Slight voltage on Shower head to switch ground

[TimHoward64]

I have a home owner who is an electrical engineer, This is new construction
He checked from shower head to the ground of the switch near the shower, Meter reads 2-4 volts
1 circuit in the house not in the bath room is turned off it goes away

Have traced lines between receptacles all good
cant see it ever touches the water line, which is plastic everywhere except at the shower valves to head , water heater(gas) and toilet stub outs
check a house down the street same thing, No one live there yet
all new construction single family 200 amp back to back service

 

[kwired]

I have a home owner who is an electrical engineer, This is new construction
He checked from shower head to the ground of the switch near the shower, Meter reads 2-4 volts
1 circuit in the house not in the bath room is turned off it goes away

Have traced lines between receptacles all good
cant see it ever touches the water line, which is plastic everywhere except at the shower valves to head , water heater(gas) and toilet stub outs
check a house down the street same thing, No one live there yet
all new construction single family 200 amp back to back service

What is supplied by that one circuit where the voltage goes away when turned off?

All new construction - does that mean water is non metallic lines for most of the installation?

 

[ptonsparky]

What kind of meter?

 

[GoldDigger]

Suspect conditions are:
1. Compromised neutral which is sending normal current through the EGC to GES, including water pipe, and pipe system resistance is causing the 2-4V offset.
2. Shower pipe is not properly bonded to GES and capacitive coupling in something connected to the other circuit is causing a phantom voltage. You (not he) should measure the voltage with a low input impedance meter.
3. Whatever other members suggest....

 

[jumper]

Suspect conditions are:
1. Compromised neutral which is sending normal current through the EGC to GES, including water pipe, and pipe system resistance is causing the 2-4V offset.
2. Shower pipe is not properly bonded to GES and capacitive coupling in something connected to the other circuit is causing a phantom voltage. You (not he) should measure the voltage with a low input impedance meter.
3. Whatever other members suggest....

My money is on #2.

 

[ActionDave]

Suspect conditions are:
1. Compromised neutral which is sending normal current through the EGC to GES, including water pipe, and pipe system resistance is causing the 2-4V offset.
2. Shower pipe is not properly bonded to GES and capacitive coupling in something connected to the other circuit is causing a phantom voltage. You (not he) should measure the voltage with a low input impedance meter.
3. Whatever other members suggest....

My money is on #2.

If it's not a metallic pipe system, and the OP indicates that it is, then the shower head would not be bonded and should not be bonded to the GES.

 

[jumper]

If it's not a metallic pipe system, and the OP indicates that it is, then the shower head would not be bonded and should not be bonded to the GES.

I was really going with the phantom voltage idea, what is causing it may be anyone’s guess.

2-4V? Prolly does not exist and EE got jumpy over nada.

Low impedance meter or an inline load would most likely solve this right quick. Shoot, you know this better then me.

 

[hbiss]

... water line, which is plastic everywhere except at the shower valves to head , water heater(gas) and toilet stub outs

You should have known right away. How is the voltage going to get there, through the water? This guy is an EE so they imagine everything (that he was going around measuring it to begin with proves my case). He's using a normal meter with a high impedance input. Phantom voltage. Probably would get some kind of reading just holding a probe with your fingers.

-Hal

 

[JFletcher]

Welcome to the forum

You should have known right away. How is the voltage going to get there, through the water? This guy is an EE so they imagine everything (that he was going around measuring it to begin with proves my case). He's using a normal meter with a high impedance input. Phantom voltage. Probably would get some kind of reading just holding a probe with your fingers.

-Hal

My money is on that as well.

 

[journeyman0217]

...makes me wonder if it was phantom voltage then why would the 2-4 volts go to 0 after he turns the breaker off?

 

[JFletcher]

...makes me wonder if it was phantom voltage then why would the 2-4 volts go to 0 after he turns the breaker off?

Hot wire of that circuit is no longer inducing a voltage on the switch ground.

 

[goldstar]

Had a situation like this several years ago and, like you, spent hours turning off breakers until we found the one causing the problem. However, we could not isolate the problem as most of the house was already sheet-rocked. As it turned out we found the triplex cable from the utility was rubbing up against the side of the house (aluminum siding). Once we corrected that the phantom voltage went away. I'm only telling you this because you shouldn't be looking for only obvious problems. Try to think "out of the box." It may end up being something wierd like in my situation.

 

[kwired]

Hot wire of that circuit is no longer inducing a voltage on the switch ground.

Or is no longer capacitively coupling to the water pipe.

Switch ground is hopefully at same potential either condition.

Add: if switch ground is not same potential either condition then it is open somewhere.

 

[gar]

180111-1149 EST

In this situation I want to talk about EGC and neutral, and not the word ground. At this point I don't think we are concerned with the the earth's potential.

At the main panel what is the voltage difference between the neutral and EGC bus bars?

The following are with a Fluke 27 with 10 megohm input impedance.

At the moment my main panel reads 0.9 millivolts between neutral and EGC. And 2.9 millivolts from neutral in the main to my supply copper water pipe about 4 feet away, but a longer grounding wire.

At my work bench EGC to neutral about 60 millivolts. A 50 ft extension cord EGC derived at the main panel to EGC at my work bench about 50 millivolts. Some of this voltage can be magnetically generated from the created 1 turn loop, high frequency RFI from fluorescents or LEDs, or current to EGC from noise filters in the fluorescents. Just call it residual.

In my kitchen 50 to 250 millivolts at different outlets fed from same subpanel with refrigerator and some lights on. Other loads may be changing. Sink to an EGC 50 millivolts. I have all copper water piping.

As a rough estimate without adding some large current load about anywhere my EGC to neutral at an outlet is less than 250 millivolts.

At a kitchen outlet (duplex) EGC to neutral changed from about 40 millivolts to 450 millivolts with the addition of a 10 A load in the other half of the duplex.

To the original post. We don't know the current, and we assume the voltage measurement was with a 10 meg meter. The next test that should be run is with the meter shunted with a 1000 ohm 1/2 W or 1/4 resistor. Now we have an ammeter with a sensitivity of 1 V per milliampere. The reason to do this is to protect the meter. Better than burning out the meter fuse (about $15) or damaging the meter. In the OP case the milliammeter range would probably have been OK, but in other situations you many not really know what the current could be. Half watt resistors are cheap.

.