room thermostat

[Virtualcom13at]

Hi,

Question-A mains operated room thermostat requires three conductors to enable it to operate correctly. can you connect the thermostat to an existing two core and cpc cable and.

A=Use the earth
B=Use the earth and sheath with green and yellow
C=Use the earth sheath with brown
D=Not use at all

Im thinking you cant use the earth as your not allowed to use it as anything other than earth so that would rule out A + C. Does the Cpc cable count as one of the three conductors the thermostat needs to operate as its a bonding conductor ( I think ). or am i totally of the mark? I have only been studying for just over a month so be gentle.
Thanks

 

[truckster]

It depends on the roomstat, a basic bellows stat only needs a two core, live/switch live, an electronic stat needs the neutral to function and it also is used for a accelerator which stops the stat from switching on/off around the set mark.

The cpc is not required on many modern stats as the are class 2 but some still have a metal base and these need to be earthed. You can not use the cpc as a live or neutral conductor.

To sum up, if you have a twin in place use a standard bellows stat, if you are wiring new use a three core and earth to give max. flexibilty.

 

[Virtualcom13at]

It depends on the roomstat, a basic bellows stat only needs a two core, live/switch live, an electronic stat needs the neutral to function and it also is used for a accelerator which stops the stat from switching on/off around the set mark.

The cpc is not required on many modern stats as the are class 2 but some still have a metal base and these need to be earthed. You can not use the cpc as a live or neutral conductor.
To sum up, if you have a twin in place use a standard bellows stat, if you are wiring new use a three core and earth to give max. flexibilty.

But all we have is an existing two core and cpc cable. the thermostat in question requires 3 conductors. im confused! as i would say we cant use the existing cable as we cant use the cpc cable as a conductor but there is no option for this. unless thats what they mean by answer D.
hmmm have i just answered my question????

 

[telectrix]

yep, you just won the coconut. this happens frequently when someone wants to change a 2 wire stat for a 3 wire stat. can't be done without re-cabling in 3 core+E.

 

[Virtualcom13at]

yep, you just won the coconut. this happens frequently when someone wants to change a 2 wire stat for a 3 wire stat. can't be done without re-cabling in 3 core+E.

Happy days.
Cheers bud

By the way she always comes back out of tesco with the same baby because they never have what u want.:43:

 

[SyncroMan]

In the absence of any 3 core is it acceptable to run a second twin and earth and use one of the conductors, so long as the cpc's are connected?

 

[telectrix]

yes, as long as the new cable follows the same route.

 

[ringer]

Why does it have to follow the same route, tel?

 

[micknew]

Why not fit a wireless room stat?

 

[D80]

In the absence of any 3 core is it acceptable to run a second twin and earth and use one of the conductors, so long as the cpc's are connected?

Why not just pull in a PVC/PVC Single Cable if all you require is a 3rd core?

 

[SyncroMan]

Thanks for the replies.

I have to admid i'm probably being a bit tight not buying some 3 core or a wireless stat but ive got spare twin and earth and the wiring route is clear. I am just rewiring the house and that was one of the last jobs.

 

[Top Cat]

Why not just pull in a PVC/PVC Single Cable if all you require is a 3rd core?

I would say it would have to be 6241Y ie single core pvc/pvc + earth

 

[D80]

CPC would already be at stat and boiler/wiring centre from the Twin & Earth.

 

[grimysparks80]

The cpc is not required on many modern stats as the are class 2 but some still have a metal base and these need to be earthed. You can not use the cpc as a live or neutral conductor.

To sum up, if you have a twin in place use a standard bellows stat, if you are wiring new use a three core and earth to give max. flexibilty.

Shouldnt the cpc be continuous throught the circuit even if the room stat itself doesnt require one?

 

[Top Cat]

CPC would already be at stat and boiler/wiring centre from the Twin & Earth.

If you don't have an earth in the cable and it is buried in the wall someone could nail it and the nail would become live.

 

[D80]

If you don't have an earth in the cable and it is buried in the wall someone could nail it and the nail would become live.

I'm lost on how the CPC helps this, in normal 3 core what is to stop the nail/screw penetrating the live or switched lived only? Or on any cable even single and earth, only the live cable could be penetrated. Isn't this what the addition of RCD protection for cables embedded <50MM in the wall was for?

 

[Top Cat]

I'm lost on how the CPC helps this, in normal 3 core what is to stop the nail/screw penetrating the live or switched lived only? Or on any cable even single and earth, only the live cable could be penetrated. Isn't this what the addition of RCD protection for cables embedded <50MM in the wall was for?

Agree to a degree over this but at least you have a chance of the nail hitting the live and earth especially on a single cable.

 

[SyncroMan]

Does this mean my tight arse way of 2x twin & earth is safer,being as there is two cpc's?

 

[D80]

Would be safer if you had some steel conduit you could install it in:shades_smile:

I think your tight arse way is a more expensive way of doing it. But if its what you are doing you ma as well earth the extra blue conductor too, as its a redundant core at the moment. It is a fraction safer that you have the CPC and it could be hit at the same time as the live conductor with a drill, but you still require 30 mA RCD protection.

Is this rewire being notified?

 

[micknew]

Less than £50 for a wireless stat its a no brainer.