todd wrote:
"chuck" wrote in message
ink.net...

Hello Todd,

From the way you've posed the question, I can't tell whether you
understand the basic electrical concepts involved.


You'll have to bear with me. I'm just a stupid mechanical engineer.


Let me just say that appliance ground faults are so common that a good
part of the National Electrical Code (NEC) is devoted to protecting people
from them. Breaking the ground connection exposes one to the very dangers
that the ground connection was installed to protect against.


So what you're saying is that there could be an existing ground fault that
is currently being sent to ground through the water pipe? I take that to
mean that the ground, and thus the copper pipe it's bonded to, is energized.



Todd, I think we're probably using different terminology. But yes, I'd
be willing to agree the copper pipe is energized, in the sense that the
assumed ground fault current is flowing through it.

In the eye of the NEC, there is a connection at the service entrance
between the green grounding wire and the white neutral and ground. An
appliance ground fault current SHOULD flow through the green grounding
conductor to the service entrance, and from there, take the path of
least resistance through that neutral wire back to the transformer on
the pole. Of course the higher resistance path through the ground is in
parallel with the neutral wire, so you get some current through the
ground as well. It is normally not a good thing for there to be a lot of
current through the ground, and its presence could indicate a problem
with the neutral connection, etc.

Taking a shower is just not equivalent to removing the protection against
appliance ground faults that the NEC requires.


I'm not sure if you're referring to removing the protection permanently or
long enough to put a proper clamp back on. I assumed the OP was talking
about removing the ground connection just long enough to get it attached
back to the pipe with a clamp.

Yes, the latter is what I assumed also.

My assertion was that if there was enough
voltage present in the ground wire to kill you, that you probably had other
worries in addition.

Agreed. Except that there is no voltage to speak of on the ground wire
while it is connected to the copper pipe (i.e., to ground). There is a
current through the wire. When the connection to the pipe is broken, at
that time a voltage is present between the pipe and the wire. Placing
yourself across that voltage is what could be hazardous.

If that was the case, I wouldn't handle anything
connected to the plumbing fixtures until the situation was corrected.

Well, touching the plumbing fixtures should be safe because they are
essentially at ground potential, again due to the copper pipe
connection. That is a benefit of the grounding system. But if currents
are detected in the grounding wire, something is amiss and maybe should
be corrected.


Perhaps I'm wrong. Most of my work-related electrical experience was in a
slightly higher range of 15-500kV when I designed insulators for
distribution, sub-transmission, and transmission lines where the electrical
problems encountered were somewhat different.


Fascinating. I'd be lost in that area.

By the way, for the OP, one thing I haven't seen mentioned is that, at least
around here, the ground is connected to the water line on just this side of
the meter. Then, another ground wire bridges the meter so that the ground
would still be in place in case the meter was removed.


The reason for that jumper is more likely that the meter itself does not
represent a good, low-resistance path. You see those jumpers around
plastic-bodied filters also. In the past, service entrance grounds were
often connected to metal plumbing systems. In many cases these systems
were "upgraded" to plastic, and the residence was left without any
ground connection at all!

FWIW, with so much PVC in use in new construction, the NEC now requires
a dedicated ground rod or two at the service entrance.



todd



Chuck