John Grabowski wrote:

"HorneTD" wrote in message
ink.net...

John Grabowski wrote:

"the_tool_man" wrote in message
egroups.com...


Hi all:

Six years ago, I built my workshop about 150ft from the house with a
100A service. I ran a four-conductor cable to the subpanel in the
shop, and kept the ground and neutral conductors isolated from each
other. I did not bond the sub-panel ground to its own ground rod,
thinking it might cause a ground loop and/or noise in the intercom
circuit bewteen the buildings. More recently, when I put in a spa with
it's own GFCI breaker, I had several people advise me to drive a
separate ground rod for it, and that I should have done the same for my
workshop. So far, I have had no issues, but I want to make sure I did
the right thing.

My searches here have yielded many debates on the need to keep the
ground and neutral bonded only in the main panel and not the subs
(which is how I did it), but nothing about the ground rod question.
Does a remote subpanel need its own ground rod or not?
Thanks in advance,
John.


Since you ran a grounding conductor with the feed to the subpanel, you

do

not need to install a ground rod at that location.

If you feel the need to install a ground rod it should be at the main

panel.

What is your current main ground?


John Grabowski
http://www.mrelectrician.tv

Sorry John but that is bad information.

Every building that has more than a branch circuit to supply it has to
have a grounding electrode system. That can be as little as a single
ground rod if it has an impedance to ground of twenty five ohms or less.
If the impedance of the single rod is higher you have to add a second
rod. Most electricians do not bother to measure it and just add a
second rod. If the building already has an electrode such as a concrete
encased electrode then you only have to bond the service equipment
enclosure to it and your done. In all cases each separate building gets
a grounding electrode system. There are no exceptions under the US NEC.
The objective is to "limit the voltage imposed by lightning, line
surges, or unintentional contact with higher-voltage lines" and
"stabilize the voltage to earth during normal operation."

250.50 Grounding Electrode System.
If available on the premises at each building or structure served, each
item in 250.52(A)(1) through (A)(6) shall be bonded together to form the
grounding electrode system. Where none of these electrodes are
available, one or more of the electrodes specified in 250.52(A)(4)
through (A)(7) shall be installed and used. Copyright 2002 National
Fire Protection Association.

In short every building
1) needs a grounding electrode system if it is supplied with more than a
branch circuit.
2)The building disconnecting means gets bonded to the grounding
electrode system.
--
Tom H
Tom, I agree that each building needs to be connected to the grounding
electrode system. However my interpretation is that the grounding electrode
system originates at the main service entrance and can be extended to
secondary buildings along with the power. Therefore a ground rod at each
secondary building is not necessary as long as the building components
(Metal piping, steel, subpanel, etc.) are bonded to the grounding electrode
system that originates from the main service.

I seem to recall an article from a few years ago in one of the trade
magazines that discussed this issue of multiple grounding along a
distribution system. I think one of the problems is that it is possible
that the ground rod in a secondary building could have less resistance than
the primary ground rod (Or water pipe). Since electricity follows the path
of least resistance it is possible that the loss of a neutral could have
current travel away from the main service to a secondary building's ground
rod. Anyway, my memory isn't that great. I could be mistaken.

John G.

John
We can talk what ifs until the cows come home. The requirement in the
US NEC is plain. If the building is supplied by a feeder rather than by
a branch circuit it must have a grounding electrode system and the
building disconnecting means must be bonded to it. It makes no
difference whether there is or is not an Equipment Grounding conductor
run with the feeder a grounding electrode system is still required at
each building. Which conductor of the feeder gets bonded to the
Grounding Electrode System at each building is dependent on whether
there is an EGC in the feeder. Either way you must bond the building
disconnecting means to a grounding electrode at the building that the
building disconnecting means serves. The US NEC does not allow any
other course of action.
--
Tom H