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Earth Leakage Trip explosive gas environment

Stephen Biddle
Hi All


I have a question relating to the Earth Leakage Trip level for an electric heater, heating natural gas for a generator.  As I remember to level specified in IEC 60079 is 100 mA.  My problem is I have a long run of cable to the heater from a thyristor controller and I have to set the trip to 500 mA to avoid spurious trips due to cable capaciatance to ground.  Does this then not comply with the EIC spec?  My justification is that 400 mA of the earth current are running through the capacitor, so leaving 100 mA for a genuine insulation failure.


Thanks


Stephen
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    I think you will find there are capacitors inside the thyristor unit,  as in deliberate components with two legs each, probably in a desperate bid to meet EMC requirements.Which side of the controller is the RCD ?

    However, even so, 500j ohms of imbalance is a lot - 1uF is ~ 3K ohms a 50Hz and to suggest you have 6 uF more on one phase than the other two is not the sort of thing to be found in sub kilometer cable capacitnace. As a capacitor at mains voltage look for something the size of a small salt celler. example
    https://www.lampshoponline.com/6uf-capacitor.html


    Realise that if the capacitance to ground from all 3 phases is equal, the net leakage is zero, much like balanced resistive loads have no neutral current.

    So I'd be looking if something that should have been be 'neutralled' has been 'earthed' as a wire saving measure, perhaps an auxiliary supply for display or a cooling fan or  a similar c*** up.


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  • 0
    I think you will find there are capacitors inside the thyristor unit,  as in deliberate components with two legs each, probably in a desperate bid to meet EMC requirements.Which side of the controller is the RCD ?

    However, even so, 500j ohms of imbalance is a lot - 1uF is ~ 3K ohms a 50Hz and to suggest you have 6 uF more on one phase than the other two is not the sort of thing to be found in sub kilometer cable capacitnace. As a capacitor at mains voltage look for something the size of a small salt celler. example
    https://www.lampshoponline.com/6uf-capacitor.html


    Realise that if the capacitance to ground from all 3 phases is equal, the net leakage is zero, much like balanced resistive loads have no neutral current.

    So I'd be looking if something that should have been be 'neutralled' has been 'earthed' as a wire saving measure, perhaps an auxiliary supply for display or a cooling fan or  a similar c*** up.


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