Natural / ground separation

Can someone tell me which code revision specifically required that the neutrals and grounds in a sub-panel be isolated? Not asking about sub-panels in outbuildings, just sub-panels in the building in which the main service panel is located. TIA

there is no revision for it, it has always been code. most common misunderstanding there is I think. electricians argue it all the time, but there is nothing to argue. I have 6 code books, the oldest being 1960, and yes even before 3 slot grounding receptacles were required the separation of neutral and ground buses after the main has always been code.

code allowed for separate buildings with their own EGC to have a 3 wire feed, and allowed for 240v appliance feeds back in the day to be 3 wire, so electricians made the assumption that 3 wire feed to sub panels was okay for decades due to this, but that is incorrect and they were mistaken. that is why we see so many subs with 3 wire feed.

Here is cut from 1965 code, the last sentence of 250-23(a) highlighted in blue says it all, where “load side” means everything after the main disconnect, its that cut and dry. A reminder for any new guys reading this - grounded conductor is the white neutral, grounding conductor is the bare ground.

**[FONT=Arial][size=2][FONT=Arial][size=2]250-23. Grounding Connections for Alternating.Current Systems.


[/size][/FONT]**[FONT=Times New Roman][size=1][FONT=Times New Roman]size=1 Secondary alternating-current circuits which are to be grounded

shall have a connection to a grounding electrode at each individual

service, except as provided for in Section 250-21. The connection shall

be made on the supply side of the service disconnecting means. Each

secondary distribution system which is grounded shall have at least one

additional connection to a grounding electrode at the transformer or

elsewhere. No connection to a grounding electrode shall be made to the’

.grounded circuit conductor on the load side of the service disconnecting

means, except as provided for in Section 250-24.[/size][/FONT][/size][/FONT]
[FONT=Times New Roman][size=1][FONT=Times New Roman][size=1]

(b) Where the secondary system is grounded at any point, the

grounded conductor shall be run to each individual service. This conductor

shall be not smaller than the required grounding conductor

specified in Table 250-94(a).


[/size][/FONT][FONT=Arial][size=2][FONT=Arial][size=2]**250-24. Two or More Buildings Supplied by a Single Service. **[/size][/FONT][/size][/FONT][FONT=Times New Roman][size=1][FONT=Times New Roman][size=1]Where[/size][/FONT][/size][/FONT]

[FONT=Times New Roman][size=1][FONT=Times New Roman][size=1]more than one building is supplied by the same service, the grounded

circuit conductor of the wiring system of any building utilizing one

branch circuit supplied from such service may be connected to

[/FONT][FONT=Times New Roman][size=1][FONT=Times New Roman][size=1]grounding electrode at such building, and in the case of any building

housing equipment required to be grounded or utilizing two or more

branch circuits supplied from such service, and in the case of a building

housing live stock, shall be so connected.




Good information - thanks. Brings to mind the related question: when was the first electrical code published?

I think the separation of neutral and ground in subpanels was found to be necessary when failure to separate them was discovered to be potentially deadly.

Yes, codes are generally an afterthought. :mrgreen:

From the front of the 2017 NEC:

This is a little off-topic but …

Always? Are you sure about that?

Which code are you referring to?

Who cares when it happened? Inspect the home based on what you know now.

As quoted above in post #2, article 250-23, which I personally have been abiding by for over 25 years of code book use in my profession. I guess I cannot be certain it has always been code since 1899, but every code book I’ve been privy to view so far has it in there

It has not always been in the National Electrical Code.

Then please answer the original posted question and back it up with something like I attempted to do