RCCB tripping randomly
- Thread starter StephenB
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Now that is a question I don't have an answer for.
There doesn't seem to be any exact timings as to when any fridge or freezer will attempt to defrost, the same unit can vary from 36 - 48 hours going up to 7 - 10 days
The only reason I discovered the defrost element issue was after narrowing down the tripping faults on a job to a freezer, the customer was all set to bin it so I asked if they would let me have it to see if I could find what was causing it trip their RCD, having got it in the workshop I took a cover off the back and found a mechanical timing relay, testing the output I found a short to earth and followed the wiring to a faulty heating element which at the time around 30 years ago cost about £8.50. The customer hadn't replaced the freezer so they got it back repaired and I got paid for the repair so it was a good result
Since then I've found probably a couple of dozen fridges / freezers that have a faulty defrost element without spending many hours looking for the intermittent tripping fault
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Sharpend
"It Just Is"
Could you not cause it to freeze/defrost by leaning the door open for a while?
or would this take several hours b which time the food would be no good anyhow?
or would this take several hours b which time the food would be no good anyhow?
Using one takes seconds and then you can see how close the leakage is to the RCD threshold ......... you're unlikely to find a fault using one but I find it helps rule in or out accumulative leakage in the initial tests
Sharpend
"It Just Is"
Agree with that Murdoch, it does help eliminate a few potential issues.
and? your post still implies that you need one to find a fault and that anyone without one isnt capacble of finding a fault...
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I have one BUT I managed decades without one. Megger Mark had them on silly offer so,I had to have one 
Its handy when needed, the rest of the time it just takes up space
Its handy when needed, the rest of the time it just takes up space
fact you say 'check they have an earth leakage clamp meter' implies that they must have one and anyone without shouldnt be getting the job. fairly black and white, and far clearer your intentions that many of the regs in BS7671
Sharpend
"It Just Is"
Well I read ‘fairly black and white’ as equality, but then the sentence didn’t make much sense 
msl1:
msl1:
or reading this.
I've often said that we need to send a copy of BS7671 to the Plain English Society - for their comments!
Maybe I'll start by sending them a copy of 18th Ed AMD 1 - because it seems very few people under it
Thanks everybody for all your tips and suggestions. As I don't have access to any specialist equipment or the knowledge to interpret the readings, and there's no guarantee the fault will recur if I were to hire the kit or get an electrician in, I need to narrow down the possible causes before I call in an expert, so I've come up with a plan and I'd appreciate your comments. There's a spur from the upstairs power circuit that feeds the new boiler and immersion heater in what used to be the coal shed plus an outside double socket. Then it goes under the path to the garage where it feeds a double socket, a light and an outside double switch, one of which serves an outside light on the garage and the other serves two outside lights on the sheds. The spur continues under another path to a long shed that's divided into three sections, each of which has a double socket and a light. The feed from the second outdoor switch passes under the path, through the first two sheds to the third one where there are two outdoor lights. Given your comments about water and outdoor light fittings I think the problem is most likely somewhere on this spur, so my plan is to try to isolate the spur. I have found a two way RCBO "garage" consumer unit from Consumer Unit World so I thought I would fit this in the boiler room to protect all the outdoor connections. The idea is that if the main RCD trips again the fault is likely in the house, whereas if the RCBO in the boiler room trips it would confirm that the problem is outside. My worry is that if there's 1mA of leakage inside the house it would only take another 29mA outside to trip the RCD in the main consumer unit in the house, whereas it needs 30mA to trip the RCBO in the boiler room. Any comments? Thanks
You clearly don't understand how RCDs work - what you are suggesting could easily be waste of money IMHO.
If the 2nd RCD is down stream of the 1st, the 1st will have an amount of earth leakage on it already so will almost certainly trip before the other one.
Post 2 more times then upload a picture of your fuseboard is the best suggestion I can make
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No.. Your logic is wrong..
First if you were going to fit any consumer unit that includes RCDs / RCBO's...
Then to do it correctly you need the test equipment, (that you say you haven't got and that you don't know how to use), in order to verify that your alteration is safe to use before you re-energise the power to the circuit...
It is not Specialist Equipment .. it is basic equipment to do any electrical alteration work safely.
