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Thread: One of the weirdest faults I have found

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    One of the weirdest faults I have found

    Friend of mine mentions that the place he is staying in has a earth leakage that he thinks is not working right. So I am there but have no tools and he at least has a semi decent multi meter. I press the test button as he has done and it trips. Reset it and try again - nothing. Ok. Easiest way to test earth leakage undo everything at the bottom and take a piece of wire and touch from neutral to earth. Doesn’t trip but creates a small arc. I think to myself ok thats not right. Take the multimeter and test. I get the full 230v between the neutral and earth after the earth leakage but before the earth leakage its round about 10v. Not knowing if his tester is ok or not I get a normal cfl bulb and touch one point to the metal casing and the other one to my wire. It lights up but flickers. I then disconnect the neutral at the top of the earth leakage and connect a wire from the earth bar to the top of the earth leakage and do the same touching the cable from the bottom (which now should be a earth) to the one point of the lamp and the other point to the metal of the db which i did check was connected to the earth bar. It lit up ! What is going on here ? How can I get a voltage thats strong enough to light up a lamp between earth and earth by just passing it trough the earth leakage ? I reconnected everything as I found and told him to be very careful until I can have a decent look at just what is causing this strange fault.

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    Diamond Member Justloadit's Avatar
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    I have had a similar situation, but not with earth leakage, but a three phase motor starter and screw on overload, the type where you have to screw the overload to the base plate, as it was a large contactor & overload.

    There was a small current flowing between the phases and earth, not through the contactor, but through the overload.
    Not sure the reason this was occurring, but took a while to figure out. Once I replaced the overload, problem went away.
    I must say that I never broke open the overload, too busy at the time to inspect.

    There could be a number of explanations.
    This was on a golf course who are always watering the turf using sprinklers, so humidity could have gotten into the DB board, and finally settled with in the Overload enclosure.
    There could have been insects with in the overload, which eventual got electrocuted and remained in the position causing a carbon track. Seen a number of these on PCBs I repaired.
    There could have been overload trips over time, which created a carbon path, which eventually lead to the base and earth.
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    Diamond Member AndyD's Avatar
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    Quote Originally Posted by JustJohann View Post
    Friend of mine mentions that the place he is staying in has a earth leakage that he thinks is not working right. So I am there but have no tools and he at least has a semi decent multi meter. I press the test button as he has done and it trips. Reset it and try again - nothing. Ok. Easiest way to test earth leakage undo everything at the bottom and take a piece of wire and touch from neutral to earth. Doesn’t trip but creates a small arc. I think to myself ok thats not right. Take the multimeter and test. I get the full 230v between the neutral and earth after the earth leakage but before the earth leakage its round about 10v. Not knowing if his tester is ok or not I get a normal cfl bulb and touch one point to the metal casing and the other one to my wire. It lights up but flickers.
    Shorting the neutral on the load side of the earth leakage to earth only usually causes tripping if there's current flow through the earth leakage.

    Some earth leakage units have internal electronics that draw a few microamps so it's possible when you disconnect the neutral on the load side it will appear to be at 230 volts on the empty neutral terminal to a digital tester that has an input impedance somewhere in the megaohm range. This would also probable be enough current to charge up the input capacitor on the CFL ballast to the point where it discharges intermittantly causing the tube to strike momentarily whils it drains....hence the flicker.

    The 10 volts on the supply side of the earth leakage is probably just the neutral-earth voltage of the installation.

    Quote Originally Posted by JustJohann View Post
    I then disconnect the neutral at the top of the earth leakage and connect a wire from the earth bar to the top of the earth leakage and do the same touching the cable from the bottom (which now should be a earth) to the one point of the lamp and the other point to the metal of the db which i did check was connected to the earth bar. It lit up ! What is going on here ? How can I get a voltage thats strong enough to light up a lamp between earth and earth by just passing it trough the earth leakage ? I reconnected everything as I found and told him to be very careful until I can have a decent look at just what is causing this strange fault.
    Again, the 10v neutral earth voltage might have been sufficient to charge up the input capacitor on the CFL ballast.

