Central heating programmer cable 3 and earth

[Paul Dodds]

Hi,
Hope you're all doing well. I have a customer who needs a 5 core cable to the boiler from the wiring centre. At the moment the feed is coming from a 13a socket in the upstairs cupboard through the programmer into the wiring centre and then 3 and earth under bathroom floor and into the kitchen. In order to get the 4th cable they were using the earth. The plumber has obviously put this back to its original purpose but now there's 1 cable too few - line, neutral, earth, call for heat and call for hot water.
Under the boiler is a fused spur for the cooker hood. Is it possible to use this as the feed for the boiler allowing the line or neutral cable to be used for the call for heat?

I hope this makes sense. Sorry I should have taken pictures but thought of posting here with this "fix" after I left!

Cheers

Paul

 

[Midwest]

Think OP saying he wants to alter use of existing 3c & earth, and then add new supply?

What is the existing 3c & earth cable?

 

[nunthe wiser]

Or spur programmer from a separate source,using outputs to switch relays, live and 2 switch lines. That should be possible. Never interconnect 2 circuits.

 

[nunthe wiser]

Or spur programmer from a separate source,using outputs to switch relays, live and 2 switch lines. That should be possible. Never interconnect 2 circuits.

 

[nunthe wiser]

Presumably 3c and e was used as pl n ch hw. So he’s lost a sw line due to cpc being reinstated

 

[Lucien Nunes]

The nub of this is doing away with the N in the 3c+E that is difficult to replace.

If the programmer has fully isolated volt-free contacts, you can power it from one circuit while controlling another. The programmer L & N would be sourced locally, while the 3C+E brings a PL from the boiler circuit to the contact common and returns the CH and HW outputs. Two circuits would be present in the programmer and there is a risk of later alterations accidentally linking the circuits together. Not sure how you would address those risks in a domestic install.

Or, if the programmer doesn't provide isolation between the contacts and supply L, or to avoid two circuits in the programmer, you would need to add relays as per above. Power the programmer locally, use the 3C+E to send CH, HW & N to near the wiring centre, where two relays control the boiler circuit. Now the two circuits are present in the relay box instead, which can have suitable prominent labelling, and the separation is less likely to be breached.

 

[Wilko]

Not sure if I've understood correctly, but thought maybe use a "wireless switch" to replace the missing conductor (?). TESTED: RF Solutions MAINSLINK - http://professional-electrician.com/products/tested-rf-solutions-mainslink/
FWIW, I would only use a single circuit with a single point of isolation .

 

[buzzlightyear]

can I had, if another gas engineer turns up ,boy he would not like that having two sauces of power ,either rip out and start again and sod the tiles or work under Neath the flooring .e.g. plaster board if possible .

 

[Deleted account]

Not really suitable mixing 2 circuits, if they are either side of a split board you'll run into issues

Agree with above. Even if it's not a split board it's still not a good idea to mix one system with 2 separate circuits.
You need to be able to isolate the whole system at one point.

 

[Deleted account]

can I had, if another gas engineer turns up ,boy he would not like that having two sauces of power .

Yep! Never mix hienz and Daddy's.

 

[Leesparkykent]

If you can’t get a cable in then I’d fit a RF mains link as linked to above.

 

[Dave OCD]

Just to add something else [And haven't wired a Y plan for ages so could be wrong], but don't you also need a switched 'HW off' core from the programmer on a Y plan too ? If so that would be six cores in total.

 

[Leesparkykent]

Just to add something else [And haven't wired a Y plan for ages so could be wrong], but don't you also need a switched 'HW off' core from the programmer on a Y plan too ? If so that would be six cores in total.

I read it as the OP needed 5 cores to the boiler not the programmer. If it is the case that you describe then he could install a relay. Use HW on to energise the coil and wire the grey of the mid position valve and normally open of the cylinder thermostat to normally closed of the relay.

 

[Toneyz]

I would not recommend having a central heating system with 2 points of supply ..... And isolation

The answer is NO only one supply and point of isolation. You will need to install a new cable.

 

[Dave OCD]

I read it as the OP needed 5 cores to the boiler not the programmer. If it is the case that you describe then he could install a relay. Use HW on to energise the coil and wire the grey of the mid position valve and normally open of the cylinder thermostat to normally closed of the relay.

I probably misunderstood Lee, it's that time of day when my old brain has had enough.

 

[Toneyz]

Is this a separate programmer?