redundant thermostat

[telecoms]

In my hall on the wall is left a old room thermostat,it was used when there wa a oil fired boiler in the house,the boiler was replaced for a gas one and a new thermostat placed on the landing,(all before i owned the house),now i`m decorating the hall,when i put my fluke on the positive(red) cable and put the other probe to earth a get a measure of 26v ac,anyone got an idea why and where from ?

 

[breezer]

induction?

 

[telecoms]

not sure where it was fed from originally,i`ve had consumer unit changed and tested electrics,where would it get 26v induced from seems quite high,i want to get rid of it really,would it be safe to tape up and bury in wall ?

 

[Space cat]

when i put my fluke on the positive(red) cable and put the other probe to earth a get a measure of 26v ac,anyone got an idea why and where from ?

The hidden capacitor strikes again!

That wire must be running side by side with one or more live cables. The capacitor is formed by the cores of the cables and the space between them. When you put your very high input impedance meter between the dead cable and earth a tiny current flows across the capacitor, along the wire and through your meter to earth. There's a thread on capacitors further down this forum.

I would guess that the other end of that cable has been left dangling somewhere. Places to look would be where the old boiler or programmer used to be. This is a bit of a problem since it was removed before you got there but if it was mine I'd go looking. A wire has two ends and I hate not knowing where one of them is! When you've found both ends, either take the whole length out or, if this is not feasible, short all the cores together at each end, tape them up and bury them.