Underfloor heating connected to the light switch.

Josh2k · 31 Oct 2014

Hi, I could do with some help on what maybe an easy fix.

I have recently moved into a house. I have an issue with the bathroom setup between the lights and electric underfloor heating.
The underfloor heating seems to be wired into a double switch that controls the lights and an extractor fan. The fan operated on it own but when the lights are turned on/off the floor heating also turns on/off with it.

This is rather pointless as the floor is tiled and above an external porch and is therefore freezing most the year, and it takes a good 15 mins for any heat to be felt once switched on. I would like the heating to be powered all the time as I think it was designed to be as you can set your own schedule from the control panel. Every time it is turned off at the moment the schedule is reset.

I have taken the switch off the wall and had a look at the wiring. I have attached a very rough drawing of the rear of the switch. It is not clear to me which wire is coming from where to determine what they are connected to. There are five red wires connected to the switch, another red wire connected between the two COMs and a brown wire coming into one of the Live points.

Is this an easy fix and just a mistake when it was fitted? Should it be connected to the light switch, or is this dangerous?

I should point out the underfloor heating has its own fuse switch on the wall which also comes on and off with the lights.

Thanks for you help

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Josh2k
31 Oct 2014
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Josh2k · 31 Oct 2014

securespark · 31 Oct 2014

It looks like you have 3 switch wires coming off the light switch.

The easiest solution would be to identify the feed to the heating and move it to the Common terminal.

But you really need to identify what circuit the heating is on.

Does the lighting go off with the fused switch as well as the heating?

Josh2k · 31 Oct 2014

No the lighting stays on.

So you think there are too many red wires in the live terminal and one just needs moving to the Com from the light side?

ericmark · 31 Oct 2014

It is no good guessing. It could very well be an independent supply to bathroom with bathroom lights and heating only, it could also supply all other lights in the house.

There is a good reason why it is recommended not only to do a EICR every 10 years but also on change of occupant.

So question one what did the electrical installation condition report (EICR) say?

If you have decided to take a chance without one then at least start at the beginning. Get a bit of paper or note book and switch off all the MCB's or pull all fuses then replace one at a time going around the house finding out where every device is fed from. You may as well do the lot now it will help latter if anything fails you will know where it's fed from.

So next is to report what MCB/FUSE/RCBO/RCD is the lights and heating fed from. Size and type and then people on here will be advising with some back ground not stabbing in the dark.

ban-all-sheds · 31 Oct 2014

securespark said:
Does the lighting go off with the fused switch as well as the heating?

Josh2k said:
No the lighting stays on.

By the sounds of it:

Josh2k said:
I should point out the underfloor heating has its own fuse switch on the wall which also comes on and off with the lights.

The heating FCU is downstream of the light switch.

Which is bizarre and pointless.

ban-all-sheds · 31 Oct 2014

Josh2k said:
So you think there are too many red wires in the live terminal and one just needs moving to the Com from the light side?

If you do that then whatever is switched by that gang will be on all the time.

I'm concerned that you don't actually know what a switch does, as in how it works and what it does with conductors connected to its various terminals, and that therefore you probably shouldn't be fiddling with your electrics.

underfloor
And ^ heating should not be on a lighting circuit.

Please get an electrician.

[EDIT]Clarification added[/EDIT]

westie101 · 31 Oct 2014

And heating should not be on a lighting circuit.

So those combined electric heaters and lights that were sold for bathrooms and quite legally connected, never existed?
Or the 750W infra read electric fires that were fitted

Is not the restriction on a lighting circuit more related to connected load?

deadshort · 31 Oct 2014

The brown wire maybe the ufh supply if you remove the FCU you can identify the cable i.e., Brown and Blue ?

The feed to the FCU can be connected to the com terminal that will allow you to control the heating, i assume you have a programer for the heating? The load must be OK for the lighting circuit or the mcb would trip if it was overloaded.

NB you must have rcd protection on the circuit.

Regards,

DS

JohnW2 · 31 Oct 2014

deadshort said:
The load must be OK for the lighting circuit or the mcb would trip if it was overloaded.

Given that the UFH is currently only coming on with the bathroom light, it presumably is never on for very long, so the current could considerably exceed the In of the MCB without it ever tripping. However, the cable would be deemed to be adequately protected by the MCB.

Having said all that, and assuming it's a lighting circuit, even if the circuit is wired in 1mm² (and certainly if it is wired in 1.5mm²) cable, the actual CCC would be way in excess of the In of a 6A MCB, so the cable is , pretty unlikely to be overloaded (the limiting factor being the MCB, not the cable's CCC).

Kind Regards, John

deadshort · 31 Oct 2014

'the mcb would trip if it was overloaded' If it didn't what is its function?

Kind regards,

DS[/b]

333rocky333 · 31 Oct 2014

That is its function but it wont trip instantly, unlike a "Deadshort" where its likely to be pretty instant

deadshort · 31 Oct 2014

Yes, and a BANG ! don't forget the Bang

Regards,

DS

deadshort · 31 Oct 2014

deadshort said:
The brown wire maybe the ufh supply if you remove the FCU you can identify the cable i.e., Brown and Blue ?

The feed to the FCU can be connected to the com terminal that will allow you to control the heating, i assume you have a programer for the heating? The load must be OK for the lighting circuit or the mcb would trip if it was overloaded.

NB you must have rcd protection on the circuit.

Regards,

DS

P.s if you don't have a programer on the ufh that maybe the reason it was wired to the light switch? If it was left switched on at the fcu for hours ?

DS

JohnW2 · 31 Oct 2014

deadshort said:
'the mcb would trip if it was overloaded' If it didn't what is its function?

That depends upon what you mean by 'overloaded'. A circuit is technically 'overloaded' (and certainly non-compliant with regs) if Ib>In. However, if the design current exceeds the In of the MCB by less than 13%, it should never operate, and much higher degrees of 'overload' (the extent to which Ib exceeds In) than will be tolerated (without MCB operation) if their duration is limited.

The 'CCC's ("In") for cables we work with have hopefully been devised such that an MCB with an In no greater than that 'CCC' will adequately protect the cable from damage if it is overloaded (carries a current in excess of that 'CCC'), but that does not alter the fact that such is technically an 'overload' situation - and the MCB may not operate if the extent and/or duration of that 'overload' is not great enough to be deemed to threaten the cable.

Kind Regards, John

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Underfloor heating connected to the light switch.

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