Central Heating cables

[regsmyth]

Hello chaps,
While fiddling in the loft, noticed the cable from the tank stat to the ch terminal box has a chewed section, so I'll replace it.
But it's 2.5mm t+e with the earth snipped off at the ends.
Just want to check if it's ok to replace with 1mm2 t+e (presumably the load is tiny?), or should it be 1.5 since the supply to the FCU from the CU is also 1.5mm ( ie good practice or common sense issue?).
Thanks.

 

[Albert]

As a general rule, a bigger cable should not be a problem. The cable size selected is the one that can carry safely the load (+ de-rating factors) I think that if this cable is only to supply the control unit there is no reason why you can't use 1.5mm. But if it is to supply the heater it might be a load of 13A which I would use 2.5mm as minimum.

The fact that it is supplied (from the CU) using a 1.5mm, might be an important factor because it depends on the MCB/fuse rating. As I do not know the details of this installation I cannot comment, but to say that you should check the whole circuit, It might be that in the past an electrician or DIY person connected the thank to a lighting circuit... I am not saying that this is the case...but if it is it is not good!!![/list]

 

[regsmyth]

Thanks Albert
Yes perhaps before my time it supplied the immersion heater, but thats on a different circuit now.
All this cable does is take a live to the tank stat, and a switched live back to the ch terminal box. I don't know how much current actually flows through the tank stat and the room stat, presumably it's not a lot.
Anyway, cable now replaced with 1.5mm, so I'll puzzle over it no more.