RCD Tripping

[sinaloan]

Hey Guys,

I got called out to a house today on my way home where the tenants got a problem with the rcd randomly tripping. When i got there the rcd was fine and wasnt tripping. she said that it happens in the morning when the heating switches on, some days it does it and some days it doesnt. on days that it does do it in the morning it trips throughout the day also.

the heating circuit is connected to the kitchen ring. basically when it does trip and she cant turn the rcd back on she turns the heating spur off and the rcd turns back on. she said this has been happening for about two years now (since she had the fuseboard changed with the rcd added and work done in the kitchen) and she has had quite a few people round to look at it electricians heating engineers etc to fix it and noone has managed to.

Whilst i was there i did a insulation resistance test on the kitchen ring with the heating disconnected and everything came back great <200, i also did an rcd test and this was okay too.

In the kitchen there is a programmer for the heating, in the lounge there is a thermostat, in the downstairs outside cupboard there is the boiler with a stat above it which im assuming is a frost stat?

Upstairs there is the cylinder, they have replaced the valve as this is what a previous electrician said is wrong with it and still the same problem happens.

Basically I have only a small amount of experience wiring heating systems and so Im slightly unsure where to start to find this fault. I think its a y plan system as there is only one valve???

any help would be greatly appreciated guys

 

[Richard Burns]

Very difficult to identify an intermittent fault. may be worth ramp testing the RCD, if you did not do this, to check it is not tripping at 16mA.
Since the customer had identified that switching off the heating spur clears the fault, this does indicate that the problem is with the heating circuit only (unless it is a build up of earth leakage from all circuits, might be worth checking).
If the spur is a single pole switch not double pole then the problem is line to earth, if double pole could be either.

Therefore concentrate on the heating circuit (without the ring) and since the problem occurs when the heating switches on then it is not a problem with something heating up and then failing it is a direct fault with wiring/equipment.
Initially check the routing of the wiring and see if you can identify any likely damage points, accessories, going under floors, through doorways, cables unsupported, etc. If there are no signs of damage, then break the heating circuit down into units and test the cable for each section. If you are lucky an IR test of the cable (without sensitive items attached may show the problem. If there is nothing then move on to the equipment.
Good luck.

 

[Jabbajaws]

I have also come across a similar problem, which turned out to be a neutral that had been 'borrowed' for another circuit from an immersion heater circuit.

Everytime the immersion kicked in, the rcd tripped...

 

[fulla]

had a similar problem tuned out to be a cable in the motorised valve touching down as the valve opened.
good luck

 

[PC Electrics]

First check if the spur is SP or DP. If SP then suspect a L-E fault. IR test all Ls to E from the wiring centre with your tester on 250V without disconnecting anything. Make sure you test all cables. If you find a fault then use the standard wiring diagram (and eyes and continuity tester) to determine what equipment that terminal feeds. Disconnect and retest each piece individually. Move your tester up to 500V only when you can be sure you're not connecting to anything electronic.

Also check the wiring centre over very carefully for any stray fine wires which might be shorting.

Chances are it's wiring, boiler, 3pv or pump, usually everything else is class 2 and has no earth connection (check this though as it does vary according to make).
I've previously found a gas valve that was shorting to earth only when energised - so when dead no fault could be found. So if you cannot find any faults in the rest of the sytem you might find yourself carrying out some "empirical" testing on the boiler.

BTW if the RFC is reading <200 (I assume this is Mohms?), then what is the actual reading? or do you mean >200 Mohm

Empirical evidence would suggest this is a tricky problem to resolve (but this is by no means certain as previous efforts may have been numpties).

 

[sinaloan]

Thanks guys your help is greatly appreciated. Judging by what the previous electricians did it doesnt seem like they did alot. No ins res test or checking of any wiring, advising to take off of the rcd side, blaming other trades etc etc. I am certian that the fault is within the heating but I will do the ramp test on the rcd just to check. also there isnt an actual wiring centre basically all of the cables meet in a single dry wall box with a blank plate over it and are just connected with connector strip its a complete mess. I think what ill do is disconnect everything and start over again from scratch wiring into a proper wiring centre and checking the ins res of every cable. sorry pc i meant >200 megohms. i think this ones gonna be fun haha

 

[kenny james]

i have come across this a few times and probably the other sparks have too!, such an annoying fault as explained above by other comments it can be a number of things and unfortunately if you have done all your tests and all have come back ok the fault then becomes a problem for the gas engineer instead not you, various things i have done to cure the faults and which have rectified the tripping i have replaced the spur switch to a double pole instead of a single pole, called the gas engineer in who found the fault to be the pump within the system, tends to also be an earth leakage fault, if the circuit was on its own dedicated cct i would wire onto the non rcd side of the board, you said it was wired into the ring main socket?, i would recommend that you keep the socket rcd protected.

 

[La Poste]

How about RCBO'ing just the ring main, at least that will make the nuisance tripping less of a nuisance as only one circuit will trip out.

 

[sinaloan]

Thanks but how would changing from a single pole to double pole switch benefit? The switch will always be on right..........

 

[li150pacemaker]

I was called to an almost identical fault recently and found it to be one of the motor supply cables within the 2 port zone valve was trapped by the zone valve metal cover/lid and was just touching a copper pipe running just below it! It was difficult to find due to the valves position amongst the pipework.

 

[sinaloan]

Hey guys,

I went back to this job at the beginning of last week after studying heating plans and armed with my y plan diagram. basically i completely unwired everything checked every cable for damage (a couple of cables were slightly damaged) replaced the damaged cables and rewired the entire thing. I also found that the frost stat was wired into the wrong terminal (8 instead of 5 if i remember correctly) i then checked all of the components in the system for loose cables or damage (which i found none). It makes sence that it was the frost stat as it was only happening on some days (cold ones) and on those days sometimes it would last all day (when the frost stat was kicking in and the temp was cold outside probably all day) Everything has been completely fine since and I recieved a brilliant review from the customer and got more work from this from her recommendation.

Just wanted to say a massive thanks for everyones input and all the advise and help i recieved

cheers lads :smile5:

 

[Heisenberg]

Hey guys,

I went back to this job at the beginning of last week after studying heating plans and armed with my y plan diagram. basically i completely unwired everything checked every cable for damage (a couple of cables were slightly damaged) replaced the damaged cables and rewired the entire thing. I also found that the frost stat was wired into the wrong terminal (8 instead of 5 if i remember correctly) i then checked all of the components in the system for loose cables or damage (which i found none). It makes sence that it was the frost stat as it was only happening on some days (cold ones) and on those days sometimes it would last all day (when the frost stat was kicking in and the temp was cold outside probably all day) Everything has been completely fine since and I recieved a brilliant review from the customer and got more work from this from her recommendation.

Just wanted to say a massive thanks for everyones input and all the advise and help i recieved

cheers lads :smile5:

Thanks for taking the trouble to come back and tell us the outcome. Certainly one to note and store away for future reference :smart: