Potential of Radiators

[Richard7]

I have had problems in my house with hidden wire testers showing many areas are live when they are not. It is a new house and only 3 years old.

I wondered if it could be a problem with the heating system wiring.

My radiators are connected with plastic piping but when I use a voltmeter to compare them against the house wiring earth there is a small potential difference (only about 0.3V). Is this normal and because the radiators for some reason are at a different potential to earth and also, has anyone had the same issue with these hidden wire detectors.

Sorry to ask what may be very simple questions!

 

[bongos]

I have had problems in my house with hidden wire testers showing many areas are live when they are not. It is a new house and only 3 years old.

I wondered if it could be a problem with the heating system wiring.

What are the problems? Have you actually been getting "shocks"? Is your house protected by one or more RCD's?

My radiators are connected with plastic piping but when I use a voltmeter to compare them against the house wiring earth there is a small potential difference (only about 0.3V).

I shouldn't worry about a difference of 0.3v is that is all it is. Such a small value could be an inaccuracy in your tester or possibly capacitive coupling.

 

[ColJack]

how do you know they are not live? there might be a cable burried in the wall....

it also is likely that it's a combined detector that finds pipes and studs too...

 

[Richard7]

Thanks for the replies. I have tested my meter and think it is pretty accurate. Is it possible that just the fact that water is running through a raidator connected by plastic pipes might make it a slightly different potential to house earth.

Sorry to be dim but what is capacitive coupling?

I know the areas I have tested are not live as when I have drilled or gone behind the wall, there is nothing there.

 

[bongos]

how do you know they are not live? there might be a cable burried in the wall....

Aplogies. I'd assumed he meant tested with reference to the house earth.

 

[Richard7]

I did test them against house earth and this is what I am concerned about. The question about cable testers is I guess a separate issue but is what led me to test them in the first place.

 

[Richard7]

Does anyone know if it is common for radiators that are conncected by plastic pipes to be at a slightly different potential to house earth? Should I be worried? Thanks

 

[BS3036]

It's perfectly normal. If you connect one lead of your meter to earth and hold the other end in your hand you wil probably read a voltage. It's a capacitive coupling from all the live wires in your house.

To eliminate the effect, use either an old fashioned analog meter with no electronics in it, or do what voltage testers do and have a parallel resistor to sink the high impedance current.