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Thread: Fancy a guess at my next project?

  1. #41
    Join Date: Jan 2009

    Location: Essex

    Posts: 31,859
    I'm openingabottleofwine.

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    Quote Originally Posted by Blueflash View Post
    I take it that you are having the Primary 230v and the Secondary wired 115v - 0, 115 - 0 with the Red and Orange wires connected together and connected to earth which will give you balanced 230v.

    For safety you really need a double pole 30ma RCCB on the output otherwise if a fuse blows on the "Live" side you will still have 115v from "Neutral" to earth. I would recommend a Hagar 263U which is a 63A capacity but will trip both poles in a fault situation.
    Good advice - and supports my comments made on another BMU thread.

    However the current rating of the RCB fitted to the output should not exceed that of the transformer itself, so unless the transformer has a rating of 14.5kVA, the 63A rated breaker you mention is quite inappropriate, as it will only provide protection against differential currents but not for non-differential currents that exceed the current rating of the transformer.

    A 750VA transformer can only supply an in-phase current of 3A, so the double-pole RCB ought not have a current rating much greater than that.
    Barry

  2. #42
    Join Date: Mar 2014

    Location: Herefordshire

    Posts: 104
    I'm Alex.

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    Quote Originally Posted by Barry View Post
    Good advice - and supports my comments made on another BMU thread.

    However the current rating of the RCB fitted to the output should not exceed that of the transformer itself, so unless the transformer has a rating of 14.5kVA, the 63A rated breaker you mention is quite inappropriate, as it will only provide protection against differential currents but not for non-differential currents that exceed the current rating of the transformer.

    A 750VA transformer can only supply an in-phase current of 3A, so the double-pole RCB ought not have a current rating much greater than that.
    16A is the lowest that the RCCB`s go down to so whatever is fitted will not be suitable for short circuit protection unless you have over 3680 VA so choose the one with the better internal connections. I chose the 63A for it`s 10000A breaking current capacity for minimal contact resistance.

    For the short circuit protection you can then use a 2 pole MCB with the correct rating for the transformer, they go down to 2A.

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