cable size

[graham14]

Can someone please tell me the minimum cable size to connect a room thermostat (Grasslin thermio 103) to a Biasi combi/ Condenser boiler. I presume I only need a two core cable.

 

[ChrisR]

Don't presume, check the instructions. It will be in there.

0.5 sq mm would be heavy enough to carry the current but it's fairly thin & fragile, so many boiler mfrs recommend 0.75 sq mm flex.
You can only use flex at all if the thermostat says you can - it would need a cable grip. Otherwise it's "fixed wiring", = solid core cable. Boilers usually have cable grips.

 

[chrishutt]

What do the instructions say? You can't install it without reading and understanding the instructions.

 

[Slugbabydotcom]

While 0.75 is recommended for the power supply; the thermostat circuit is only carrying enough current to operate a relay on the pcb so you can often use bell wire if you want. Anything bigger than 0.75 flex is overkill and probably wont fit in the terminals.

However I am making assumptions here so DONT TAKE MY WORD FOR IT
Call Biasi on 01902 304 400 and find out for yourself

 

[graham14]

Thanks for the advice, noted

 

[ChrisR]

Bell wire might not be rated for 230V !

 

[breezer]

use 1mm twin and earth cable not flex

 

[chrishutt]

And if the thermostat has an accelerator?

Best to read the instructions.......

 

[breezer]

since bell wire was mentioned i assumed it had no internal resistor, looked it up on google, it has, so make it 1mm 3 core and earth (no need for instructions with google)

 

[chrishutt]

And what if the boiler has voltage free connections for roomstat / timer?

Best to read the instructions...

 

[breezer]

And what if the boiler has voltage free connections for roomstat / timer?

Best to read the instructions...

if it does the room stat suggested will be of no use, since it gives a switched live (i read the instructions)

 

[chrishutt]

(i read the instructions)

Exactly

 

[breezer]

(i read the instructions)

Exactly

(Arnold swazenegger voice*) I lied


*Matrix: Remember, Sully, when I promised to kill you last?
Sully: That's right, Matrix, you did!
Matrix: I lied.

 

[PEDANTICVINDICTIVEMAN]

Hey guys surely the cable connecting into the boiler will need to be heat resist which is normally sold .75m, thats what I use anyway and end up running it all the way to the stat, then if it runs against a hot pipe say in the loft space it's more protected.
Because the regs change weekly maybe I am wrong and you can use standard cable now.

 

[ChrisR]

Hey don't tell anybody but I expect that's what most of us use.

If anyone knows the latest for sure maybe they could also tell us when to use the relatively cheap Heat Resisting flex and when (and why) the Butyl rubber one which is £££.

One answer of course is that mains cables should be kept away from pipes and not share a duct.