I appear to have an electrical bonding problem with my plumbing. I am
measuring 60VAC between my kitchen faucet and the kitchen drain fitter. The
problem became evident when I replaced the old PVC drain trap with a shiny,
new metal trap. Goodbye, insulator. Hello, tingle.
Further investigation reveals that the kitchen sewer drop is not bonded to
the water pipes and/or the service ground. The main sewer drop (other side
of the house) is bonded to the water supply pipes. The supply pipes are also
bonded to the service ground at that point.
The simplest solution seems to be to run a short bonding cable between the
kitchen drain line and the nearby supply pipes. I can do this in the
basement underneath the kitchen. Would this be satisfactory? I don't want to
create a ground loop. Perhaps I should run a longer bonding cable from the
kitchen drain line to the point where the service ground connects to the
supply lines? Or is there some other approach I should take (aside from "pay
an electrician to do it?)
60 volts indicates a serious problem. Usually a difference in ground
potential is 2 - 5 volts. You had better call an electrician now.
I'm thinking that there is a problem with your neutral conductor and that
you don't have a very good ground for your service. Another possibility is
that one of your neighbors has a problem with their neutral and the current
is coming through your pipes.
Is there a garbage disposal unit in this sink? It may be defective.
Aside from that, you have a serious and potentially dangerous
situation there and I'd recommend (even though you don't want to) an
electrican look at it.
You are taking a very real risk that either someone will be injured,
or you will create a fire hazard if there is an inner wall short
between wiring and the plumbing.
No. However, I installed a dishwasher several months ago.
But I changed the drain trap from plastic to metal at the same time,
which bonded the drain fitter to the drain line and allowed me to
discover the problem. So the problem may have been there for some
time and gone unnoticed. I did shut off the dishwasher circuit, and it
had no affect on the problem.
I'm going to try shutting off circuits one at a time, and see if I can
isolate the cause. Failing that, I guess I will need to hire a professional.
I did some troubleshooting and found the source of the voltage (actually
not 60). Somebody (not me) installed an outlet in the upstairs bedroom and
spliced it into an existing knob-and-tube circuit. Then they grounded the
the kitchen vent stack in the attic. I removed the ground wire, and that
the stray voltage in the kitchen. So now my outlet is a two-conductor
(like most of the outlets in the house, on the old KT circuits.) The outlet
to work fine.
But I really don't understand why there would be voltage coming off of the
on the outlet box. Should I be looking for a fault in the outlet?
I think it happend because knob and tube wiring does not have a ground, the
3rd wire most newer wiring has, and grounding it to the vent stack was not a
good idea, used to ground them to a cold water pipe, back when most water
pipe were galvenized pipes, ran underground from the city main, it made a
pretty good ground, now days there is a ground rod installed near the
And in most breaker boxes, netural and ground go to the same place, least
the last time I looked inside one, I think on newer ones there is a seperate
ground term strip, grounding it to the vent stack, gave it a netural
potential there and your tingle, thats why kitchens and baths are supposed
to have GFCI's either outlet or breakers.
Hope this answers some questions.
Agreed. I suppose the vent stack _might_ have been an acceptable ground,
had the vent stack itself been bonded to the service ground. But it wasn't.
And the kitchen sewer line has been replaced with PVC, so the vent stack
(1-1/2" galvanized) doesn't even have its own path to earth.
But where is this voltage coming from? It is load-dependant; if nothing is
plugged into the offending outlet, then I measure zero VAC between the
kitchen faucet and the kitchen drain pipe. The measured voltage varies
as I increase the load on the outlet. (These tests were performed with
the vent stack ground wire reconnected, of course.) Does this indicate
a fault in the outlet? Or is it normal to have 40-60VAC present on an
outlet ground when a load is placed on the outlet?
With K & T anything is possible. It's best not to try and tap off of it for
expansion, but it's too late for that. Take a look inside of the outlet box
and see if any conductors have the insulation scraped off and might be
touching the metal.
In the outlet, or anything that was plugged into the outlet. Under
normal conditions, there isn't supposed to be any electricity going
into the ground. Something isn't right, there. Also, make sure the
neutral for that outlet is groud potential. If it has significant
voltage on it, it's probably time to call the electrician.
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