And... if you have a circuit with one RCD supplying another RCD further down the circuit and you get a fault at the far end of the circuit. it is pot luck around which RCD trips first or not..
i.e. a fault on the outside wiring with your scenario could give ANY of the following symptoms.
1/ Original RCD in house trips on its own.
2/ New RCBO board trips on its own.
3/ Both RCD in house and new RCBO boards tip together...
So a fault outside could give you results that prove absolutely nothing about where the cause is..
:shakehead
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Just to add some other points your should be aware of:-
1/ You are correct that an intermittent fault is unlikely to occur while you are doing any testing...
BUT doing testing you can eliminate some items from the probable cause..
i.e. you can verify that the RCD is NOT oversensitive...
or, you can verify if the insulation resistance of the circuit cables is good, reasonable, or slightly suspect. etc..
2/ Anyone who has done any fault finding will know full well a couple of golden rules:
(a) Assume everything is faulty, until you have proved otherwise.
(b) Faults may be due to multiple causes combined, not a single event.
So irrespective of what you think you may have tested, or proved...
If I were asked to come and investigate your problem as paid work,
I would still go through my standard routine of procedures to verify everything is correct as per BS7671,
in order to diagnose possible causes..
and unless you could show me your test results and the calibrated test meter you used to obtain them then I would probably ignore anything that you thought you had proved.
Your intentions and enthusiasm are good...
But without suitable test equipment..
Randomly swapping parts can be a very expensive waste of time and money compared to getting it done correctly..
Bit like pi55ing in the wind... you may hit the target... but you are more likely to just ruin a good pair of trousers!!
Guinness
You started by expressing a fear of "cowboy electricians". To be honest reading the description of your outdoor "spur", it seems to me they have already been there.
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I suspect the result of many "cowboy boy" works is the customer selecting the cheapest person, who rushes the job, cuts corners and doesn't test properly, nor knows how to diagnose faults properly ....................
Then of course there are the "handymen" or "builders" doing this work with little or no knowledge or test kit.....
It certainly looks that way from the fact that there's so much hanging on one MCB. We bought the house in 2018 so most of it was done by the previous owners, who did leave us lots of paperwork. The kitchen was fitted in 2010 by a firm of kitchen fitters and the owners left us a NicEic Domestic Electrical Installation Certificate that details the work as : Changed fuse board, upgraded main earth bonds, relocated sockets and cooker and lights in kitchen. I don't think they were trying to do things on the cheap. £25,800 was a lot of money for a kitchen in 2010. There's one socket behind the door, where they didn't fit any new units, that's on the downstairs sockets MCB and the cooker box has its own MCB. These are both on the first RCD. All the other sockets in the kitchen and the strip lights under the wall units, are on the upstairs sockets MCB, which is on the second RCD. Presumably it was easier to get to the upstairs circuit through the ceiling than it would have been to use the downstairs circuit from under the floor. The garage and sheds were rewired in 2013 and they left us a Minor Electrical Works Certificate for a Domestic Installation. The supply to the garage is taken from the back of a socket in the kitchen, through what had been the old coal shed and then under ground to the garage etc. so it's all on the same upstairs sockets MCB as the kitchen and hence the second RCD. Shortly after we moved in the boiler packed up. We didn't have the option to go for the cheapest as it would have left us without heating or hot water, possibly for weeks, so we stuck with the plumber who was fitting a new en-suite shower room for us. I don't like combi boilers so I asked him to fit a new boiler with a mains pressure hot water tank. There wasn't room for this in the kitchen, where the old boiler was, so we decided to put it in the old coal shed. This entailed some work on the roof to make it water-tight. As the power to the garage already passed through the old coal shed the electrician who worked with the plumber connected the boiler and immersion heater to the same supply, i.e. the upstairs sockets, kitchen, garage and sheds MCB on the second RCD. He also supplied a minor works certificate. So all the tests were done in 2010, 2013 and 2018 and all passed. Personally I would never have hung all those sockets, lights and boiler off the one MCB, but these guys were supposed to be professional electricians with all the appropriate qualifications and test equipment, so who am I to question what they did?
I'm a bit daunted by the thought of trying to find what's tripping the RCD myself, but I'm left wondering how do I find an electrician I can trust to do it for me?
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