Wire colours for central heating controls

[DavidM]

I am planning to update my CH controls to improve efficiency (cylinder thermostat, programmeable room thermostat etc). If I connect say the cylinder thermostat with 3 (live, neutral, switched output) core cable (not TW&E) is it permissable to use the green/yellow core for the switched live return from the stat to the control block? If not how should I wire it (it's about 3 metres from the stat to the control block near the boiler)? Are there any general rules/guidelines to follow re colour coding or cable types when interconnecting all the components on a CH system? Thanks, David.

[Andrew Gabriel]

No. The reason being that the cable must have an earth in it connected to the supply earth even if there's no earth connection at the thermostat (which seems unlikely in any case). Given this, you'll be using the green/yellow core as the earth as it makes no sense to use anything else.

You can buy 4 and 5-core wire for such applications. B&Q used to sell it by the metre, but I think you have to buy a pre-cut length (or a whole drum) now. You might find it at a good electrical shop by the metre.

Not really. Stick as near to the correct colours as possible, and sleeve any live conductors with red or brown sleeving if they are some other colour.

[dave stanton]

Please please don't. But if you must PLEASE mark it with a red sleeve or even red tape. I have just spent an hour at a friends house working out what exactly some plumber was doing with the earth wire (NO it was not earth) on the thermostat wiring.

Dave

[Dave Plowman (News)]

You mean flex, rather than cable? Sleeve the entire green/yellow where exposed with red sleeving.

[raden]

In message , Andrew Gabriel writes

The last roll of 5 core cable I bought, I got from Plumbcenter, I did have to order it in advance though

[raden]

My brother-in-law's timer uses the earth for switched live (but that's in Belgium)