Quick questions - CM67 RF Stat

No. It must come off the same circuit as the central heating itself. Otherwise, there won't be a single point of isolation for the heating system. Many boiler manufacturers insist that any control electronics are wired from the special outputs from the boiler so that the boiler internal isolator also disconnects the power from the controls. If there is no auxilliary mains supply from the boiler, wire into the boiler supply FCU.

You are scaring me.

Use 1.0mm mains cable or flex.

Christian.

It must share the same switched supply as the the rest of the CH/HW system. If you use another source of power bits of the system will still be live when the main CH/HW switch is off.

Very unlikely. The vast majority of control systems switch mains, you must use mains rated cable.

It's questions like this that almost make me think Part P is a good idea after all.

I'm not using telephone wire for the electric part, I'm refering to the temp sensor part....

paul

I'm not sure I'm getting you.

All electrical connections should be considered to contain 230V. Even if some combis use low voltage signalling, its replacement may not.

Christian.

Why not just run a 3 core (+earth: only professionals use the green/yellow as a switch wire) from the boiler. Sound practice dictates that one switch isolates all the heating system.

Less so now I suspect. On my Glow-Worm combi the instructions make it pretty clear that they would much rather you used the LV terminals connected to a volt-free thermostat but if you really insist you can do things the traditional way.

The OP's logic is that he is connecting the low voltage mains-free contacts on the boiler to the relay contacts on the CM67 so that all you need is bell wire. And if the workmanship is OK there is no chance of either of the two mains feeds interfering with the other. But it's not the way to do it.

What, precisely, are you talking about?

I can only read "What sort of wire should be used to connect the stat to the boiler?" to mean the connection from the CM67 RF receiver unit, "stat", to the boiler. This is almost certainly mains.

I think he means for the optional remote or outside sensor - is that right Paul?

In which case the remote sensor installation PDF states that twisted pair must be used - it doesn;t say it needs to be mains voltage rated. But it would need to be mains rated if it were to be run in the same group or trunking as mains installation cables. Best to route seperately away from the mains.

So telephone wire would be OK as long as it is twisted pair and you use both conductors from a single pair. Or use CAT5 or similar networking cable. AFAICS anyway.

I'd have to say that I read Paul's message as use phone wire for the demand to boiler connection until he clarified it.

HTH

Tim

Have just found the manual - it says use 3A cable, so that is what I'll use.

thanks. Paul

I meant exactly what you've said above - I will be using 3A cable.

paul

It also needs to have suitable insulation resistance, for example. Extra low voltage (i.e. automotive) cable may not have sufficient insulation rating. Use 1.0mm T&E mains cable for fixed wiring, or you can use pretty much any mains flex if the box is adjacent.

Christian.

Your professionals are just messing about using the correct coloured sleeveing. A *real* professional just wraps the earth wire in black insulating tape, if your lucky... B-)

Who said his boiler has LV volt free contacts? He has an Ariston Microgenius that I believe requires its live mains to be switched by the room stat relay box. Volt free refers to a relay which has nothing connected to any of its contacts - that is what is in the CM67 box. In other words it is a 'proper' mechanical switch not a digital signal. It won't be volt-free once the boiler is connected to it!!

Phil The uk.d-i-y FAQ is at

The CM67 relay box is double insulated and has no earth connection. It requires 2 core mains for its supply and ditto for the relay (both 3A rated I believe). Its construction makes it nearly impossible to use a single 4 core for this.

Phil The uk.d-i-y FAQ is at

Huh?? The temperature sensor part is battery operated - it does not have any wires connected to it.

Read the instructions - you might need a magnifying glass though.

Phil The uk.d-i-y FAQ is at

Just twin. It does not have an earth.

Phil The uk.d-i-y FAQ is at

Personally, unless the device is adjacent to the wiring centre/boiler (which in this case, admitedly it is) I would always run an earth even if not needed. The next zone valve/chrome plated thermostat etc may require one.

Christian.