Wiring help needed swapping over CH room thermostat

[Forty45]

I want to swap my old CH thermostat for a new one.

Photo of the old one and it's wiring diagram is attached - It is a Honeywell T6360B. I think that;
the Earth sleeved wire (on 1) is the Live,
Black (2) is N
and Red (3) call for heat.

The new one is a Drayton RTS2 (diagram also attached).
On that will;
N be the Black wire
L the sleeved Earth wire
and the Red wire go to 3?

 

[Mister Banks]

In theory you are correct but you shouldn’t be using the earth wire as a live, it’s against regs.

 

[muggles]

Yes that would work but using an Earth as a Live contravenes the Wiring Regulations and should not be done. Better to use a 2-wire stat, or a wireless one and re-wire at the other end.

EDIT, seems Mister Banks can type faster than me!

 

[Forty45]

Thank you both for explaining. Could it be the Regulations on using an Earth wire as Live have changed since the wire was installed (probably 40 years ago), or was it just wrongly done then?

 

[denso13]

or was it just wrongly done then?

It has always been wrong. Not rare though.

 

[RandomGrinch]

Thank you both for explaining. Could it be the Regulations on using an Earth wire as Live have changed since the wire was installed (probably 40 years ago), or was it just wrongly done then?

There is a slight distinction to be made in your case...

Before 2022, it was allowable, but inadvisable, to oversleeve the green/yellow wire in a multi core flex, to make it become a switched live.
If your wires were like this, it would be allowable to keep them - the wiring regs don't apply retrospectively, and changing a thermostat would unlikely qualify as an alteration of the wiring.

However, you have a twin and earth cable, the earth wire is bare copper without an extra layer of insulation.
It has never been allowable to use this type of wire as a switched live.

As has been said above, if you wish to utilise the existing cable, you could use a two wire (battery powered, or mechanical) stat and swap the wiring at the other end of the cable - ensuring the red and black wires become the live and switched live.