Electrical question - power still present in line, even with power switched off?

[Jeff7]

Got a 240V line here, it's switched off at the thermostat and at the breaker. There is still 5.22V at 20uA reading from the ground, to either hot or neutral. There's 0 between hot and neutral. What causes this? I'm guessing that the voltage is excess charge in the ground, just getting picked up by the voltmeter.

 

[Iron Woode]

you have a bad ground. You should be getting Zero volts with power off.

 

[Kenazo]

put your tongue across those leads.

 

[EyeMWing]

Bad ground. Reground it.

 

[Jeff7]

Originally posted by: Iron Woode
you have a bad ground. You should be getting Zero volts with power off.

I think that a concrete basement floor is a good ground...I just gave that a shot instead of the ground wire. I put the one voltmeter lead on the floor, and the other on the black wire. 5.1V. Same with the white wire.

 

[EyeMWing]

Originally posted by: Jeff7

Originally posted by: Iron Woode
you have a bad ground. You should be getting Zero volts with power off.

I think that a concrete floor is a good ground...I just gave that a shot instead of the ground wire. I put the one voltmeter lead on the floor, and the other on the black wire. 5.1V. Same with the white wire.

Uh, I think concrete is an insulator. Try a drainage pipe or somthing.

 

[Jeff7]

Originally posted by: EyeMWing

Originally posted by: Jeff7

Originally posted by: Iron Woode
you have a bad ground. You should be getting Zero volts with power off.

I think that a concrete floor is a good ground...I just gave that a shot instead of the ground wire. I put the one voltmeter lead on the floor, and the other on the black wire. 5.1V. Same with the white wire.

Uh, I think concrete is an insulator. Try a drainage pipe or somthing.

I thought so too. Try touching an ungrounded computer case while standing barefoot on a concrete floor - make sure that the hot and neutrals aren't reversed first though. You'll probably get a mild shock. Then put shoes on. No shock. I've done that already. We did get the wiring redone then though.

 

[HomeBrewerDude]

you get this on all your circuits?

 

[Iron Woode]

Originally posted by: Jeff7

Originally posted by: EyeMWing

Originally posted by: Jeff7

Originally posted by: Iron Woode
you have a bad ground. You should be getting Zero volts with power off.

I think that a concrete floor is a good ground...I just gave that a shot instead of the ground wire. I put the one voltmeter lead on the floor, and the other on the black wire. 5.1V. Same with the white wire.

Uh, I think concrete is an insulator. Try a drainage pipe or somthing.

I thought so too. Try touching an ungrounded computer case while standing barefoot on a concrete floor - make sure that the hot and neutrals aren't reversed first though. You'll probably get a mild shock. Then put shoes on. No shock. I've done that already. We did get the wiring redone then though.

In a house all ground should be tied (figuratively speaking) to the cold water line.

 

[OZEE]

Most likely, your Neutral is not bonded to ground. Get an electrician out there to check the neutral bonding.

 

[Jeff7]

Everything should be good with the power. We had some new circuits added a few years ago, and the guy also checked a lot of the existing circuits, which had open grounds, and some hot/neutral reversals. We've got one of those little 3-light circuit testers, and it shows everything's good here, except for this 240V line, which of course would blow out the tester.

Just did a test on a live, correctly wired 120V outlet. Neutral to ground (concrete or the ground plug) gives 0V. Hot to ground gives ~21V. And of course, hot to neutral gives 120V.

 

[DrPizza]

That's bizarre.. but you mentioned a thermostat...
Where exactly are you taking these readings...
And, I'll toss out this suggestion (since everything else reads 0 to the ground)

Perhaps there's a battery somewhere and there's some leakage to the circuit you're testing? ie. do you have a programable thermostat that has a battery in it?

 

[Thegonagle]

Originally posted by: Iron Woode
In a house all ground should be tied (figuratively speaking) to the cold water line.

More specifically, it should be clamped to the cold water pipe upstream from the water meter. If the ground is not clamped to a pipe upstream from the meter, the meter should be jumped from one side to the other with a short length of cable.

 

[AlienCraft]

Connections need to be re-made from time to time, especially if dealing with a connection with dissimilar metals. Given that it is highly unlikely that any two manufacturers have the exact same alloy in a connector, there is bound to be some electrolysis happening. Combine that with any vibration or heating / cooling contraction and you can see why there may be a degradation over time.
A concrete floor is only a ground if you are connected to the rebar in an approved manner.
Ground Rod connection and Water / Gas Pipe bonding are very important , for safety reasons.
You should consult your local Building Permit / Code Enforcement Agency for details regarding this aspect in your area.