On 15/05/2016 10:30, wrote:
On Sunday, 15 May 2016 01:06:28 UTC+1, Fredxxx wrote:
Its only a short distance. I would have preferred to have exported an
earth as well, given the cases are metal, and the transformer of unknown
origin.
I was looking for shielded cable or screened twisted pair, then it
dawned on me I can make one conductor earth as well as 0V return!

Fire alarm cables are usually red, I don't know if the door closer wiring has to be too, but I don't think it would do any harm.

https://www.tlc-direct.co.uk/Products/NB1slash2R.html

Screened, available in 2+E and 4+E. Sold per metre.

Given the solenoid is fail safe, and power disconnected on alarm, I
don't feel the need to use fire resistance cable. However it would be
smart to make it easily distinguishable from other cabling.