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Homeowner Forum / Construction / May 2008Residential plumbing bonding question
Good morning. 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?) Thanks -Mark > Good morning. > [quoted text clipped - 18 lines] > Thanks > -Mark 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. >Good morning. > [quoted text clipped - 18 lines] >Thanks >-Mark 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. > Is there a garbage disposal unit in this sink? It may be defective. 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. *sigh* > 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. I did some troubleshooting and found the source of the voltage (actually 40VAC, 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 box to the kitchen vent stack in the attic. I removed the ground wire, and that eliminated the stray voltage in the kitchen. So now my outlet is a two-conductor ungrounded (like most of the outlets in the house, on the old KT circuits.) The outlet appears to work fine. But I really don't understand why there would be voltage coming off of the ground on the outlet box. Should I be looking for a fault in the outlet? Thanks -Mark 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 serivice main. 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. C >> I appear to have an electrical bonding problem with my plumbing. I am >> measuring 60VAC between my kitchen faucet and the kitchen drain fitter. [quoted text clipped - 20 lines] > Thanks > -Mark >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 >serivice main. 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? Thanks -Mark >>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 [quoted text clipped - 19 lines] > Thanks > -Mark 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. > 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. I think you're right. I'm guessing that the neutral wire is contacting the box. We'll see. Thanks for all your help. -Mark >But I really don't understand why there would be voltage coming off of the >ground >on the outlet box. Should I be looking for a fault in the outlet? 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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