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Schneider NSX micrologic trip units

Former Community Member
Former Community Member
Had a callout to a block of flats last night where one of these devices (250A) had tripped. Cause seems to be a fault on a lift, as its own 100A downstream device also tripped, so obviously not set correctly for discrimination. Problem is that after restoring the 250A device it now trips on a very small load, literally a couple of amps per phase. Wondered if anyone has seen this before? has the trip unit been destroyed by the fault or has its electronics got into a pickle?


As it was night time there was not enough load to even light the micrologic display. As a temp clear I managed to move the circuit onto an unused 100A device in the panel but for 13 flats and the communals dont know how long ill get away with that.


PS can the trip units be replaced safely on these units without isolating the upstream device, this would be a 1600A ACB feeding a very large development.


Thanks in advance


Tom
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  • 0
    Geez:
    Chris Pearson:
    Geez:

    Chris


    Its not just a block of flats ...

    Tom, whilst my experience is at the domestic end of the scale, the law is the same. EAWR 1989:

    Work on or near live conductors



    14.  No person shall be engaged in any work activity on or so near any live conductor (other than one suitably covered with insulating material so as to prevent danger) that danger may arise unless–



    (a)it is unreasonable in all the circumstances for it to be dead; and



    (b)it is reasonable in all the circumstances for him to be at work on or near it while it is live; and



    (c)suitable precautions (including where necessary the provision of suitable protective equipment) are taken to prevent injury.


    Back to your OP, I am not sure that anybody here would wish to give you a firm assurance that replacing the trip device whilst the switch is live is entirely safe. Only you can decide what is reasonable or unreasonable here. 

     



    Agreed, but if you were working on a domestic consumer unit with the main switch off you still have live terminals at the top of the main switch. An NSX breaker is basically a switch disconnector with a trip unit attached to the bottom. What I'm  trying to establish is when the switch disconnector part is in the off position is bottom of the unit just the same as your dead busbar in a domestic CU.


    I wonder if you could switch off at 2 a.m. when most people are asleep and the shops will be closed? Perhaps you could post notices around and about warning of the impending switch off in advance. Then the work would be less disruptive. It is best to work with the supply disconnected.


    Z.


Reply
  • 0
    Geez:
    Chris Pearson:
    Geez:

    Chris


    Its not just a block of flats ...

    Tom, whilst my experience is at the domestic end of the scale, the law is the same. EAWR 1989:

    Work on or near live conductors



    14.  No person shall be engaged in any work activity on or so near any live conductor (other than one suitably covered with insulating material so as to prevent danger) that danger may arise unless–



    (a)it is unreasonable in all the circumstances for it to be dead; and



    (b)it is reasonable in all the circumstances for him to be at work on or near it while it is live; and



    (c)suitable precautions (including where necessary the provision of suitable protective equipment) are taken to prevent injury.


    Back to your OP, I am not sure that anybody here would wish to give you a firm assurance that replacing the trip device whilst the switch is live is entirely safe. Only you can decide what is reasonable or unreasonable here. 

     



    Agreed, but if you were working on a domestic consumer unit with the main switch off you still have live terminals at the top of the main switch. An NSX breaker is basically a switch disconnector with a trip unit attached to the bottom. What I'm  trying to establish is when the switch disconnector part is in the off position is bottom of the unit just the same as your dead busbar in a domestic CU.


    I wonder if you could switch off at 2 a.m. when most people are asleep and the shops will be closed? Perhaps you could post notices around and about warning of the impending switch off in advance. Then the work would be less disruptive. It is best to work with the supply disconnected.


    Z.


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