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3 Phase split in to singles then back?

Discussion in 'Electrics UK' started by Hager, 5 Oct 2011.

  1. Hager

    Hager

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    Hi

    I've recently found out that in one of our DB's we have 3x 63A Single phase breakers supplying a 2nd DB which is a 3 phase unit. each breaker supplys Brown, Black and Grey phase to the 2nd DB.

    Am i right in thinking this need to be replaced with a single 63A 3 phase breaker??
     
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  3. ricicle

    ricicle

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    Yes. You are correct.
     
  4. ericmark

    ericmark

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    537.1.4 is the regulation. But although it refers to linked it is only for the isolation function and as far as I can see the only place where MCB's must be linked is 554.1 Electrode water heaters and boilers.

    554.3.4 is only place where a fuse is not permitted.

    There is a reference when using autotransformer 555.1.3 but as with 537.1.4 only where the braker is a switch/isolator as well as overload.

    So unless the installation includes electrode water heaters and boilers then there is nothing to force you to use a linked MCB. You could use fuses if you wished which are of course not linked.

    However good practice where non linked protection is used would be to include anti-single phase devices with every three phase motor and in real terms if any motors are used then one would normally use linked MCB's. But there is nothing to say you must.
     
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