immersion trips the ELCB.

Turning off the immersion trips the ELCB. Computer fridge etc loses power but not lights. I though ELCB trip would knock out everything?

2011

No. Standard practice for many years has been not RCD protection for lighting circuits although this has changed in recent times.

Furze99

Light circuits are excluded from ELCB in our house - balance of safety concerns. Lights would be handy at night time to exit a house safely. So if a fault developed in say a dryer at night with a risk of fire, the ELCB would be tripping socket and oven/ shower circuits but lights in operation.

OK 2011 and Furze99. I didn't know that thanks. Why would turning off the immersion trip the ELCB? It turns on without problem and heats the water.

2011

https://www.boards.ie/discussion/comment/117673156#Comment_117673156

I will guess: Perhaps the insulation between N and E is not quite what it should be. So under normal conditions a small current flows from L to E but it is below the 30 mA threshold required to trip the RCD. So under these conditions the RCD does not trip. Then the immersion is switched off. Immersion switches are 2 pole. If the N pole breaks before the L pole the neutral current only has one path, through the E. Under these circumstances the current imbalance is large enough to trip the RCD.

https://www.boards.ie/discussion/comment/117674614#Comment_117674614

How would that happen now, been OK for many years. Does insulation deteriorate?

2011

https://www.boards.ie/discussion/comment/117675309#Comment_117675309

Yes, insulation can and does deteriorate over time. Heat is often a factor in this.

Much like bulbs, immersion elements don't last forever. Immersion elements are commonly replaced.

John.G

https://www.boards.ie/discussion/comment/117674614#Comment_117674614

That's interesting, presume no trip occuring when the thermostat switches off the element.

Doolittle51

Might be a dodgy contact on the switch (or timeswitch if you have one?)

John.G

Definitely worth having a look into the isolating switch at least and also at the immersion wiring itself in view of the fact that normal immersion switching is done by the thermostat switching only the neutral and this isn't tripping the RCBO/RCD.

2011

Simple for an electrician to fix. I would start with an insulation resistance test.

I very much doubt that this issue is due to an issue with the time clock or isolator. It is most likely due to an insulation failure within the immersion element. This is very common.

John.G

Should it not also trip then during normal use? and not apparently only when the main switch is switched OFF.

Bruthal.

https://www.boards.ie/discussion/comment/117700346#Comment_117700346

If it was being caused by 2011s theory, then the stat should cause the same thing when it switches, if it is switching the neutral, and if the fault is not between the stat and isolator, (in which case the stat would be switching out the fault).

i tried an experiment. I switch it on and there is no problem. Then i turned off the immersion fuse at the fusebox before switching it off. Then turn on the immersion fuse at the box again. It does not reip. Does that tell anything?

John.G

Not a awful lot as you don't know if the immersion was actually heating the water at the time or not and you also don't know if the immersion is/was heating the water or not when tripping the RCD when switching off the on/off switch.

I would suggest switching it off at the fusebox and open the on/off switch and check for any signs of damage inside and check all terminal screws are tight (post photo if possible).

I presume that when the immersion is on normally that it is heating the water to its normal temperature and then cutting out on its thermostat, in other words if you leave the immersion on for say 12 hours and are drawing hot water off that it appears to work quite normally?

John.G

Should also have said that the next time it trips when you switch off the On/Off switch; immediately switch it back on and reset the RCD and then switch off at the fuse box, that might tell something.

https://www.boards.ie/discussion/comment/117712867#Comment_117712867

I presume that when the immersion is on normally that it is heating the water to its normal temperature and then cutting out on its thermostat, in other words if you leave the immersion on for say 12 hours and are drawing hot water off that it appears to work quite normally?

Sorry do not understand. i would never leave immersion on 12 hours. It heats the water very quicky. How would i know if it was cutting out on its thermostat? I will try looking at the switch with the power off at fusebox

I have noticed that after it has been turned off at the immersion in fusebox and then turne don it doesn't trip for a couple of times when switching off

John.G

If the thermostat is not switching off the immersion then the water will boil and you will hear it apart from scalding hot water coming from the hot tap, I certainly don't think there is any problem there but I don't know if you are leaving the immersion on long enough for the water to reach its normal temperature of 60C to enable the thermostat to operate.

