or knowing how long said code has been in existance is difficult. Yes, this is one common installation mistake I see frequently.

In older Code issues it was in Section 250-23. The oldest Code I have, 1931 has it in section 903. "The grounding connection shall be made at the transformer, generator,...on the supply side of the first switch controlling the system." Seventy five years and they still get it wrong. Alan - Inspector.

Thank you, Alan. Old code books are rare as hen's teeth.

Here's a quote from the 1911 NEC. Pg 25, Section 15 "Grounding Low-Potential Circuits". (FYI low potential was defined as 550 volts or less). Sub title "Alternating-Current Secondary Systems"
b,3."The ground connection must be at the transformers or on the individual service as provided in sections c to g, and when transformers feed systems with a neutral wire, the neutral wire must also be grounded at least every 500 feet."
Notice the requirement to ground the neutral every 500 feet.

Steve thanks for the follow up, and most unusual installation. I'm going to think about that for a while.

Take a look at the 2002 NEC 250.184(D)(3) keep in mind this is for systems above 1KV.


Steve is it possible that the 1911 NEC. Pg 25, Section 15 was referring to a multigrounded neutral system. The same system the power companies use today.

Thanks for a look into the 1911 NEC.

Bob

A ground installed every so many feet is very similar to the PME (Protective Multiple Earthing) system used in Britain. While originally employed only in certain rural areas, it's become much more common in recent years, and in fact most LV distribution networks are now PME equipped (all in my local area, so I have been told).

The multiple grounds are only on the distribution network though. Once past the meter on a service, N and G are kept strictly separate.