underfloor heating question

Talk Electrician Forum

Help Support Talk Electrician Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

richardc

Junior Member
Joined
Jun 12, 2011
Messages
9
Reaction score
0
Hi I have three separate mats in a kitchen area with a Devi thermostat. I am trying to get information about wiring up a contactor switch for the mats. I have an IMO K2-23A10 contactor (see attached image).

Could someone advise me on where to go to get a wiring diagram. The unit has L1, L2, L3 on the top row and T1,T2,T3 on the bottom. Two separate green coloured terminals are on the right of the unit

http://www.richard-colson.co.uk/images/imok223a10.jpg

I would be very grateful for any quick assistance

richardc

 
Hi, if you wish to switch the neutral as well as the line conductors(preferable) then you will need a different contactor,

Otherwise,

terminals 13 & 14 i think are most likely the coil, and the L1 connects to T1 etc when energized.

Pics not great for me, Im on the phone. sorry.

 
Hello richardc, As Steptoe suggests a contactor is an eclectically operated switch, with open contacts that close when the coil is energised and have either two poles for double-pole, single-phase switching or three poles for three-phase switching. All contactors also have a pair of terminals that connect to the coil to operate the contacts. The wiring is just supply to one side and your load on the other and a trigger supply to the coil. You have what looks like a three pole contactor with what appears to be the CPC 'earth' connected to the coil? Earths would not normally be switched or used to supply a coil! Are you also aware that underfloor heating is notifiable work under Part-P building regulations? You may need to check if the manufactures recommend that the neutral should be switched or not.

Doc H.

you will need to check the manufactures instructions for the mats

 
NO. 13 and 14 are low current auxilliary contacts and NOT the coil.

Look for terminals A1 A2 etc that's the normal marking for the coil. They will be lower down on the body of the contactor.

L1, T1 etc are the main high power contacts. They are normally open, and when the coil is energises L1 connects to T1, L2 to T2 and L3 to T3

I'm not sure what that picture is trying to show, but to me it looks like it's wired wrong. It looks like someone has used L1-T1 to switch live, L2-T2 to switch neutral, and the auxilliary contact to switch the earth.

You should NOT switch the earth. Don't assume because for some strange reason the terminals are green, that they are earth terminals, they are not.

If that's your box (in fact even if it's not your box) rewire it so the earths joint together all the time.

Why do you need a contactor? is it just because the combined load of 3 heating mats exceeds the contact rating of the controller?

P.S, is it just me, or is this forum almost unusably sloooooow at the moment?

 
NO. 13 and 14 are low current auxilliary contacts and NOT the coil. Look for terminals A1 A2 etc that's the normal marking for the coil. They will be lower down on the body of the contactor.

I'm not sure what that picture is trying to show, but to me it looks like it's wired wrong. It looks like someone has used L1-T1 to switch live, L2-T2 to switch neutral, and the auxilliary contact to switch the earth.

You should NOT switch the earth. Don't assume because for some strange reason the terminals are green, that they are earth terminals, they are not.

If that's your box (in fact even if it's not your box) rewire it so the earths joint together all the time.
Agreed, Those earths need sorting out. It threw me seeing them connected onto any terminals of the contactor. Who wired this up in the first place? I keep looking at the picture trying to see where any wires are visible connected to the coil.

Doc H.

 
Hi Dave, Doc H and Steptoe

Thanks for taking the trouble to reply

I have understood that the two terminal A1 and A2 operate the coil and that these will be connected to the Devi thermostat that controls the switch

I have three mats with a combined load of 27 amps controlled by the thermostat

If I understand correctly the Live from each of the mats should be connected to T1, T2 and T3 while the mains supply from the CU will connect to L1, L2 and L3. The question of the neutral on each of these remains but it will not be switched. The earth wires will be removed from the switch altogether and connected together elsewhere.

I was not aware this was a building reg item. Unfortunately the firm (Neo Heat) that installed it in the first place do not exist any more. They used inadequate cable to connect the mats in the first place and these burned out twice because of this. I am trying to clean up after them and that's why I have bought the contactor.

