# Grounds and Neutrals at Separate Buildings



## jar546 (Apr 14, 2019)

There have been some changes over the last few code cycles concerning the requirements of separating grounds and neutrals after the service disconnect.  I am not talking about separately derived systems just to clarify.  The 2014 and 2017 are almost identical.  The major change came in 2011 and started in 2008.  OK, enough of a history lesson.
This code (250.32(B)) is one of the few that actually allows a previous installation to stand even if modified today if certain criteria are met from a compliant installation from a few code cycles ago.
Let's break this down:

250.24(A)(5) requires that grounds and neutrals be separated after the service disconnect.  That is one fairly steady, hard rule.  This would also apply to any subfed panels at separate buildings or structures, even though they are required to have their own grounding electrode system (250.50).

For new installations all separate structures and buildings must have their own grounding electrode system but it cannot be connected to the grounded conductor (neutral) which must be separated from the enclosure and equipment grounding conductors.  The new grounding electrode conductor for the separate building will be bonded to the equipment grounding system.  Again, I am not talking about separately derived systems.

So even though you will see a grounding electrode conductor entering a main disconnect for the building, the neutrals and grounds must still be separated.  This is often an area of confusion when inspecting.

When do we need to run a separate EGC for feeders to buildings and structures?  Always per 250.32(B)(1) with 2 exceptions.  The first exception would be if ALL of the following criteria were met:

_Exception No. 1: For installations made in compliance with previous
editions of this Code that permitted such connection, the grounded
conductor run with the supply to the building or structure shall be
permitted to serve as the ground-fault return path if all of the following
requirements continue to be met:
(1) An equipment grounding conductor is not run with the supply to
the building or structure.
(2) There are no continuous metallic paths bonded to the grounding
system in each building or structure involved.
(3) Ground-fault protection of equipment has not been installed on
the supply side of the feeder(s).

If the grounded conductor is used for grounding in accordance with
the provision of this exception, the size of the grounded conductor shall
not be smaller than the larger of either of the following:
(1) That required by 220.61
(2) That required by 250.122_

Pay particular attention to exception 1 (2).  _There are no continuous metal paths bonded to the grounding system in each building or structure involved_.  So, if they ran metal conduit between buildings or if there is a metal or gas water pipe that is bonded and runs between buildings OR if the buildings are attached with a metal structure.

The second exception basically points to separately derived systems so unless you have a service or source neutral that is switched with a disconnect or like device, you don't have to worry about it.

Thoughts?  Additions, corrections?  Clarifications?


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