On Sun, 9 Jun 2019 22:39:34 -0500, Terry Coombs
wrote:

On 6/9/2019 9:40 PM, wrote:
On Sun, 9 Jun 2019 20:01:54 -0500, Terry Coombs
wrote:

Â* When is it necessary ? I've just replaced the panel out in the shop
(aluminum buss bars on the old one were giving problems) and I have a 3
wire service run out there . At this time the only place the neutral is
bonded to ground is in the meter box . It has been suggested to me to
bond them in the main panel too ... but that seems redundant to me ,
they're only the thickness of a piece of plywood apart . I have
considered installing a ground rod at the new panel but am concerned
about the potential for ground loop currents .
If you only have 3 wires in the feeder going to the shop you need to
bond the neutral and ground out there too or there is no path for
fault current. You also need a ground electrode out there. Current
code requires a 4 wire feeder and isolating neutral and ground in sub
panels but if the wire was already there when the 1996 code was
adopted the 3 wire feeder is grandfathered in.
Ground loops are not an issue but carrying circuit current in the
grounding conductor is, That is why you do need another ground
electrode. Essentially you are creating another service in the second
building and creating a new ground reference there.
In the electrical biz, you can't have too many ground electrodes but
they all need to be bonded together.


Â* OK , that makes sense . I'll need to drive a rod and run the ground
wire into the box . I can put it in the hole thru the concrete floor
that the service feed comes up through . And I just happen to have the
ground rod and wire from when I pulled out the temp service pole . I
considered using the metal carport frame , but that might be dangerous
under certain dry soil conditions .

Until you get a local ground electrode out there I would be careful
bonding anything. It is best to drive 2 rods 6 feet or more apart.
That is about all you are going to get out of a rod electrode.
Rods are not really that good though. The best is probably a concrete
encased electrode, the rebar in your foundation. Next would be a
ground ring, a buried wire all the way around the building. Back in
the olden days we had the best electrode around when all of the
underground water pipe was metal and everyone had a metal to metal
connection all the way back to the water plant. There were cases where
the neutrals were totally gone and nobody noticed because they gut a
path through all of that water pipe back to somebody who had a good
neutral.