puffernutter
Puffernutter
- Messages
- 1,874
- Location
- Wiltshire
We had a bit of a smell in the hall on Saturday morning. Burning plastic. Tried a number of places - eventually traced it to one of my consumer units (installed by a Part P qualified electrician) a few years ago.
Here's what I found (same MCB, different views)
Here's the interesting bit! I did a little bit of forensic analysis and I think I know why - and it may be worth sharing.
This is the busbar side of the mcb. The preformed copper busbar has the first "tooth" intentionally bent to allow for the position of the main breaker terminal. However, this breaker is slightly (not by much, only 1mm or so) deeper than the rest of the mcbs and when I put the busbar in to the replacement mcb first, it was kept from making a really firm contact by this extra depth, In fact you could tighten it as much as you liked, but it would still pull out.
So if you did the breaker first, it would hold it tight and you could get a false impression of the security of the immediately next mcb, giving a slight resistance, giving heat etc.
The other mcbs will all tighten OK as they are that much further away and the angle means more of the copper is in the connection. This can re-inforce the false view as they will hold the busbar firm!
A salutory tale, lucky we were around to smell it!
Cheers
PN
Here's what I found (same MCB, different views)
Here's the interesting bit! I did a little bit of forensic analysis and I think I know why - and it may be worth sharing.
This is the busbar side of the mcb. The preformed copper busbar has the first "tooth" intentionally bent to allow for the position of the main breaker terminal. However, this breaker is slightly (not by much, only 1mm or so) deeper than the rest of the mcbs and when I put the busbar in to the replacement mcb first, it was kept from making a really firm contact by this extra depth, In fact you could tighten it as much as you liked, but it would still pull out.
So if you did the breaker first, it would hold it tight and you could get a false impression of the security of the immediately next mcb, giving a slight resistance, giving heat etc.
The other mcbs will all tighten OK as they are that much further away and the angle means more of the copper is in the connection. This can re-inforce the false view as they will hold the busbar firm!
A salutory tale, lucky we were around to smell it!
Cheers
PN