4 core isolation.

[kaboom]

Hello guys, can't get hold of my spark to ask today and need a clue to prepare a job so-
I want to add local isolation to a four core (LNE and switch live) flex to a boiler. Is there a switch that incorporates the extra terminal?
Thanks.

 

[shortcircuit]

There should only be one supply to the boiler and that should be from a switched FCU which isolates the Phase and Neutral. The earth should not be isolated. The switchwire should be an integral part of the boiler circuit fed from the previously mentioned FCU.

If you have a switchwire fed from elsewhere, your out of your depth and need competent advice

 

[plugwash]

so long as theese are low current wires (as they probablly will be in a central heating install) a 3 pole fan isolator should be ok.

most central heating systems just have a FCU for the whole system though is there any particular reason the boiler needs to be seperately isolatable?

 

[Lectrician]

Agree.

NEVER isolate the earth

 

[plugwash]

unless you have two supplies with earthing systems that must not be interconnected

 

[kaboom]

Fused switch and control box in upstairs airing cupboard. Boiler downstairs in kitchen. New boiler needs 4 core (old was 3). My understanding was that the boiler should be capable of being isolated locally. Am I right? Just want to have the right bits in the right places for elecrical man when he re-appears..

 

[Lectrician]

Yes, the boiler needs local isolation. This is more a plumbing rule than a sparky rule, as if the remote isolator can be locked off, it complies to lecky regs.

 

[kaboom]

The whole lot can be shut off from the fused spur in the airing cupboard, but if I have local isolation for the boiler in the kitchen- as its a 4 core supply from the wiring centre, I assume (assumption being the mother of all fekups) that I need a switch that will accomodate both lives?
PS. Who said anything about isoating the earth?

 

[Moss5]

The extra wire may be a frost protection live (not timed). If you are offering isolation close to the boiler, a 3-pole switch would be required. A .pdf is available here.
http://www.tlc-direct.co.uk/Technical/DataSheets/MK/Index.htm

 

[Lectrician]

Boilers, worst case, will have a LIVE, FIRE and NEUTRAL.

They may also have a switched pump live OUTPUT - this doesn't need isolating.

 

[kaboom]

Sorry if I'm frustrating/confusing anyone. Should I have said 3 core and earth?
Yes Lectrician, it has a live to power the display and brains and a switch live to call for heat. Is there a three pole equivalent to a normal fused switch or is the fan switch mentioned earlier the only answer?

 

[Lectrician]

The 3 pole fan isolator is the only answer.

I generally make sure I put the FCU for the entire heating system at the boiler, and wire from here to the wiring centre. You still only need 3 core and earth from it to the wiring centre, unless there is pump over run. It does mean putting a feed to the FCU at the boiler end, but if you didn't do it there, you would have to at the other end anyway!

 

[kaboom]

Thanks.