Niglon RCBO stuck in MK LN board

[Tontoe]

I had a call to a new customer who was experiencing what sounded like nuisance tripping on a kitchen ring.

Some background first.

1. It's an MK LN insulated [i.e. plastic] split load board, with only one side RCD protected. A direct predecessor [I think ?] and very similar in appearance to the plastic MK Sentry boards we know and love :-(
2. At some stage, the customer has had an extension built, and the existing split-load board seems to have had the original MCBs on the unprotected side replaced with individual NIGLON RCBOs [presumably because they were cheaper at the time than the MK Sentry RCBOs which I think would have fitted]. The other side, with a mix of MK & NIGLON MCBs is protected by the OEM 80A RCCB.
3. The 32A RCBO concerned was off, and popped off on trying to reset it. The customer said it would "used to stay on, but nowadays trips more or less constantly"

So:

I made sure all loads were disconnected. The RCBO still tripped, so not an appliance.

I disconnected conductors at the RCBO and tested the circuit:

1. Ring conductors all continuous with similar readings [and expected values] for R1 & Rn, and the expected reading for R2.
2. Insulation tests [@500V with all loads disconnected] ]showed >999 Megohms on P-N, P-E & N-E.

Figured it was the RCBO then. I reset it, and on the third attempt it stayed set. I then tested it with no loads connected. It tripped at 50% and wouldn't go any further.
I thought I'd just remove it and replace with an MK model. I'm fairly sure Sentry RCBOs fit these old LN type busbars with the right-angled fingers - seem to remember fitting a couple a few years back.

But I might be wrong?

Anyway... I released the busbar [after isolating the supply of course

] and the DIN rail locking catch on the RCBO. However, the RCBO stayed firmly where it was. I couldn't get it off the DIN rail.

I then had a closer look underneath, and it looks as if the original busbar is cut short, and extended with [perhaps?] a piece cannibalised from another type.

I think I have a complete old-type LN busbar somewhere, but what is worrying me is not being able easily to remove the RCBO.

I don't want to force it, break something and then have to do a board change for free. I wonder whether the person doing the mods possibly found the Niglon RCBOs "almost" fitted, but needed some persuasion and are now somehow jammed on the DIN rail?

[BTW don't get me started on the number of 32A circuits on a 60A Main Fuse -

]

Have I missed something blindingly obvious? I await scorn, brickbats etc...

 

[buzzlightyear]

Those rcbo should have not been fitted in the beginning, new board me thinks.

 

[littlespark]

Disconnect a few things, remove all the breakers to the left of the stuck one, and see if it will slide off the rail.

It’s maybe just a very tight fit with it not being designed to match an MK rail.

 

[Rockingit]

Remove the adjacent devices, slacken off ALL the bus terminals...... carefully placed whack with hammer.

After you've got it out, proceed to remove the rest of it and replace with a new board.

 

[Tontoe]

Those rcbo should have not been fitted in the beginning, new board me thinks.

My thoughts exactly! Snowed under with work at the moment, so might have to pass it on