I think the trip switch is only operating if you switch off the on/off switch while the thermostat/heating element is calling for heating even though it shouldn't trip under any circumstances when you do switch it.

I would inspect the switch first and then suggest the following.

Switch immersion off and keep draining off water from a hot tap until it is only warm, c/o to the "Sink" element if this is not already selected and switch on the immersion, do not use any hot water for 45 minutes, the thermostat should then have operated, check to see if the trip switch has operated, if not switch off the on/off switch and see does this now trips the trip switch.

https://www.boards.ie/discussion/comment/117714993#Comment_117714993

Thanks. I turned off the fuse and opened the switch. But the wires are folded and i was afraid to stretch them in case i would break where they are connected to the switch. So I could not get enough space to see much or take a useful photo.

I never hear water boiling but it heats a bath very hot in a short time, sorry never actually timed it and i know short times is as short as a piece of string😀. The switch is always at sink.

I will do as you suggest in your last para and report back

OK with just warm water in tap\sink element selected\ no hot water used\ i turned on immersion from the immersion switch.

it tripped the ELCB in 30 mins. I did not get to 45. It is the first time it tripped without being turned off. Water is very hot cannot hold hand under tap

John.G

It reached 60C or whatever its set to I would think and then tripped when the thermostat opened, 30/35 minutes would be correct for heating this amount of water, I would think that the reason that its only tripping occasionally when you switch off is that it is still heating up and the thermostat hasn't reached opening temperature. It looks, as others suggested that the element is breaking down and tripping the ELCB as it heats up but without at least looking at the on/off switch wiring and the immersion top wiring; couldn't be 100% sure. You can do this yourself with power off, if you ignore it and the element is damaged then it will eventually just trip as soon as its switched on which is no use as your fridge etc is on the same ELCB.

If you are still a bit dubious about stretching the wires in the on/off switch I would still remove the immersion top (power off) and have a look and see what the thermostat is set to and look for any signs of burning/arcing anywhere.

https://www.boards.ie/discussion/comment/117716982#Comment_117716982

Ok thanks I will try tomorrow. From my limited view of the switch there was no burning anyway

John.G

https://www.boards.ie/discussion/comment/117674614#Comment_117674614

https://www.boards.ie/discussion/comment/117674614#Comment_117674614

I have seen a few posts on different sites where it quotes RCDs tripping on apparently perfect systems including immersions due to the negative pole (or any pole) opening first when the isolating switch is turned off and the resulting arc then causes some imbalance or other in the RCD coils and trips it. If this is correct then one might expect the same to happen, even occasionally, when the thermostat opens, this always breaks the negative on top mounted dual immersions with live still on the element, (both elements are then live via the shorting link)

2011

https://www.boards.ie/discussion/comment/117721481#Comment_117721481

You have misread my post, in it I state "Perhaps the insulation between N and E is not quite what it should be."

This is quite differnt to the "apparently perfect system" that you describe in your post.

What I described above was a guess at what may be causing the RCD to trip under fault conditions when the switch is operated i.e. only when the insualtion has failed to some extent.

This would not cause the RCD to trip if the circuit (including the element) was healthy.

It should also be noted that no double pole switches opens or closes both poles at exactly the same time. This simply is not possible.

Antenna

https://www.boards.ie/discussion/comment/117721481#Comment_117721481

You mean Neutral not negative, it being AC not DC :)

THere are modern immersions where the thermostat switches the Live (using two thermostats for both elements), not the Neutral as in the past

This to increase safety as I think there was some incident in England where the neutral end inside an immersion broke loose? and came in contact with earth. The earth completed the circuit so the immersion kept boiling away without being cutout by the thermostat which was on the N. Obviously if an RCD was present for the immersion it would have cut out straight away with large current flowing on the earth.

John.G

Yes, neutral, not negative.

Havn't heard of twin themostats with live switching in a dual immersion but all dual immersions now have either a hi limit stat incorporated in the control stat or a surface mounted hi limit stat wired in series with the control stat.

I have a 49 year (Santon, cost 7 punts in 1972) old twin immersion, only 3 wire with the sink/bath c/o switch not very conveniently mounted on top of the immersion itself, I have only always used the sink element, it has no safety stat but I have it wired through a 30 minute mechanical timer so should help to limit boil over time in the event of stat failure.