Wiring a boiler controller

Chrisknowlesuk · Jan 3, 2018

I need to wire a controller for an electric boiler.

Boiler is currently supplied via a 45amp breaker and a suitably large cable.

Controller needs a 240v supply. Instructions suggest this can come from boiler supply via a 3a fused spur.

Is it acceptable for this cable to be 2.5mm sized and a very short run of about 12inches to the spur. Or should it be equal size as the cable running to the boiler. Not sure if two cables that size would fit so the other option would be taking the power direct from the ccu and a 6amp breaker.

Technically it would not be protected if it were 2.5 coming from the boiler. I think I may have answered my own question but wanted to see what everyone else thinks

Thanks

robd · Jan 3, 2018

Can't you change the 45a breaker or is it an old one?

Spoon · Jan 3, 2018

There are lots of was to do it. I would not recommend a new circuit purely for this, in your case.
Where is the boiler relative to the CU?
Is there a ring main near the boiler. (That sentence is going to get some peoples backs up... Try doing scuba diving and call a 'fin' a 'flipper' and just watch all the angry faces..

)

Midwest · Jan 3, 2018

I'm going out on the edge here. As the FCU is limited to 13A, the 2.5mm cable ccc supplying the would not be exceeded. What do the manufacturers instructions suggest? Some gas boilers do have an output supply terminals, but I've never done an electrical boiler of this type.

buzzlightyear · Jan 3, 2018

Chrisknowlesuk said:
I need to wire a controller for an electric boiler.

pic would be nice .to what boiler you have .

Chrisknowlesuk · Jan 3, 2018

It’s very close to ccu. But an old one with no RCD so I’d rather not get involved in that.

Here’s the boiler pic

robd · Jan 3, 2018

Can't you put it through an RCD spur? A 47mm single surface box should give you enough room

Chrisknowlesuk · Jan 3, 2018

Thanks for the advice so far.

I’m more concern with having a short length of 2.5 coming from the boiler terminals to a fused spur as effectively this is being protected by the 45amp trip which would be no protection at all.

The way it’s wired at the moment is with no control or stat and botched.

I’ll see if I can find manufacturers guidelines for it.

Midwest · Jan 3, 2018

Chrisknowlesuk said:
Thanks for the advice so far.

I’m more concern with having a short length of 2.5 coming from the boiler terminals to a fused spur as effectively this is being protected by the 45amp trip which would be no protection at all.

The way it’s wired at the moment is with no control or stat and botched.

I’ll see if I can find manufacturers guidelines for it.

I did make a comment on that, #4, wait for another member to agree or disagree. What is the 'controller', and what does that 3core & earth cable do, connected into the boilers pcb terminals?

Leesparkykent · Jan 3, 2018

The usual way with an electric boiler that doesn't provide an output for external controls....like the potterton gold electric boiler you have is to have the control wiring fed through a 3A SFCU. The SFCU doesn't have to be from the Boiler power circuit. I wouldn't come from the boiler terminals with a bit of 2.5mm as I would suggest the connection with the larger CSA cable will not be one that's electrically sound. If the CCU is near by, like you say, then why not just run a new circuit for the controls?

Midwest · Jan 3, 2018

Looking at your pic, fear an additional set of wires into the main terminal isn't going to be successful.

Midwest · Jan 3, 2018

Looking at your pics, looks as if someone's already done what your suggest OP?

buzzlightyear · Jan 3, 2018

looks to me a 6kw heater .

Chrisknowlesuk · Jan 3, 2018

The current set up is a redundant controller which accounts for that 3 core flex and the two singles coming straight from the large terminals to the block where the controller would normally be. So it’s wired as permanently on via an external switch.

Just thought of a possible solution. If I took the 6mm cables from ccu to a switched spur. Take another set of 6mm from the supply side of the spur to the boiler. Then 2.5mm from the load side of the spur to control circuits.

Provided I can fit 2 x 6mm cables into supply side of spur this means all cables are suitably protected??

Does that sound correct.

buzzlightyear · Jan 3, 2018

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buzzlightyear · Jan 3, 2018

Chrisknowlesuk said:
The current set up is a redundant controller which accounts for that 3 core flex and the two singles coming straight from the large terminals to the block where the controller would normally be. So it’s wired as permanently on via an external switch.

Just thought of a possible solution. If I took the 6mm cables from ccu to a switched spur. Take another set of 6mm from the supply side of the spur to the boiler. Then 2.5mm from the load side of the spur to control circuits.

Provided I can fit 2 x 6mm cables into supply side of spur this means all cables are suitably protected??

what is the k/watt?

Leesparkykent · Jan 3, 2018

Chrisknowlesuk said:
The current set up is a redundant controller which accounts for that 3 core flex and the two singles coming straight from the large terminals to the block where the controller would normally be. So it’s wired as permanently on via an external switch.

Just thought of a possible solution. If I took the 6mm cables from ccu to a switched spur. Take another set of 6mm from the supply side of the spur to the boiler. Then 2.5mm from the load side of the spur to control circuits.

Provided I can fit 2 x 6mm cables into supply side of spur this means all cables are suitably protected??

Does that sound correct.

Erm no. I think you maybe a little out of your depth...prob best to get an electrician in.

buzzlightyear · Jan 3, 2018

POTTERTON GOLD INSTALLATION AND SERVICING INSTRUCTIONS Pdf Download. - https://www.manualslib.com/manual/812769/Potterton-Gold.html go on knock, self out !

telectrix · Jan 3, 2018

and did my eyes deceive me or is that a 3c/E with the cpc cut off? into the green terminal strip (that has more copper exposed than a capsized boat)

SparkySy · Jan 3, 2018

That is rougher than a hedgehogs back! Last one I did I bought the supply cable into a 2way con unit at the heater end with a 63a main switch for the heater and 6a mcb for the control side then they are both isolated by the mcb protecting the circuit at the main consumer unit.