Another variable to chuck into the arena is this - some folk religiously switch on and off their shower isolators after each use whilst others are content to just leave the switch in the ON position until something fails, yet we still see problems regardless of frequency of use or lack of.

The one I did recently cannot have been touched in the 9 months since it was installed - it being sited behind a heavy double wardrobe, yet it still burnt out. Same with cooker switches unless they incorporate a socket and are situated on the wall above worktop height - most people seem to leave them permanently ON, and those buried inside kitchen units never get touched at all.

I would suspect that the dissimilar metals thing is indeed a contributory factor, especially when we move further away from copper to steel. All-brass construction didn't seem to be as big or common a problem back in the day. If it burned, then usually it could be put down to a loose connection. What I have found is that the steel screws are still tight when it comes to changing out the faulty item - not burnt/welded tight due to molten material clogging up the threads, but mechanically tight. So suggestion is that the cause was a high resistance connection inside the unit itself.

It is a fair point that some of these switches are not used but still exhibit the same issue, my comments were based on how I use my shower.

It has always amazed me the amount of effort put into choosing cable when it comes to loading and heat rejection in comparison to the actual contact area within switches. Perhaps the heat is generated there and conducts to the cable terminal. Not sure why this would only affect the neutral though. Does anyone fancy changing their house to 230V two phase power to see what happens to their shower switch?

I remember reading in another forum some time ago about this neutral problem. Someone suggested that the N and L terminals were treated differently by the installer, L being more "important" therefore needing an extra tweak with the screwdriver. Which is perhaps what Chris was saying when he mentioned confirmation bias.

I had an interesting one today.

Tenant is a vulnerable person who is not showering daily. Tenant seems to be confused between the bathroom light pull-cord and the shower one, so sometimes the shower does not work and the tenant remains unwashed.

There we have it, another reason for not having an isolator in the room.

Item number 4 given a code 2 by this inspector! Joe Public is certainly at the mercy of the of the highly subjective nature of condition reporting and sometimes the ignorance of the so-called inspector!

Seems a bit random. Did the absent blanks get a C1?

Oh dear. I thought the message that EICRs should describe the problems, rather that dictate particular solutions, had got out there.... apparently not.

   - Andy.

Tricky, perhaps coloured strings or just cut it to be  very short cord that con only be reached with a chair. These are the sort of things that make you realise one size does not fit all cases.
It also sounds like the sort of case where a consumer unit at easy access level and manual reset RCDs may  not be the good idea it a first appears.
Mike.

The difference in the current standard makes very little difference between a 40-50A switches and making it =>50A reduces the operations by half when tested.
Heat rise at the terminal is a max of 45K. I think the un-operating test is 125C (don't you love BSI for mixing units in one document).
I uprated all my isolators to 50A and they passes. I also upgraded my double pole to 32A by just increasing the hole size in the terminals.