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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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  • Former Community Member
    0 Former Community Member
    John, we are definitely talking about the same parts, the bare NSX breaker is basically a preloaded spring based switch, so just needs a very light touch to trigger. The removable trip unit has some sort of piston that does this when required. I dont think the trip unit has any direct electrical connection as its display and LED's dont work until you get good few amps of load,e NSX I reckon (guess) when the switch part is closed the switch blades pass through holes in the trip unit which then gets its power via the transformer effect. The settings haven't been tampered with and the lowest ln setting on the 250A model is 100A, this trips out around 10-15 amps


    Alan, i'm not contemplating replacing the whole unit, its not a panel board, it's is a full size floor standing switchboard which would need quite a bit of dismantling to get to the input side of the device. My plan is to trip the device, remove the front cover, undo 3 torx screws and remove just the trip unit. My main concern is when the switch is open are the live parts really retracted into the shielded part of the case.
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  • Former Community Member
    0 Former Community Member
    John, we are definitely talking about the same parts, the bare NSX breaker is basically a preloaded spring based switch, so just needs a very light touch to trigger. The removable trip unit has some sort of piston that does this when required. I dont think the trip unit has any direct electrical connection as its display and LED's dont work until you get good few amps of load,e NSX I reckon (guess) when the switch part is closed the switch blades pass through holes in the trip unit which then gets its power via the transformer effect. The settings haven't been tampered with and the lowest ln setting on the 250A model is 100A, this trips out around 10-15 amps


    Alan, i'm not contemplating replacing the whole unit, its not a panel board, it's is a full size floor standing switchboard which would need quite a bit of dismantling to get to the input side of the device. My plan is to trip the device, remove the front cover, undo 3 torx screws and remove just the trip unit. My main concern is when the switch is open are the live parts really retracted into the shielded part of the case.
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