What size cable from boiler to cyl stat?

[Kes]

Can some kind person tell me what size cable I need to use to connect a Horstman HCT2 cyl stat to an oil boiler programmer? I assume that the current through this cable will be low, i.e the whole boiler burner/pump etc won't be passing through it, but the stat will energise relays in the boiler? Ta.

 

[aptsys]

Typically 1.00mm², but it should be rated appropriately, so if the circuit is protected by a 13A fuse, use 1.50mm²

 

[gas4you]

Oil boiler heating electrical cicuits should be protected by a 5 amp max fuse and gas 3 amp. Most visible wiring should be heat resistant 0.75mm2 flex.

 

[Kes]

Thanks for that. I shall go for heat resistant round flex. I have to make the usual three connections: there is plenty of three-core h/r flex available, but the 'third' core of course has the green/yellow earth insulation. Is it bad form to use such cable, or is it common practice if the 'earth' wire is sleeved brown? (There is no earth connection as such to the stat).

 

[electronicsuk]

You should use 5 core, it isn't acceptable to use the green/yellow CPC for anything other than an earth connection. There is usually no need for heat resistant/butyl flex unless connecting to an immersion heater or synchron valve.

 

[gas4you]

You should use 5 core, it isn't acceptable to use the green/yellow CPC for anything other than an earth connection. There is usually no need for heat resistant/butyl flex unless connecting to an immersion heater or synchron valve.

What about boiler connections? As the HW cylinder can reach quite high temp I would always use it.

4 core is plenty for a cyl stat, where would you need the 5th core for

 

[electronicsuk]

What about boiler connections? As the HW cylinder can reach quite high temp I would always use it.

I wouldn't normally bother for boiler connections, certainly not with more modern units. The control boards and connections are generally housed toward the bottom, well out the way of anything that generates excessive heat. Many/most of the leads soldered to the PCB don't have heat resistant insulation either.

4 core is plenty for a cyl stat, where would you need the 5th core for

Valid point. Just personal preference on my part I'm afraid, 5 core isn't really much more expensive or hard to get hold of than 4 core, and you never know what you might need in the future. Of course, using 4 core does mean that you could use 3C + E flat rather than flex.

 

[gas4you]

A lot of modern boilers now have the electrical connections come up through grommets in the bottom of the boiler casing before entering the pcb area. Anywhere inside the casing could be liable to get pretty hot.

Think you will find most boiler MI's state heat resistant flex.

I always carry a drum of 2, 3, 4 & 5 core heat resistant flex on my van.

The only one I've had trouble finding in heat resistant is black 2 core, for my installations with weather compensation.

 

[Lectrician]

I keep 3, 4 and 5 core heat resist on the van as we do a fair amount of cent heat. Always use 0.75mm.

Use cable for the fixed side of the wiring, and flex for the final drops to the boiler, cyl stat, pump etc etc.