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Thread: Fault finding

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    Fault finding

    Greetings

    I have a customer that called as his main breaker (3 phase 45 amp) trips intermittently.

    So I went out balanced the phases and grade the circuit breakers correctly (breaker from main DB feeding sub DB was the same size as the main breaker)

    Ciruits seem clear when tested.

    I left and the same fault persists, advice please?

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    try a D cure or curve 1 breaker...if that doesnt work then install a PQA and see what time it trips and why it is tripping...overload or fault.

    if you dont have a PQA...then its just a guessing game.

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    Thank you

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    Diamond Member AndyD's Avatar
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    Is it normal domestic circuits like stove, geyser, plugs and lights?
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    Hi Andy

    The circuits are ups, plugs, lights and aircons. It is a shop at the Waterfront.

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    Diamond Member AndyD's Avatar
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    Eek, 45A per phase isn't much if it's a commercial premises with geyser, air con, probably lots of LED lights with horiffic inrush currents and power factor and gawd knows what else they're plugging in.

    If you don't have access to a PQA or data logger you can prove whether it's a fault or a general overload condition by installing a second temporary 'main breaker' downstream from the existing one and make it a higher current rating. In this case I'd probably go with a 60A breaker but obviously whether this is a viable option or not depends on whether there's space in the DB. If the 60 Amp breaker stays up next time the power trips then it's an overload problem, if it trips simultaneously along with the 45A main breaker then there's a very good chance it's an intermittant fault either somewhere on the installation or on one of the items plugged in.
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    SeanM (04-Jan-19)

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    Morning Andy

    This is really good advise, I would never of thought of putting a secondary breaker in.

    An update I changed the main breaker to a 50 amp 3 phase (the main cable is a 10mm) , I am not a fan of just increasing breaker sizes.

    And to date no tripping

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