mild shock from plumbing

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  #1  
Old 05-08-04, 11:31 AM
xxDave
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Unhappy mild shock from plumbing

My inlaws just moved into a new house. When you're in the shower and you go to turn off the water, you get a mild shock. Would this indicate a problem with the ground on the electrical panel? Or would it indicate a fixture wired incorrectly or possibly a partial short was caused when the sheetrock was put up? Thanks.
 
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Old 05-08-04, 06:35 PM
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I could mean both. If they have a electric water heater the elements could be leaking to the water system.
 
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Old 05-08-04, 06:44 PM
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This is a problem that needs to be investigated, and most probably fixed immediately.

A surprisingly small current can kill someone, if it happens to cross the heart in just the right (wrong!!!) way. This same current flow would simply produce a mild sensation if it goes through limbs only.

If the plumbing is entirely plastic, it may be that the mild shock is caused by static electricity build up. In which case the problem probably doesn't need fixing.

If the plumbing is metal, then the shock indicates some sort of grounding error.

All of the metal pipes in the bathroom should be electrically bonded together, to prevent voltages between metal pipes. I would check for the following:
1) proper bonding between the electrical system and the metal water pipes, 2) proper bonding jumpers on the metal water pipes at any insulating fitting and possible break (eg across any 'dielectric unions', across the water meter, and across the hot water heater),
3) proper bonding to metallic drain piping.

Electrical bonding means having a suitably sized wire (size depends upon your service) connecting all of these piping systems together so that they are at the same voltage, so that you cannot get a shock between any of these pipes.

Finally, because this is a 'minor' shock, I would investigate for a 'neutral to ground' fault. This is a short circuit between the _white_ wire and ground. There are no big sparks, and the circuit will continue to function normally. What happens is that some fraction of the circuit current will flow through the ground conductor system, and through anything (including a person) which is part of the ground.

-Jon
 
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Old 05-09-04, 03:12 PM
WFO
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Can you read an actual voltage between the fixture and ground? If so, try cutting off your main breaker and see if the voltage goes away. If it doesn't, the problem may not even be on your system.
We have extremely sandy soil in our area that makes a really poor ground during the summer when it's dry. We've had several cases where a malfunctioning water well will put a current into the water table that shows up on a neighbors' plumbing as much as a quarter of a mile away.

Our linemen will go to neighboring houses to check for the same problem. If they find it, they continue in whichever direction gives them increasing voltage readings. When they find a spot where it quits increasing, they start turning off wells. Bingo! Voltage disappears!
Try all the other stuff first. Your utility may not be as cooperative as ours.
 
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Old 05-20-04, 09:25 AM
xxDave
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Thanks for the replies. The plumbing is metal. We were actually able to read voltage on the ground line which was traced back to a specific breaker. There were 3 wall sockets on this breaker. We pulled them out of the wall and didn't see any issues. However, just doing this reduced the voltage measurement. Starting at the far end, we disconnected the first socket from the second. This eliminated the voltage. We still don't see any nicks or cuts on any of the wires, so the issue may be just behind the socket box. For now we are just going to leave that socket disconnected.
 
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Old 05-20-04, 01:52 PM
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I am glad that you were able to solve the immediate problem. I would still recommend that you double check the 'bonding' between your plumbing and the grounding system, and check the quality of your ground system connections. I am not sure what you mean by "We were actually able to read voltage on the ground line which was traced back to a specific breaker.", was this voltage between the ground wire and the pipe, or from the ground wire and some other ground electrode?

In any case, if you measured voltage between your water pipes and your ground electrode, then this means that your water pipes have not been properly bonded to your ground electrode. You will need to install a suitably sized wire between the various pipes and your ground wire, to make certain that they are at the same potential and that there is no shock hazard between them.

-Jon
 
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Old 05-24-04, 11:41 AM
xxDave
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We disconnected the ground from the main box and measured a voltage between the the ground electrode and the ground wire to the box. We then shut off breakers one at a time until we determined which one was causing the voltage.

We didn't measure a voltage on the water pipes. I don't see a specific ground to the water pipes, but I assume this exists somewhere since I expect that was the path causing the mild shock. We do plan to add our own ground.

Thx
 
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Old 05-24-04, 04:41 PM
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No ground bond to the water pipes could be part of the problem. This bond makes sure the pipes are at ground potential.
 
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