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Posted by Tom Horne, Electrician on December 21, 2006, 11:40 am
J wrote:
> I've read a number of newsgroup postings and there is so much
> disagreement it is hard to get a straight answer. So don't give me
> the 'asked&answered' response - just save your breath. I might be
> flogging a dead horse but here we go....
>
> My house was build in the 50's and all of the original outlets were
> two prong with no grounds. At some point in the last 50 years,
> before I moved in, someone upgraded the service with a 100 amp panel
> and added some more outlets which are grounded. I believe there are
> no grounding rods, only the cold water pipe is being used as the
> grounding electrode. This is one part that has lots of disagreement
> but I'm guessing this was up to code when the work was done. Also,
> this is not really where my question lies. The gas line is also
> bonded to the cold water pipe and sewer stack in the basement and
> there is a jumper over the water meter.
>
> I'm thinking of adding a subpanel in the detached garage. It would
> be a fed through #10 THWN (4 wires) from a 30 amp breaker through
> existing 1/2" EMT. Can is use RW90 in Canada? Since it's a seperate
> building I would need to drive a grounding rod at the subpanel to
> comply with the code. Can you explain why this is necessary? If
> it's the same building then it is not necessary, right? The neutral
> and ground at the subpanel would not be bonded. That part makes
> sense to me. Also, would the gas line in the garage need to be
> bonded to the ground there? This would seem appropriate to me, but
> maybe not necessary. For now the ooooold heater chassis is not
> grounded.
>
> Thanks for your time,
J
The answers I'm about to give are based on what I believe to be good
practice but I have no knowledge of the Canadian Electric Code. The
bonding arrangement you describe in your home would be perfectly normal
under the US National Electric Code.
In general the Equipment Grounding Conductor of the circuit that is the
likely source of the power to energize the gas line is considered
sufficient bonding of the gas line under US codes. There is no harm in
installing a separate bonding conductor to the gas line and that may be
required if there is no electric circuit, which includes an Equipment
Grounding Conductor, to the gas heater.
The reason that you should construct a Grounding Electrode System at the
separate building is to reduce the likelihood of damage from lightning
or a power cross to the supply wiring.
You said you would be using an existing EMT raceway to run your wiring
so you won't be doing new trenching. That means that to build a better
Grounding Electrode System than the minimum two driven rods you would
have to excavate for that purpose. If your just using the garage to
store and service vehicles that would not be warranted. If you have
other uses in mind for the garage please say so.
--
Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison
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