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Thread: Frustrating, intermittent earth fault

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    Frustrating, intermittent earth fault

    I have a problem on which I have been stuck for the past three weeks. One of my clients have been experiencing earth leakage trips intermittently since the beginning of April. It all started when their gardener washed the walls of their home. I investigated and found that the problem initially "wandered" between circuits, in other words, the earth leakage unit would trip and would not reset until you switch off "Plugs circuit breaker 5" for instance. The next time it trips, it would reset only once you switch off circuit breaker 7.

    I disconnected all the neutral conductors and carried out an insulation resistance test on all of the circuits/cables. Initially, I picked up a fault (24kΩ) on one of the cables between Live and Earth. I disconnected this cable completely and all the other cables tested clear (>600MΩ).

    The problem did not subside however and rather seems to have stabilised to one circuit, feeding 3 plugs and 3 lights, all located in one room. The reason why I say this, is that when the earth leakage trips, it won't reset until they switch this specific circuit breaker off. I have tested the circuit a number of times and it tests clear, yet every time it starts to rain, the earth leakage trips. I though it would be a fruitful exercise to simulate rain by spraying the area where the cables run with a hose pipe and yet nothing happens. I have opened every socket outlet, light and junction box to assess for water ingress, yet everything is dry.

    I have replaced the earth leakage unit twice. It trips at 25mA with all the circuit breakers switched off and as I switch them on, the sensitivity gradually decreases until it finally reaches a tripping current of 6mA with all circuit breakers switched on. At this point I can't even plug my earth leakage tester into the socket outlets and it trips the earth leakage. There are 14 circuit breakers connected to this earth leakage unit.


    This fault is driving me insane! Is there anyone who has had a similar experience and could shed some light on this for me, please?

    Thanks.

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    install a separate earth leakage relay just for that one circuit. it will make it easier to find the fault. sometimes the accumulative slight earth faults on each circuit add up to over the tripping value.

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    Bronze Member ACEsterhuizen's Avatar
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    Been there done that, and truthfully, these guys really, really, helped me a lot. But they are not cheap. - And of course what Bergie said.

    One (of many) solutions is of course that elusive and perplexing process of elimination.

    I, once, (this year) rewired a complete plug circuit because I failed to notice a back to back plug, enclosed by a built in cupboard, and a faulty multiplug plugged into that, used by rats to urinate on, causing the EL to trip when it went to pee.

    Invest in one of these (tnx andy) if you have not already, if correctly used, it is (supposed to) to identify and/or measure any difference in milliamps between L&N (which causes the EL to trip) This way you can actually see the milliamps increasing/adding up as you connect/test (L&N&E) different circuits (if there is lots of small leakages adding up to 25 or 30 or whatever rated Ma which then trips the EL) - (LN fault=trip, LE fault=trip, NE fault=Trip)- (EL Load side)

    All that said, it takes time to find these ghosts in the machines, and, or rather BUT, the customer are rarely willing to pay if you spend 8, 16, 32 hours to look for such a fault.

    That is why, when I get to (or just before) these type of "madnesses", I rewire the whole circuit. Easier on the budget and for my sanity. But boy do you feel like an ass when you're done and find that hidden rat pee'd on the hidden multiplug, plugged in to the "close up" wall plug.

    PS. a "faulty" "Neutral to Earth" fault can also trip an E/L. (disconnecting the L only to test E/L issues means a 50% test) = TEST the COMPLETE "electrically separated circuit".
    Last edited by ACEsterhuizen; 27-Apr-17 at 07:16 PM. Reason: more info

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    Diamond Member AndyD's Avatar
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    A 24kΩ L-E reading is pretty low although on its own it wouldn't cause nuisance tripping, what tester did you use when you took the measurement? Did you investigate and fix the fault? What was causing it?

    It trips at 25mA with all the circuit breakers switched off and as I switch them on, the sensitivity gradually decreases until it finally reaches a tripping current of 6mA with all circuit breakers switched on.
    What tester are you using to measure the leakage current?

    If you're now on your 3rd earth leakage breaker and the problem was identical with each of them then it's reasonable to assume the earth leakage breaker itself isn't the problem. Just for future, for the price of three earth leakage units you could have bought a proper RCD ramp tester and proved conclusively if they were faulty before replacing them.

    Is the tripping problem happening every time it rains or just some of the times? Does it ever trip when it's not raining? How often is it actually tripping ie is it every day, every week or once every month / in a blue moon? If it's every day or at least twice a week you could maybe disconnect the suspect circuit for a few days and see if the tripping problem disappears before you take the plunge and rewire it.

    Have you investigated all the appliances that the customer might be plugging into the sockets? I'd suggest testing every appliance again for insulation faults with a mega tester using 500v tests preferably or 250v tests where it's appropriate and make sure they declare all appliances including the 3-speed massager that's hidden away at the back of the wardrobe.

    In the past I've known rodent damage to cause the type of fault you describe where mice have stripped away insulation at random places along the wiring. The only way you find these kinds of faults is by methodically following the circuit and visually checking in all places possible.
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    Diamond Member AndyD's Avatar
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    I've had an earth leakage tripping problem at my own house for about 2 years.....yeah, you can smile. It was only tripping about once a month and it was one of those minor annoyances I never quite got around to investigating. It was also completely random, every time it tripped I made a mental note of which appliances were running and whether it was raining etc etc and there was no pattern whatsoever.

    Anyway needless to say, over time it the tripping got more frequent and eventually it was tripping every week so I decided to fix it. I started by ramp testing the earth leakage breaker (RCD) which passed with flying colours. Same as you I identified all the neutrals and I IR tested all circuits with a mega tester one by one, none of the readings were less than 50MΩ @ 1000V. I mega tested every single appliance (including the 3-speed massager in the back of the wardrobe )....nothing.

    Eventually I left my earth leakage clamp meter around the L+N that supplied the RCD and left it on 'max hold' for over a week to record the maximum leakage over that time. It showed 9mA as being the max leakage and during the test period the RCD tripped twice. I ramp tested the RCD multiple times again and each time it passed.

    None of the evidence added up to anything, still no pattern to the tripping, appliances all tested good, all final circuits tested good, RCD consistently passed every test I could throw at it and no leakage fault I could see over time with a clamp meter that would result in a valid trip. Eventually I did what I usually advise people not to do and replaced the RCD even though it tested fine. I bought a good brand name and ramp tested it several times before I fitted it, that was 4 months ago and to this day I've never had another nuisance trip. Go figure....I still don't know why the old RCD was tripping.
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    When I am not sure of which circuit is tripping the RCD I usually wire up a seperate DB board a have made for this purpose.
    Its basically just a board with a bunch of earth leakages (RCBOs would be better), I supply my sub test board with a mains supply non rcd protected and give each circuit its own EL, i have the earth leakages numbered and ask the client to make a note of which tripped.
    Once I know the circuit I check every nook and cranny of that circuit.
    I have on more than one occasion found a socket needed changing although I could not pick up on the fault by testing.
    I'm not sure if they are available but I have a new easier idea to test clients appliances cause they never listen when I ask them to unplug an appliance to help the process of elimination. I plan to buy an RCD with a 10ma tripping current or close thereto and wire a plug top and socket to it, then clients can plug their appliances in and tell me if it trips over night etc ( this RCD should trip before the main RCD).
    ... but clients never want to hear its the appliance fault lol they would rather lie and get me to come have a look and pay more than buy a new kettle x)

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