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Thread: earth leakage tripping

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    earth leakage tripping

    I am sure you have all heard this before

    Anyway, i had an issue with a property were the earth leakage would trip for no reason, randomly. But more often when the garden lights were being used, So i had to put on my thinking cap and actually go do some work.

    One of those jobs. I tested all the cables and lights made sure everything was clear then left. That night my phone rang, earth leakage tripped again.

    I stripped the entire garden light circuit, removed all the lamps and tested again, all clear over 10 Meg. I disconnected the garden lights from the main (house) earth leakage and fitted an earth leakage unit next to the switch as a temp measure.

    Then i did mA leakage readings, first on the earth and then across live and neutral. The leakage on the earth wire was so little it wasnt worth wasting time on it. However the live and neutral leakage was 14.6 mA on the main DB without anything switched on and 5.6 mA when testing the garden lights. So what i assume was happening is the mA added together plus leakage current once other devices were switched on exceeded the threshold of the earth leakage. the highest leakage recorded was traced back to an element in the stove disconnected and bingo problem solved. No more earth leakage tripping for now. The earth leakage is an old unit which trips at around 20 mA when I recorded tests with the earth leakage plug test.

    Normally when i do domestic fault finding I dont really pay much attention because it is such basic stuff, but every now and again you get one of these interesting faults which test you.

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    Diamond Member AndyD's Avatar
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    Glad you got it sorted out. There's no feeling quite like it when success comes eventually after the application of your knowledge and experiance and a lot of hard work.

    This is a classic example of fault finding. Firstly your tester can only show you so much. If a problem is intermittant and persistant then there's no substitute for getting down and dirty and exposing all the connections and termination points and visually check the entire circuit from start to finish. Sometimes you can see the problem with your eyes but not with a tester.

    Secondly with earth leakage faults the circuit that actually causes the tripping isn't always the circuit with the biggest insulation fault. In contrast to my point above in this case there's no substitute for the correct test equipment and knowing how to use it. I've seen on several occasions where someone has put a clamp tester around the CPC (earth wire) and assumed that there was no fault because there was only a very small current registered but with no regard for parallel paths where other, often larger, earth currents are flowing.

    I think to find some of the more obscure or intermittant RCD tripping faults you need each of the following in pretty equal measure;
    1. Correct test equipment.
    2. Good knowledge of your testers, testing proceedures and the distribution network & final circuits you're working on.
    3. Not scared to work or take step ladders off bakkie or sweat profusely or get hands dirty.
    4. Be anal, methodical, analytical and persistant and generally like a dog with a bone.
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    Bronze Member ACEsterhuizen's Avatar
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    Staying within the relevant thread did anyone had first hand experience with this meter ? Any other meter (except over priced & over rated flukes) that could be recommended? Thanks in advance.
    Last edited by ACEsterhuizen; 07-Nov-14 at 06:22 AM. Reason: colour

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    Diamond Member AndyD's Avatar
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    I have one and I use it as a backup tester. It works well and does what it's supposed to. I also have one of these which is the same as this one (rebranded) which is on the Test Meter website. I actually have 2 of them because they were on a offer for <60 when I bought them.

    I use the di-log one for everyday use because I prefer it, it seems to have a higher sample rate which gives better results when using the 'peak hold' feature but it's swings and roundabouts because the Kew tester has a larger diameter clamp which is handy because you often need to clamp two wires simultaneously.

    Another tester I have that can measure down to 1mA accurately is this one. I like Chauvin Arnoux testers a lot, as a brand I hold them in high regard. It's not marketed as an earth leakage clamp meter but it's ability to maesure 1mA makes it a contender anyway and there's lots of advantages with this one, firstly it uses a flexible clamp that unclips entirely at one end so it's easy to thread it around the wires you need even if they're inaccessible. Secondly it's RMS and it's got good accuracy. Thirdly it's a 45mm clamp so it's bigger than most earth leakage clamps and there's also a version of the same tester available for an extra hundred bucks that has a massive 70mm flexible clamp. Finally it's available at a good price from RS Components who'll deliver to your door in SA so you don't have to worry about customs and excise whacking you with import tax etc and you don't need to persuade a buddy to smuggle it over for you in his underwear when he's coming here on holiday from the UK .
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    Following on with ians original thread, I had a similar situation the other day. For some or other reason the office lights at our mine are supplied through an earth leakage relay.
    These lights are all fluorescent 5 foots. Usually a CB will feed several fittings. Luckily this only was only feeding five.

    What is the best way to test such lighting systems, as I see if you test the ballast to earth, all are down? Do you just start at a point and work towards the faulty light or is there an easier way to do it. From what I've seen in recent posts, you guys have years of experience and know what you are talking about.

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    I look after a few medium size supermarkets and boy are those rows of lights a mission especially when the middle or last one in a circuit pops. Now what i do is scan the fittings with my thermal imager prior to there being any faults. I then upload the images and record and take note of the higher temperatures. It makes my life a whole lot easier.

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    Diamond Member AndyD's Avatar
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    Quote Originally Posted by gobbleteller View Post
    ....What is the best way to test such lighting systems, as I see if you test the ballast to earth, all are down? .....
    If you test a fluorescent fitting that has an electronic ballast then firstly you need to disconnect the live and neutral of the supply, if you leave the neutral connected then you'll probably be seeing the neutral-earth bond on the supply side. Also electronic ballasts usually have surge arrestors built into them so you need to use a 250v test and not any higher otherwise the MOV's start conducting to earth and look like an insulation fault to the tester.
    .
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    Bronze Member ACEsterhuizen's Avatar
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    Thanks Andy, bought and delivered this one. It is surprising small, i mean tiny :-). Now to figure out the correct way to use it, the instruction manual's english is french to me. :-)

    I clamp around live and neutral at bottom of earth leakage. In theory it should read 0 amps if there is no leak somewhere? So it will show the sum of all leaks in the system under the RCD, thus if it shows a leak i can start eliminating circuits to find the culprit?

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    Diamond Member AndyD's Avatar
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    Congratulations on getting your new tester, I still get excited when I get one. Yes they are small but I've only found that to be an advantage and obviously the flexible clamp means you can get it into places a normal clamp meter won't go unless you start rearranging the wiring. I doubt the instructions will give you info on actually finding faults but I'll dig out mine later if I have time and have a look.

    If you clamp the L+N either above or below the RCD it will show you the global leakage of all the circuits it's supplying as a live test. Obviously if it's a 3-phase RCD you need to clamp around all 3 phases plus the neutral simultaneously. You can get a very good indication of the leakage on individual circuits by switching them off one at a time and seeing how much the global leakage alters for each circuit.

    This tester isn't as accurate as some of the earth leakage clamp meters which have a resolution down to 0.1mA or even 0.01 mA but TBH I've never seen the need to be that 'accurate' for normal RCD tripping faults, when there's at least 25mA current being lost somewhere 1mA resolution is more than adequate for localising the problem and also accurate enought to pick up a trend of substantial increase or decrease of leakage current over time. I've always found it to be a damn good tester and I'm sure you won't regret buying one.
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  12. #10
    Diamond Member AndyD's Avatar
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    Thought this was worth a bump, I wondered how you were getting on with the new clamp meter, I'm sure you will have given some good usage by now.
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