Hi Bud,
On 9/22/2013 9:53 PM, Don Y wrote:
A metal water service pipe (10 ft...) is still required to be part of
the earthing system. Not obvious you were saying water service pipe is
not to be used as part of the earthing system, but a lot of people think
that. An additional electrode is now required for new construction.
The latter. "Earth the plumbing" not "rely on the plumbing for earth".
The house I grew up in relied on water main for earth. And, the
water *meter* being metalic (I don't recollect a bonding strap
*across* the meter -- which was highly visible in the basement
workshop)
Here, I was stunned to see this same *apparent* practice (this house
being 30 years NEWER than my childhood home) as I could see the
clamp to the hose bibb located near the panel. On closer inspection,
however, I noticed another earthing conductor embedded in the
stucco heading off to a ground rod.
A stake (ground rod) is easy to install but is the worst of the commonly
used earthing electrodes. For new construction that has footings or
foundations a "concrete encased electrode" is required. It is a good
earthing electrode and a ground rod is not used.
I have overhead distribution, which is 8kV to distribution neutral
(13.8kV phase to phase). The 240/120V secondary neutral is bonded to the
transformer can and earthed at the pole.
That's what I'd remembered when I had overhead service. But, the below
grade service is covered by a large rectangular "box". One would think
the box itself would be earthed if just for safety.
Looking inside doesn't leave you with a nice warm feeling! Lots
of *big* conductors that are "exposed" (relying on the box to
cover them). Makes you wonder how good that bonding strap is
in the event of a car driving into it! :-/
[I was going to upgrade our service, here. Much of the EXPENSIVE
work can be done by the homeowner: trenching, installing plastic
conduit, shading, etc. But, the sight of those big conductors
left me squeamish: "Maybe we can just take this as an opportunity
to CONSERVE!" :> ]
It may be earthed at poles
without transformers. The secondary neutral could be interrupted, as the
hot wires are, where power is supplied by another transformer, but the
neutral is continuous. It has to be continuous because it is also used
as the distribution neutral, and it connects to the distribution neutral
where the 8kV is tapped of the 3-phase supply.
I expect underground would at least connect the secondary neutral to the
transformer can and earth them at the transformer.
In the US, a major function of the N-G bond required at the panel is to
carry fault current back to the transformer. If you have a H-G short,
the fault current takes the ground wire to the N-G bond at the service
and then the service neutral to the transformer. That results in a high
current to trip a breaker. With no N-G bond there would not be a
reliably high current.
(the half of that sentence unsaid is "... thereby allowing the hazard
to persist")
Sort of like designing a pinout for a power cable in a device such
that installing it backwards, *against* the mechanical keying's
wishes causes the power supply to see a short -- instead of
taking out the electronics.
My understanding is some of the UK does not have a "ground" wire in the
utility supply and the building ground is just earthed at the building.
And a RCD main in the UK is to provide a trip in the absence of the high
current above.
No doubt a way of dealing with grandfathering?
Most, if not all, of the exceptions were removed maybe 5 years ago.
Some were silly (e.g., tying the panel to neutral given that
neutral was bonded to earth *at* the panel).
There are a couple changes in the US code that make a common neutral
("multiwire branch circuit") less common.
One is that the supply breaker must now simultaneously disconnect all
the circuits associated with the neutral. (It does not have to be a
common-trip, a listed handle tie can be used.)
I'm not fond of handle tie's (though realize they are an economical
way of doing things) as they are too easily severed. When we moved
in, here, I immediately noticed the tie for the 220V cooler was
split. Someone seeking to be able to turn off the *furnace*
blower (that shared the circuit) while leaving *half* the cooler
circuit live??
:-(
In a business it can be a
real disadvantage to turn off 2 or 3 circuits to work on only one of them.
The other is that in a house most of the circuits now have to be (new
construction) AFCI protected. Like a GFCI breaker, AFCIs require a
separate neutral that goes through the breaker. You could use a 2-pole
breaker but they are expensive. AFCI receptacles are now available, but
in general you can't use them as an alternative to a breaker like you
can with a GFCI receptacle.
Ah, I didn't realize AFCI's were now Code requirements. Bedrooms?
IMHO it is the most confusing of the commonly used chapters.
Problem with all building codes is they are written requiring
a "language lawyer" for proper interpretation. This, IMO, is
counterproductive (code wars, etc.). The code should go to
great pains to explain what it's intent is so folks don't
have to reconcile "conflicting" sections. It's purpose is to
make things *safer*. Imagine if "STOP" signs said,
"GRADUALLY DECELERATE UNTIL FORWARD MOTION HAS BEEN HALTED
FOR A PERIOD SUFFICIENT TO ENSURE ALL FORWARD MOMENTUM HAS BEEN
ABSORBED" (WTF?)
I can recall looking for clarification for a code section that
implied the need for a "divided Jbox" (other than mixing line
and low voltage conductors in the same box). I was never
able to find anyone who could clarify the requirement and
ended up just using *two* Jboxes (instead of drawing attention
to a single *divided* box)
<frown>