New boiler cable running (Y plan)

[SteUK]

Hi chaps/chappettes,

Finally having our archaic 30+ years old boiler replaced for a sparkling new Bosch Worcester 18ri. In the interest of being as prepared and knowledgeable as I can be for when the gas safe installer comes to do the deed, I have been looking at potential pitfalls...and I think I have found one!

In a Y plan system, the old(current) boiler is fed from the airing cupboard via 3-core flex from a Honeywell 10 poll block. Assuming this is a switched live feed. New boiler will require a permanent 3-core live feed, along with a switched live signal wire, and needs to return a pump live and neutral. That brings the total up to 6 in total. What is the safest option for running new heat resistant flex cable? 3 x 3 core? (One for the perm live feed, one for the pump return, one for the switched live feed). I would like to run this cable pre-install, as it will involve moving everything out of a bedroom to get floorboards up (again :-/).

Thanks for your advice!

 

[D_Hailsham]

You only need five wires. The pump neutral can come from the main neutral terminal on the Honeywell junction box.

You will need a four core + earth heat resistant cable.

 

[ianmcd]

Agreed you only need 5 cores, this is what most of us use

http://www.ebay.co.uk/itm/5-Core-He...mponents_Supplies_ET&var=&hash=item4854f67413

 

[SteUK]

Awesome, I had heard of tapping the N off the 10 poll junction box in the airing cupboard.

I will be wanting a DP 3 amp switched fuse box as well I assume? Best to put boiler side I have read, so people can isolate directly at boiler end in the future. Doesn't this mean the 6 amp rated 5 core cable won't be protected though?

Cheers again

 

[ianmcd]

NO you need to run 2 twin and earth cables or 2 x 3 core cables to the fused spur next to the boiler one to feed the spur from the consumer unit and one to take the supply to your heating wiring centre so that when the fused spur is switched off it isolates the supply to the complete heating system and not just the boiler

 

[SteUK]

Confused now.

Currently there is a fused spur in the airing cupboard, fed from consumer unit, that powers timing unit, pump, ultimately boiler off switched live.

I thought best practice for boiler replacement was to run a twin and earth to boiler from there...and fuse switch it by the boiler (for the perm live feed to the boiler). Hence original question about running multiple 3 core for all the live, pump live, switched live required.

I guess what is currently there is the same as you describe, but everything is in the airing cupboard, not by the boiler. So best option with what is there...is to 3A switch fuse in airing cupboard and 0.75mm 5 core to the boiler from there? Or run solid core twin and earth from airing to boiler, 3A switch fuse and feed it to boiler perm live. Then run flex back from boiler to pump...and flex from honeywell in airing to boiler as switched live...?

Chairs!

 

[D_Hailsham]

You should have one, and only one switch/fused spur which isolates the complete system.

If you have two switches, downstairs and upstairs, an unsuspecting plumber will just turn off the one downstairs thinking that he has isolated the system. When he goes upstairs he may get a nasty shock.

It doesn't really matter which way round you do it: spur to boiler + five core to upstairs, or spur to upstairs + five core to boiler.

 

[SteUK]

Roger that! Makes perfect sense.

Just checked, airing cupboard switched fuse fed from consumer has 3A in it. So will just run 5 core from airing to boiler in advance of install.

Thanks for all your advice!

 

[ianmcd]

sorry but the fused spur must be adjacent to the appliance, with it being in the airing cupboard this would only be not to current standards if existing but the regs have changed and you cant install an appliance with NCS so your boiler installer should insist that the fused spur is moved adjacent to the boiler

 

[Steelmasons]

It's one hurdle trying to get additional cores down to boiler for perm live/pump overrun without the hassle of moving the spur from airing cupboard down to boiler FFS.

If spur is in airing cupboard when I fit a replacement boiler then it fookin stayes there.

 

[Dan Robinson]

Agreed you only need 5 cores, this is what most of us use

http://www.ebay.co.uk/itm/5-Core-He..._Supplies_ET&var=&hash=item4854f67413[/QUOTE]

Jesus that's expensive.

 

[Terrywookfit]

sorry but the fused spur must be adjacent to the appliance, with it being in the airing cupboard this would only be not to current standards if existing but the regs have changed and you cant install an appliance with NCS so your boiler installer should insist that the fused spur is moved adjacent to the boiler

How can a non gas related item be categorised as NCS.

It's got fook all to do with gassafe

 

[Dean744PiN5]

Sometimes i fit a fan isolator switch next to the boiler on a retrofit, just for ease of future maintenance really.