Schneider NSX micrologic trip units

John Peckham:

Geez


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

Interesting comments below this clip as well.

How to repair Schneider Electric circuit breaker simply and fast - YouTube


Z.

John Peckham:

Geez


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

The cautionary notice, which whizzes by at the beginning says work dead. It's all very well demonstrating the process on a work bench where uninsulated tools present no hazard, but the lower terminals seem to be exposed during this process. If they are on the load side, that may be an acceptable risk.


Switching off a whole block of flats for a few minutes may be a nuisance, but bear in mind R.14 of EAWR 1989!

Geez:

Chris


Its not just a block of flats, its a large building network and these devices are way before any metering. Basically DNO transformer to my 1600A ACB in switchboard, switchboard busbars to 9x MCCB's (mixture of 400's and 250's) these feed the Ryefields to 7 blocks of flats and 2 retail units. The Ryefields in each block feed the communals of the block and EVERY flat. So my faulty 250 is directly connected to the ACB and feeds one block of flats (communal and flats). The only way I can isolate the 250 is by opening the 1600. If I can safely swap out trip unit it avoids isolating the other 6 blocks and 2 retail units.


John


I watched all those vids and spoke to Schneider before posting this but I missed the comments you mentioned, real pity the Schneider guy didn't answer the one about the 40A device tripping on low load when set to 28A, similar to my fault but mine is set to full (250A)

So, a chain is only as strong as its weakest link. It appears to be a poorly designed installation.


Z.

Geez:

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

Does page 13 help at all?

Compact NSX Micrologic 5/6/7 - Electronic Trip Units - User Guide - 01/2020 (schneider-electric.com)


P.S. Internal Power Supply for Micrologic 5 and 6 Trip Units The protection functions and the test functions of Micrologic 5 and 6 trip units operate with the current through the internal current transformers (CT). When the load current is higher than 20% of the rated current In, the internal current supply provides the power supply for the full functioning of the Micrologic trip unit. This includes:  The Micrologic display screen and LEDs  The maintenance and diagnostic functions To provide a power supply to the Micrologic 5 or 6 trip unit when the load is below 20% of the rated current In, and maintain the full functioning of the Micrologic trip unit, one of the following optional power supplies can be used:  An external 24 Vdc power supply connected permanently to the Micrologic trip unit  A power supply connected temporarily to the test port on the Micrologic trip unit:  Pocket battery  PC through USB maintenance interface Each optional Micrologic power supply is described further.


P.P.S.

HAZARD OF ELECTRIC SHOCK, EXPLOSION, OR ARC FLASH  If the trip unit displays a St0p screen, replace the Micrologic trip unit immediately.  If trip unit displays a fault screen, do not close the circuit breaker again without first inspecting and, if necessary, repairing the downstream electrical equipment.  Apply appropriate personal protective equipment (PPE) and follow safe electrical work practices. See NFPA 70E or CSA Z462 or local equivalent.  This equipment must only be installed and serviced by qualified electrical personnel.  Turn off all power supplying this equipment before working on or inside equipment.  Always use a properly rated voltage sensing device to confirm that power is off.  Replace all devices, doors, and covers before turning on power to this equipment. Failure to follow these instructions will result in death or serious injury

Z.

Geez:

Chris


Its not just a block of flats ...

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. 

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. 

 

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.