Mystery Fault with Electric Underfloor Heating

[DetlefSchmitz]

Earth Leakage Clamp Meter , what defines the "earth leakage" part of the name compared to a Clamp Meter ?
I just thought that a clamp meter is a clamp meter and depending upon its range, resolution and accuracy then it can be used as the user decides

How long did it take you to find the clamp meter you bought that was suitable for measuring whether earth leakage was the issue in an investigation into why an RCD might be tripping, and how much did you pay for it? I would assume that the one you bought can reliably distinguish between 5ma and 6mA earth leakage, to use a random example.

 

[ebee]

Well , current that is going to Earth, call it Earth Leakage if you like, I have no objection to that.
It is just naming the particular test meter that I am objecting too, you might have Phase to Phase or Phase to N or Phase to E, or even N to E currents, both high or low that you want to measure, either directly as one conductor or residually with two conductors , so the "Earth Leakage" part of the name of one of those meters is a misnomer.
I mean, I could call a claw hammer a "Glass Smash Hammer" but I could smash other things with it or hammer nails in with it or I could smash glass with loads of other things too.

 

[EFLImpudence]

I mean, I could call a claw hammer a "Glass Smash Hammer" but I could smash other things with it or hammer nails in with it or I could smash glass with loads of other things too.

The criterion for such a name is not whether you can smash other things with your "Glass Smash Hammer" but whether other hammers cannot smash glass; much the same as the reason it is called a "claw" hammer..

 

[Agile]

One thing I did struggle with when I took the pictures was that I could not put the RCD back on - it just wouldn’t stay put and after 10 or 15 attempts it decided to stay put. The heating switch that caused it trip was off so it had no reason to not stay put.

Thanks

That makes me think that you probably have more than one circuit which has some leakage. If the RCD does not reset there must be a leakage current flowing. The associated neutrals also have to be connected to the correct RCD group.

My first approach would be to examine how this UFH is physically fitted. Has any of it been damaged or become damp?

The usual cause of an RCD tripping is a leakage from the live to the "actual earth" and most often caused by dampness coming into contact with a live wire.

I went to a gas boiler which was tripping the RCD after a few minutes of operation and several people had been to see it and unable to diagnose the fault so the owner clearly had little expectation that I could. I chatted with him for a few minutes and took the front of the boiler off and distracted him to make me some coffee. While he was out of sight I disconnected the remote room stat connections and bridged the connections.

When he returned with my coffee I asked him to turn the heating on which he did. I took a few sips of the coffee and watched his amazement. After perhaps five minutes he said it had never stayed on for so long before! I explained what I had done and after some forensic questioning he admitted that the thermostat wires had been extended under the floor. We deduced they had carelessly been twisted together without adequate insulation and were in contact with the damp earth under the floor. I could have measured the leakage to earth and most RCDs are designed to trip if the leakage exceeds 10 mA. On that particular boiler the room stat connections are powered with mains voltage. Most modern boilers either have a choice of mains or low voltage ( usually 24 vdc ) and the installer chooses which he wants to use. Some older thermostats have a "heat anticipator" which is a mains powered resistor which gives out a small heat to improve the response.

 

[ebee]

The criterion for such a name is not whether you can smash other things with your "Glass Smash Hammer" but whether other hammers cannot smash glass; much the same as the reason it is called a "claw" hammer..

OK then, a claw hammer is for smashing claws with, I always thought it referred to the "Claw" on the opposite side from the head and commonly being used for pulling nails out.

Other, current clamps, for amps, tens of amps or even hundreds of can still help for testing "leakage" to earth or other places (N or another phase) just like the ones with smaller resolutions.
Not all earth fault paths are tiny some can be quite large (in relation) , I would be happier if they were just called current clamps as the ref to earth leakage could be misleading although I do see that some that are accurate at much smaller currents can be more useful sometimes.
In short, it is the actual term "Earth Leakage" part of the common title I am not over happy with.

I suppose if we were to rename them as "17th Edition Current Clamps" it would not be much help either!

Actually, one thing I do find troublesome with current clamps (of any resolution) is folk using the to measure the current in an earth conductor rather than the residual current in Live conductors, that can be very misleading sometimes

 

[EFLImpudence]

Actually, one thing I do find troublesome with current clamps (of any resolution) is folk using the to measure the current in an earth conductor rather than the residual current in Live conductors, that can be very misleading sometimes

That is not anything troublesome with current clamps; it is folk not doing things correctly who are doing things wrongly.



Here's one for you:

Unfused spur.

 

[ericmark]

So - what do you call current that is leaking to earth?

Lighting?

how much did you pay for it?

£35 with 1 mA resolution, OK maybe we should be able to measure 3.5 mA, but over 3 mA then should not be using single earth and 13 amp socket, do we really need to measure 3.5 mA?

That makes me think that you probably have more than one circuit which has some leakage.

Now we are talking, this is my point, we need to ensure it is the UFH at fault.

