At 07:14 AM 1/5/2007, Roger Kissel wrote:
>John
>
>While I agree with you on grounding to a water pipe (and main) and I
>acknowledge the fact that you are a licensed electrician, there is
>one thing that bothers me about your statement. Maybe the code is
>(currently) wrong but the fact that you have not mentioned something
>else bothers me.
>
>You said: a second panel ground should run to the water main and
>terminate on the street side of the valve.
><snip>
The increasing use of plastic pipe is probably why a lot of
jurisdictions have a local code requirement for using only a
Concreted Encased Grounding Electrode (a Ufer ground). For new
construction, particularly, it's pretty easy to just lay 20 ft of
wire in the foundation footing, and it gives a better quality (as in
lower R and longer life) ground than rods, pipes, etc..
The code (NEC) still allows other forms of ground, but that's
probably for legacy. There's also a whole can of worms when doing
modifications. At what point does a jurisdiction require updating to
the latest code. Lots of houses were wired with 2 pole ungrounded
outlets and they still exist. Typically, there's no requirement to
go in and retrofit unless serious remodeling or changes are done.
>ny6dx wrote:
>
>By code the outside panel ground should be in direct contact to earth and
>terminated at ground rod. a second panel ground should run to the
>water main and
>terminate on the street side of the valve. This is in case you lose
>the nuetral
>from the pole you do not send 220 volts throughout the house.
>P.S.
>I am a licensed electrician if that matters.
I would assume that you'd have bonded the neutral and ground at the
service entrance? So, if the neutral failed on the drop (which
happens fairly often, surprisingly), you will get voltage
fluctuations on the two legs, but unless the distribution transformer
mid point were also grounded, there'd be no current flow through the
grounding system.
One part of the electrical safey ground, anyway, is so that grounded
(green wire) cases are at the same potential as the floor the user is
standing on. The grounded neutral is a hold over from days of yore
when the chassis was connected to neutral, and you'd want to keep
chassis at close to earth potential (for the same safety reason). I
suppose that for light sockets, that reason still applies, as you
unscrew the bulb, the exposed metal is connected to neutral, not hot.
For most appliances and utilization equipment these days, both hot
and neutral are isolated from the chassis (and certainly from
anything the user might touch) so "grounded neutral" is probably less
of an issue.
My officemate (WB6CIA) had the neutral fail (at the transformer), so
it created an interesting situation where he and his neighbors
interacted. He could turn on a big (110V) load, and not only would
some of his lights brighten and others dim, but so would his
neighbor's. It's unclear whether the two house's neutrals were
interconnected still at the pole, or whether the ground carried the
differential current. I think the former.
As far as bridging around water meters goes, I have read that this
was done to eliminate the possibility of galvanic currents flowing
through the body of the meter (which would typically be brass or
bronze) and corroding the differential metal pipe joints. This would
be especially true if the main were iron and the service pipe being
copper, or something like that. Might also have been for safety for
the plumber, if there were stray electrical current flowing because
the pipe was used as the grounding electrode in a high resistivity
soil situation. Who knows what might be the case in old wiring
systems. In Manhattan, there's places where significant ground
current flows because of Edison era wiring practices (running just
one wire under the sidewalk in an iron pipe, and the return being at
the other end of the block). Dogs get killed, homeless people get
shocked when urinating on the street, etc. There's no documentation
of where the wires are, so they basically have to wait til something fails.
Jim, W6RMK
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