    The tests you're doing are highly unorthodox and the results are misleading. I'd advise against doing these kinds of tests because they'll run you around in circles chasing faults that don't exist. Bottom line is if the earth leakage has a supply connected to it and it doesn't trip when the test button is pressed then just replace it with a new one.
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    Quote Originally Posted by AndyD View Post
    Shorting the neutral on the load side of the earth leakage to earth only usually causes tripping if there's current flow through the earth leakage.
    Hell, am I glad there is at least one person who agrees with me. Said the same thing a couple of months back on this same forum and was basically told that I'm talking rubbish.

    Peace out .. Derek

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    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by Derlyn View Post
    Hell, am I glad there is at least one person who agrees with me. Said the same thing a couple of months back on this same forum and was basically told that I'm talking rubbish.
    And I had considered quoting your point on that one
    But thought I would leave it to you...

    Don't worry - I had taken notice when you raised the issue. Not all seed falls on stony ground.

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    Quote Originally Posted by AndyD View Post
    Shorting the neutral on the load side of the earth leakage to earth only usually causes tripping if there's current flow through the earth leakage.
    Excuse my ignorance ... when you touch a neutral wire and earth wire .... doesnt it generate a small current due to the circuit/wire resistance etc ?

    I have a nother one of these issues i am trying to understand ... I have a transformer which has only terminals 0 - 230 - 380 ... used for the control circuit in a machine and to run a cooling fan ... dont want to hijack this thread ... so i will start another thread ... someone mentioned an autotransfomer.
    Comments are based on opinion...not always facts....that's why people use an alias.

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    Diamond Member AndyD's Avatar
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    An earth leakage works very similar to using a clamp meter around the live and the neutral wires of a circuit simultaneously, what it sees is the difference in current flowing in the two wires. If there's no load on the circuits there would be zero Amps flowing in the live wire and (assuming an ideal world) if there's no voltage difference between the neutral and earth then shorting the neutral to earth won't result in any current flowing. So there's no current on the live, no current on the neutral, the difference in current between the live and neutral is zero as well hence the earth leakage shouldn't trip.
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    Diamond Member Justloadit's Avatar
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    Quote Originally Posted by AndyD View Post
    An earth leakage works very similar to using a clamp meter around the live and the neutral wires of a circuit simultaneously, what it sees is the difference in current flowing in the two wires. If there's no load on the circuits there would be zero Amps flowing in the live wire and (assuming an ideal world) if there's no voltage difference between the neutral and earth then shorting the neutral to earth won't result in any current flowing. So there's no current on the live, no current on the neutral, the difference in current between the live and neutral is zero as well hence the earth leakage shouldn't trip.
    True, however if there are some big loads running, then shorting the Neutral to Earth may cause another smaller current path to the Neutral of the transformer supply through Earth, unbalancing the L/N current that the Earth Leakage is sensing and may trip the ELU if greater than 20mA.
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    Quote Originally Posted by AndyD View Post
    An earth leakage works very similar to using a clamp meter around the live and the neutral wires of a circuit simultaneously, what it sees is the difference in current flowing in the two wires. If there's no load on the circuits there would be zero Amps flowing in the live wire and (assuming an ideal world) if there's no voltage difference between the neutral and earth then shorting the neutral to earth won't result in any current flowing. So there's no current on the live, no current on the neutral, the difference in current between the live and neutral is zero as well hence the earth leakage shouldn't trip.

    So i went into my workshop and found 4 earth leakage units CBI and clipsal connected 1 at a time.

    No wires out the bottom ... no load (current) ... no resistance ... "ideal world" ... imagine that every single earth leakage unit trips as i touch the neutral to earth.

    Derek or anyone else for that matter please prove me wrong by posting a video of you touching a neutral wire to earth that doesnt trip ... still waiting for the video promised months ago.

    We all understand the theory behind earth leakages and ohms law.
    Comments are based on opinion...not always facts....that's why people use an alias.

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    Quote Originally Posted by Dave A View Post
    And I had considered quoting your point on that one
    But thought I would leave it to you...

    Don't worry - I had taken notice when you raised the issue. Not all seed falls on stony ground.
    Have you got your "sparkies" to try it yet ... Hopefully you can post a video for us ? I will even drive to your workshop to see it in the flesh
    Comments are based on opinion...not always facts....that's why people use an alias.

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