I luckily found when a builder had caught the UFH and twisted wires together and said nothing, unlikely his electrician would have found it, as he turned up without even an insulation tester, Part P had just come in, but it seems that electrician had not caught up.

We can pick people up for using wrong names, live instead of line, low voltage instead of extra low voltage, and yes there are times wrong names can throw one, but in the main, it hardly matters, I know I have a fault in my own house, before solar panels were fitted I had around 19 mA to differential, after about 8 mA to differential between the tails to the consumer unit, and the 3 freezers and central heating are now not fed from the consumer unit, so it does seem likely there is a fault somewhere, likely the central heating. It is on my to-do list, as is fitting a RCD FCU to the central heating supply. I left it as a summer job, so time to correct any faults. But without the clamp on, I would have no idea there was a fault, and since issued a compliance certificate if I was not an electrician would have not given the moving of the central heating to a non RCD protected circuit a second thought.

But does it really matter if called an imbalance, a differential, or earth leakage? We are not sitting an exam where they are trying to catch us out with phrases like "and others" which was with 17th the difference between skilled and competent.

Yes, something is causing an imbalance, and yes

Some older thermostats have a "heat anticipator" which is a mains powered resistor which gives out a small heat to improve the response.

and I have seen this connected to earth rather than neutral, but what we are looking at is a system where an electrician has tested it and found no fault, so one would hope errors like that would be spotted! Also see green/yellow used as a live wire, even seen it used as a line wire. "The bi-colour combination green-and-yellow shall be used exclusively for identification of a protective conductor and this combination shall not be used for any, other purpose." note full stop, but it continues "Single-core cables that are coloured green-and-yellow throughout their length shall only be used as a protective conductor and shall not be over-marked at their terminations, except as permitted by Regulation 514.4.3." and I have had people say therefore one can use the green/yellow core of a multicore cable! And over sleeve. They must have done a different English class to me?

We know we should not do it, they are clearly clutching at straws as they did not have four core on their van, however errors like that can escalate, one sees a green/yellow and instinctively connect it to earth, we simply don't expect some idiot to have used it as a live, even if used for neutral, the neutral is still classed as a live wire.

So yes that is one easy missed, but can't see how one would fail to find it with standard meters carried by electricians, if a plumber has attended (no slight on @Agile ) I could understand how it could be missed, but we are told an electrician came.

So my money is on some other item being faulty, with an earth - neutral fault, and the load of the UFH is enough to raise the neutral voltage above earth enough for it to trip the RCD, problem is even turning off all the other MCB's will not help, as the MCB does not isolate, it only turns off the line, the neutral is still connected, as an electrician using a 500 volt mega (sorry insulation tester) it is so easy to unplug all items to ensure you don't damage it with the 500 volt, better to test with 250 volts and leave all connected, but for the householder that must be the first thing, unplug all you can, and switch off any switched FCU's (fused connection units) does it still trip?

 

[Murdochcat]

My money is on a knackered RCD tripping at a low point.

 

[ericmark]

Actually, one thing I do find troublesome with current clamps (of any resolution) is folk using the to measure the current in an earth conductor rather than the residual current in Live conductors, that can be very misleading sometimes

I do check that, I have had it where some earthed items has been drawing current from the DNO supplied earth, and this can cause items like earth rods being eroded. I do not really want to see current in earth wires, or for that matter water pipes or air pipes, there is a problem where I work, two sets of buildings, each supplied from a different step-down transformer, but air pipes link the two sets of buildings, I think a steel 3" pipe would take a fair bit of current before damage is caused, and it is only going to carry current if a PEN is lost, but yes there really should be a non-conducting block somewhere between the two buildings, but putting a clamp meter around the earth cable can alert one of these errors.

Really should not be a PME supply. However, this has nothing to do with the problem here, so we can ignore it.

My money is on a knackered RCD tripping at a low point.

That should have been highlighted when the electrician did his ramp test, however I have seen where swapping a RCD has cured the problem, easy enough for an electrician to swap the two RCD's around to test that out.

Of course, if an electrician did not test it, then we are looking as a different kettle of fish.

 

[Murdochcat]

That should have been highlighted when the electrician did his ramp test, however I have seen where swapping a RCD has cured the problem, easy enough for an electrician to swap the two RCD's around to test that out.

Of course, if an electrician did not test it, then we are looking as a different kettle of fish.

The OP cold do with updating this thread with facts.

When I do this sort of fault finding call out I add such results to the invoice so they are noted.

Too many so called sparks don’t do the important tests or give the details to the customer. Very unsatisfactory

 

[ebee]

When I do this sort of fault finding call out I add such results to the invoice so they are noted.

