Shower switch burnt and overloaded CU

[Luckyboy]

Called out today to odd smells and a very hot shower switch.

Investigated and found the Supply live conductor had burned/welded itself to the terminal on the switch. The screw wasn't as tight as I'd like it but also wasn't loose enough for any of the cables to fall out (except both CPCs).
Stripped back the cable and fitted a new 45A switch.
While I did this, I noticed that the load live cable had a tinned/silver look as opposed to the copper I would've expected. I stripped back a bit and it was still silver, is this due to the heat do you think? I can't strip back too much as they haven't left much slack.
It's a Triton shower, 9.5kW on a C40 RCBO fed with 10mm TW&E.


Looking at the Crabtree board, some MCBs have been swapped out for RCBOs. I have noticed that there is thermal damage to the Neutral bar - do you chaps think this could be due to overload? There are a number of heavy loads on this board;
1. Shower - 40A
2. Shower en suite - 40A
3. Oven - 40A
4. Kitchen ring - 32A
5. Socket ring (1) - 32A
6. Socket ring (2) - 32A
7. Towel rail - 16A
9. Fridge - 16A
10. Water Booster - 16A
11. Boiler - 16A
12. Lights - 6A
13. Lights - 6A
14. Lights - 6A
15. Smoke Alarm - 6A

Board is fed with 25mm SWA and is a top floor flat. What's your recommendation for next step? Obviously this board will need swapping but I don't want this to happen again in a few months time.

Thoughts would be appreciated.

 

[Murdoch]

I doubt that’s overload, more likely a loose connection on one of the neutrals.

 

[NozSpark]

Yeh, that Line conductor has thermal damage.... and the neutral bar and probably several of the terminated conductors

IMHO all the thermally damaged components need replacing, and the cables cut back to "bright copper".... otherwise it's just going to happen again and again

 

[SPECIAL LOCATION]

Back to basics IMHO...

Verify circuit wiring characteristics.. e.g. IR test values... R1+R2 values.. Ze, (Zdb)...

If they are all appropriate for the protective devices then should not be any problems if all terminations are mechanically sound.

Also any single gang, square accessory can be a bit of a sod to get decent mechanically sound terminations for 6.0mm / 10.0mm conductors..

Dead continuity tests should reveal a lot of clues..

 

[grumpyjohn01]

I dunno, could be overload at the board, 2 x 9.5kw showers & 40a cooker supply (just an oven or hob as well?) obvs that neutral link could have been loose, I have known those solid links to be tricky to maintain correct torque, doesn't explain the switch of course but as previously stated 10mm in a 1G pattern switch is very difficult to terminate adequately.