Schneider NSX micrologic trip units

Does it have an earth fault trip module  enabled ? - if so and there is an N-E fault in the lift or else where, it may be seeing your 1-2A load as an earth fault and flipping on that, much like an RCD will often trip on a part loaded circuit with an NE fault of modest resistance (as the current splits and some that should have come back via the neutral escapes to earth, and the trip sees the L-N imbalance when the percentage of the load escaping meets the trip setting)

If you have photos, or the part numbers it may be possible to say more.

It may also be worth talking to the

It is a 5.2E unit so no earth fault protection and the faulty lift is still isolated. I can reset the device with no load, then as I start turning on the isolators to the 13 flats it trips after I get 5 or 6 on, any 5 or 6 so not a fault in one of them just when there's enough load, which was less than 20A across all the phases according to my clamp meter.

Am I right in thinking   one of these  ?

I'm not at all familiar with the details of this one, but the 'end of life' instruction (pic below) suggests the sensor and PCB  unbolts.from the breaker mechanical part, but it is not clear to me if that can be done 'in place' or if more has to be dismantled.

In your situation I'd call them and your favourite supplier, and ask 2 things,

1)can it be swapped in place and

2) how much does one cost on sale or return...

Yes, the trip units are separate and removable and can be done in situ but Schneider were not very helpful about whether that can be done with the incoming terminals live but unit tripped, they just quote that is live working and we don't recommend it.It does look like the live parts are well away from from the trip unit when the switch is off. I will need to get that clarified though as the only thing between me and the DNO transformer is about 15ft of cable and a 1600A air circuit breaker.

Hmm. in your shoes at least verify on, then lock it off,  and then verify it really really has gone off and that no amount of knocking or shaking or waggling the actuator  can posibly turn it back on. The sensors must (should) be on the dead (output) side if it is wired properly.

May be need to arrange the input terminals covered with something to prevent anything falling into the works if there are long supply side lugs visible that are always live also.

Not sure if there is a fancy torque setting bolt  - the drawings look like the screws on a new one are longer than when fitted - does a big head shear off at the right setting, to reveal a smaller head only for removal ? Seems overkill if so , but in some way typically Germanic.

May be better to wait for someone who has used one to respond, I haven't.



M.

My chain of thought exactly. Would be really helpful if someone who's had one apart chips in. Would also be handy to have a complete unit to take apart and see exactly how shrouded (or not) the incoming terminals are.

I have seen it done but not sure if it can be done on all models of micro logics and NSX breakers. Give Schneider technical a call they are very helpful.


Some of the units have a red LED that lights when close to operation. Has anyone tampered with the micro logic settings?

I've replaced one of these breakers with the board live still. This was on a new board around 4 years ago, so older ones may be different.

IIRC, there wasnt anything that worried me about replacing it. I think the busbar bolts are plastic, or I may be thinking of another board, but if it is these, it is a 17mm socket head bolt, I havent got an insulated socket wrench, so probably was plastic.

None of the other live parts are accessible without a thin screwdriver, you cannot inadvertently put a finger on a live terminal on the modern Schneider large panels.

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.

Geez


Have a look at this https://www.youtube.com/watch?v=_VWaytGcAxU