Confused by room thermostat wiring

DominicH

I bought an electronic thermostat to replace my traditional mechanical one (installed ca. 1980). Removing the cover from the old one, I was expecting to see live/neutral/earth etc., perhaps in the old colour scheme. Instead, the old thermostat is wired with red, yellow and blue cables, which the internet tells me is probably three-phase wiring? At this point, I start to feel a little out of my depth. The new thermostat just has a modern style two-wire connection arrangement. I was expecting to have to make safe a neutral and earth wire and then connect up the live wires, but I am not sure what to do with these red/yellow/blue wires. Any tips? (I know, I know, get a professional to do it).

victor2

DominicH wrote: »

I bought an electronic thermostat to replace my traditional mechanical one (installed ca. 1980). Removing the cover from the old one, I was expecting to see live/neutral/earth etc., perhaps in the old colour scheme. Instead, the old thermostat is wired with red, yellow and blue cables, which the internet tells me is probably three-phase wiring? At this point, I start to feel a little out of my depth. The new thermostat just has a modern style two-wire connection arrangement. I was expecting to have to make safe a neutral and earth wire and then connect up the live wires, but I am not sure what to do with these red/yellow/blue wires. Any tips? (I know, I know, get a professional to do it).

Your last bit is right.
It's got nothing to do with 3 phase wiring. One of the three wires may just be an earth, so it is only the other two you need to connect to your new thermostat, unless it has a metal case.
If you really want to do it yourself, you'll need to identify where the wires go into at the other end, which may well be a separate control unit for your boiler. From that you can establish what they are and what sort of voltage they carry.

muckybutt

Oh dear ! 3 phase wiring lol.

Its blatently obvious you have no idea what you are doing, if you had the slightest idea of what you were doing then I would have advised what to do, but in your case......get a sparky in for your own safety.

moonrakerz

muckybutt wrote: »

Oh dear ! 3 phase wiring lol.

..........415V one assumes !!

mikey72

victor2 wrote: »

Your last bit is right.
It's got nothing to do with 3 phase wiring. One of the three wires may just be an earth, so it is only the other two you need to connect to your new thermostat, unless it has a metal case.
If you really want to do it yourself, you'll need to identify where the wires go into at the other end, which may well be a separate control unit for your boiler. From that you can establish what they are and what sort of voltage they carry.

Probably very unlikely to be earth.

victor2

mikey72 wrote: »

Probably very unlikely to be earth.

Well, somewhere between 415V and earth - probably.

ziggyman99

Use the red and yellow, isolate the blue.

DVardysShadow

ziggyman99 wrote: »

Use the red and yellow, isolate the blue.

Works for the National Lottery, so there is a chance it will work for wiring.

The correct way to approach this is to work out what function each wire has [using the old thermostat and the wiring at the other end of the cable as clues] and to wire to the appropriate terminals on the new thermostat.

moonrakerz

DVardysShadow wrote: »

The correct way to approach this is.........

..........muckybutt has already answered that ..........:D

1984ReturnsForReal_2

DVardysShadow wrote: »

Works for the National Lottery, so there is a chance it will work for wiring.

The correct way to approach this is to work out what function each wire has [using the old thermostat and the wiring at the other end of the cable as clues] and to wire to the appropriate terminals on the new thermostat.

Agreed.

Google the wiring diagram for the old thermostat & bobs your .... oh whatever...

DVardysShadow

moonrakerz wrote: »

..........muckybutt has already answered that ..........:D

I think I have expressed it in terms which will make muckybutt's approach appear attractive.