 
Agree with the comments above - the earth conductors need to be resolved, before going any further.

Dave; I`d assume the contactor is for load issues; but, unless the mats are hundreds of feet long, the contactor is somewhat overkill.

Richard. 2 points, over and above what has been said above:

1. You may well find the contactor coil puts a back-emf pulse to the thermostat; which will lose all its time programs when the contactor switches OFF; unless a snubber capacitor is installed across the coil contacts, to absorb the pulse.

2. That contactor is WAY bigger than you appear to require; judging by the cables attached to it. Something like: http://www.tlc-direct.co.uk/Images/Products/size_3/WYMESB20.JPG

is more like the item you (probably) need.

HTH

KME

---------- Post Auto-Merged at 18:24 ---------- Previous post was made at 18:18 ----------

AH! reading your reply gives us this:

Your contactor isn`t really rated for the job - it would work as you describe; but you couldn`t switch the neutrals - unless the aux contact is rated 23A, same as the main contacts.

http://www.tlc-direct.co.uk/Images/Products/size_3/WYMESB40.JPG

in either a 2- or 4- pole configuration would be better; one for ALL lives and one for ALL neutrals (other than `stat. of course).

The capacitor point still stands however.

 
WOW.

27 Amps for the three mats. That's over 6KW, or over 2KW for each mat. Are you sure that's right? it must be a large area. All the floor heating mats I have seen have been measured in hundreds of watts, not thousands.

If it really is that large, then connect live in to L1, L2 and L3, and connect live out individually from T1, T2 and T3 to each heater, and of course unswitched neutral.

Regarding the Part P issue. I'm not up to speed as we don't have part P here, but that was a problem for the original installer. Since you are only sorting out his mistakes, could it be argued you are only doing a like for like replacement (of the burnt out wiring) so you yourself are not troubled by part p? is that how it works?

And can you clarify what wiring we are seeing for that contactor? is that your first attempt at solving this? if so you have got it wrong big time. you appear to have 2.5mm t&e in (old colours) and out (new colours) but if the load really is 27A then 2.5mm is not adequate to feed all 3 heaters.

P.S forum still stupidly slow for me. Is this just an issue for me? (other websites working fine)

 
Yes. Dave. It was wired incorrectly as you have said. I have taken that on board now. I will buy a snubber capacitor to ensure there is no back-emf pulse to the thermostat. I will wire live feed in to L1,L2, and L3 and live to mats on T1,T2 and T3. The mats are for a large kitchen extension room.

By "unswitched neutrals" to the mats do you mean connecting this with individual terminal strip connectors outside the switch?

With thanks

Richardc

 
They`ll be BIG "strip connectors" mate, to take 27A. Ylou`d be better having switched neutrals. If you`ve bought that contactor, I`d suggest changing it.

As Dave says - that 2.5mm cable isn`t up to that sort of load.

I thought you said it was wired like that? But didn`t you just buy that contactor? Confused!!!!

The neutrals really need to be switched - what is the local isolation for the circuit?

Could you post piccies of exactly what you`ve got there, where the feed comes from, etc? Thanks.

KME

 
Hi Richard, from the posts above and the new pictures the state of the installation is becoming clearer, you have indeed been left with a mess.

The original wiring was not up to standard. Most under flooring mats are 100w per sqm, or 200w per sqm, in larger areas it is usual to have more than one thermostat, so that the loading is shared. First of all all what is the maximum switching in amps is the thermostat, do you have any instructions for it that tell you? This will not be a problem if you do go via a contactor, but I would interested to know. All the neutrals should be connected together, so that they do not switch, this is a safety feature, in the event of any failure, the terminal blocks used are not really adequate for this job, a better option would be some maintenance free, lever/push fit connectors, which will tidy up the job. Connect the live wires as suggested above. I am sure KME will be back and fill in the blanks I have left.

