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Discussion Starter · #1 ·
I am currently updating a subpanel in a multi-family dwelling. There are four units connected with a four gang meter base about 100' away. There is no practical way of getting from this unit to the meter base. The subpanel currently has a three wire feeder. There is access to the water pipe under the unit. In this case can I run a ground to the water pipe (copper) as it comes in the unit from underground and bond the grounded and grounding conductors at the new subpanel?
 

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You can't do what you are proposing, however, you can reuse the 3 wire feeder if you are simply replacing the sub and all the conditions of the exception are met...

(B) Grounded Systems.
(1) Supplied by a Feeder or Branch Circuit. An equipment
grounding conductor, as described in 250.118, shall
be run with the supply conductors and be connected to the
building or structure disconnecting means and to the
grounding electrode(s). The equipment grounding conductor
shall be used for grounding or bonding of equipment,
structures, or frames required to be grounded or bonded.
The equipment grounding conductor shall be sized in accordance
with 250.122. Any installed grounded conductor
shall not be connected to the equipment grounding conductor
or to the grounding electrode(s).
Exception: 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
 

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Discussion Starter · #4 ·
So what does that mean in English? Is that saying I can bond the grounding and grounded conductors in the subpanel and not tie anything to the water pipe? The feeders are run in flexible metallic conduit. I can break the metallic bond, though. I am replacing the subpanel and adding a few circuits.
 
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