Too many so called sparks don’t do the important tests or give the details to the customer. Very unsatisfactory

two good points there

 

[Saaj]

I had electric underfloor heating cable and thermostat installed many years ago. It was a loose cable with Heatmiser thermostat. It’s been working fine all these years until September last year when I had issues with it whereby the fuse would trip if I tried to switch-on the the underfloor heating. I recently called an electrician over to take a look and all the cabling from switch to the thermostat was fine and whilst the thermostat was off the wall he tried switching it on and by magic the heating was working fine and it did not cause the fuse the trip. After, about 20 mins of running the heating it was switched off and everything put back together as the electrician had other work to get on with. At the end of the day, he tried switch on the heating using the thermostat and the fuse tripped again. The assumption after some diagnosing was that the thermostat had a fault so it was swapped with the thermostat from another room (this wasn’t a Heatmiser thermostat). This worked for 2 months and now I have exactly the same fault causing the fuse to trip if I switch on the floor heating.

I called the electrician and he is very confused that it worked for 2 months and the same fault re-appeared again. Could it be that this thermostat has also blown?

Are thermostat specific to type of cable or power etc?

I’ve run out of ideas as everything that you can physically see is fine (according to the electrician) and if the heating has worked for two months after replacing the thermostat so it can’t be the cable itself.

Any one come across this or has any pointers or ideas?

Thanks v much

Hi all

Sorry it’s been a while in updating this post.

@ebee @EFLImpudence @ericmark @Murdochcat @mikeyd

Anyway, had an electrician over and he tested the electric cables that provide power to the UFH matt and he also tested the UFH Matt cable.

No issue with the cables that feed power to the Matt but the UFH matt cable was tested to have live and neutral continuity fault.

The issue I have is that the Matt is under tiled floor and I don’t want tiles ripped up to fix the UFH.

I will have to find an alternative way to keep the tile warm during winter. The kitchen itself is is warm enough - UFH was used to shave off the cold during winter and to stop transfer cold

Thx

 

[ericmark]

I have used a Myson fan assisted radiator, but not the plinth type, the kick space heater is made as water and electric heater

and being so low I am told it does heat the floor, but also with the fan it is fast, not sure if it can be used to heat and cool, to cool it needs a pump to remove condensate, but not just if blowing, only if connected to heat pump.

 

[Sajid Patel]

@ericmark Yeah so I am thinking of two plinth heaters and an electric wall heaters towards the end of the kitchen. That should keep the floor warm. It’s a shame the underfloor heater has got a fault as it’s such a blessing during winter to walk on it. I am also contemplating getting someone that specialises in UFH repairs but they aren’t cheap.

 

[ericmark]

My electric under floor heating was a failure, the idea was to have a warm floor in the wet room, and dry the floor so it would not be slippy, One the first attempt the builder damaged the heating mat, so it had to be renewed, lucky the tile cement also faulty, so easy to lift and relay tiles.

But as soon as the shower turned on, the floor would get cold, if we moped the floor ½ hour to dry, if not 2 hours to dry, and the extractor fan moved more air than the floor could heat, lucky also a towel rail, and to heat the room for a morning shower, floor needed turning on before we went to bed.

However, the preparation for the under floor heating worked well, 9" of expanded foam with the plywood on top, stopped any heat being absorbed by the floor, so the wet room floor without the UFH switched on was always warmer than the quarry tiled kitchen floor.

Years ago, the kitchen floor was always quarry tiled, the reason was if the aga needed the fire dropping, there was nothing to catch fire, and also easy to wash the floor and sweep water out of the back door. However, a tiled floor is rather unforgiving if you drop a cup, so in our first house we used cork tiles, could still wash the floor, as varnished, warmer to walk on, and a dropped cup may survive. However, it could also cut a hunk out of the cork, used wood in next house, looked good to start with, but again gets chipped, and a washing machine leak is a nightmare, as goes under the wood.

This house tiled, but carpet on the tiles, and strips of carpet rather than wall to wall, where we walk, and regular renewed as it gets dirty. But the whole idea of our heating is to only heat as required, 14 radiators, 13 heated areas, so we use programmable TRV heads, so rooms only heated when wanted, so the "recovery time" is the buzz word, how long from turning on, to an area getting warm? And the fan assisted radiator reduces the recovery time so much, last house living room had a 4.5 kW gas fire, a 4 kW standard radiator, and a 3.5 kW fan assisted radiator, and from 15ºC to 20ºC (eco to comfort) took 15 minutes, no need for geofencing to pre-warm the room, this house is rather slow to reheat, so eco set to 17ºC, we tried geofencing, and we got rather cold when the EE site when down in high winds, and out heating auto turned down, so we now use simple time, we have 9 programmable TRV heads.

I would think you will find kick space heaters work well, our kitchens are large enough to have space for radiators, and where the doors are, not much else could go in the space, and in a kitchen the fan noise is unlikely to be a problem, our front kitchen the radiator is near to the front door, so we have a TRV head with window open detection, so leave the front door open when unloading car, and heating auto turns off while we unload, back kitchen the radiator too far away from door for that to work.