In an earlier contribution to this discussion,
L Reid wrote:

"Set Square" wrote in message
...

The type of stat which you have *needs* 4 wires, and can't safely be
installed with 3. A common short-cut employed by some plumbers is to
use the green/yellow wire for the switched live (which you refer to
as the "call to heat"). This is unsafe for two reasons. Firstly the
stat needs to be eathed, but isn't when this is done. Secondly, a
wire which any reasonable person would expect to be earthed is, in
fact, live!

The RTS 1 is double insulated and does not need earthed.

L Reid

Fair enough, if you have a manual, and it *says* that. But the OP did say
that it had an earth terminal.

My old Danfos stat (which I've now replaced) sounds fairly similar from the
description, and had a notice inside saying "This device MUST be earthed" or
somesuch.
--
Cheers,
Set Square
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