 
Hi KmeHere are some images of isolator and thermostat

32 Amp cable comes from Isolator to the switch.

Pictures show wires to mats and the termostat + feed from Isolator Unit

http://www.richard-colson.co.uk/images/IMG_2186.jpg

http://www.richard-colson.co.uk/images/IMG_2184.jpg

http://www.richard-colson.co.uk/images/IMG_2183.jpg

http://www.richard-colson.co.uk/images/IMG_2185.jpg

I appreciate your replies

richardc
ive been to one of these where they had been through a few of them progs, manufac say more progs (but then again they would) as theres a limit (in square m size) to how many matts one can run and also using a contactor sometimes makes them go faulty, but adding the capacitor like KME said would prob overcome that... clever fella

 
Hi Manator

Thermostat is a Devireg 535 Op voltage 180-250 VAC 50/60HZ

Resistive load 230V ~ 15A/3540W

Thanks

 
Hi ManatorThermostat is a Devireg 535 Op voltage 180-250 VAC 50/60HZ

Resistive load 230V ~ 15A/3540W

Thanks
So the switching load of the thermostat is half the load it's been trying to switch. No wonder it keeps blowing them.

I still question the rating of the mats. Have you actually tried measuring the current drawn by each mat? At say 200W per square metre, that makes this a 30 square metre kitchen. Large to say the least.

 
I have installed this on matting (and larger) from one `stat. They tend to generically be 15 or 16A resistive loading (which is part of the contactor issue - its an inductive load;) )

OK - thanks for the pics. As the guys have alluded, the install doesn`t look good (understatement).

You could use the devi to switch 1 mat and the contactor, and put the other two mats through the contactor - it would work, but its neither ideal or elegant. Those strip connectors don`t look like 32A rated; and the twin & earth cable looks suspiciously like 2.5mm; if so it simply isn`t big enough.

I concur with Prodave r.e. testing the ACTUAL load of the mats (do `em individually on a plug ;) ) (Dave - forum isn`t slow with me.......yet).

I would be tempted to start again from the isolator and mat tails, and completely redo the control & switching sections inbetween. It is worth pointing out that somewhere, you need a fuse to protect the low current switching circuit - and I think you`ll struggle to get it in that little enclosure with your big lumpy contactor, and a snubber............unless you were planning to wire the `stat in 4 or 6mm 6491 or tri-rated singles?

Hope that is of some use to you mate?

KME

 
can I interject for a moment here.

can we ask the OP just exactly what is his standing with regards to experience?

are you a diyer/homeowner trying to sort out a mess you hyave been left with

or

a spark that hasnt come across this before?

I think this will help us understand how best to explain and direct this thread to a better conclusion rather than baffle with BS or Dazzle with brilliance. :D

 
From the posts steptoe I think Richard is an educated DIY,er, trying to save the mess he has been left with. As this is a repair, and replacement of faulty wiring I would think it would be just borderline with Part P, however it would be faster if a qualified electrician was there to sort it out. Probably costing not that much, but again it is in London, so I would not know.

 
Hi Dave

Yes it's 35 sq m. It's basically two rooms together to form a kitchen/dining area

Do you think I need to install two thermostats?

richardc

---------- Post Auto-Merged at 08:52 ---------- Previous post was made at 08:48 ----------

Hi All

Any names of qualified electricians who might sort this out for me? (London)

richardc

---------- Post Auto-Merged at 09:01 ---------- Previous post was made at 08:52 ----------

Hi

Yes. I feel I have been let down by the electricians who installed this. I have a great deal of experience as a DIY installer but have not ever dealt with contactor switches before. This is outside what I have had to deal with. The initial install by the U/F heating firm (New Heat) was wrong so I employed an electrician to sort it out. He left me with two of the mats working but did not return to finish what he had started. I know that another electrician might not want to take on a job started by someone else so that's when I got on the phone myself and was advised about the equipment etc

richardc

 
Hi Richard, we have members of this forum who cover your area, maybe they can help you out. If it is any consolation, I can not paint, anything near as good as you, and my clients have never been as prestigious as yours. I am sure some offers of help will be forth coming.

 
Top