hugh ] wrote:

I have the same problem - no neutral as the original thermostat was
simple on/off. However the new thermostat is double insulated and
doesn't need an earth, according to the manufacturer. The earth terminal
is there purely for convenience to park an earth wire, if it is present.
So provided I am sure this earth is isolated from all others and I put
blue tape on each end can I use it to feed a neutral to the new stat?

No.
What if the cable is cut half way along in the future? Blue and
Brown/Red and black will both be live, and copper will be neutral.
Also, no insulation on the ends. Far too easy to get it wrong in the
future when you have gone.
Someone drills through the cable - it wont trip as there is no earth
there, so they'll be buzzing away, using your electric to fry, and
hopefully pass enough current through themselves to trip the fuse/CB
through an overload.

But people do things like this all the time, as it is your house, do
whatever you want.

Alan.

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