MCB reset tab + switch?

[Trogdor]

Hi
Last night my lighting MCB tripped out when a bulb blew, after flicking the switch back into place the power was not restored to the lights.

This morning I opened up the panel to see what could be wrong, I stumbled upon a 'tab' at the base of the MCB which i pulled down with a screw driver, this didnt reveal much so i pushed it back into place, I then tested the MCB and found it to be conducting again?

Could someone tell me what this tab actually does, and why the MCB was off even when it was in the on position? I have no manuals etc supplied with my electrics so I'm in the dark on this (if you'll excuse the pun).

Cheers,
Nik

 

[brown-nought]

SAFTY FIRST: Please tell us you switch off the whole CU before stumbling around. Touch the live bus bar and you will end up at best badly burnt, worst dead

The "tab" was most likely the DIN rail connector. It has no effect on the MCB’s operation – its there to hold the MCB against the mounting rails.

Most MCB’s operate independently of the toggle switch. This allows them to still trip when held in an on position. It sounds like your MCB may be dodgy, sticking or immediately tripping. I’d consider getting it replaced if it happens again.

 

[Trogdor]

Hi

Thanks very much for your reply!

Yep, i did indeed turn the the CU off before messing around in there!! Im not finished up in this world quite yet!

I shall be replacing the MCB next time it sticks, or i find myself near a supplier.

Cheers,
Nik.

 

[Lectrician]

Possibly the terminal is resting on the busbar, but not tightened onto it, or the clamp of the terminal is on the wrong side of the busbar.

Seen this countless times!

 

[ban-all-sheds]

Yep, i did indeed turn the the CU off before messing around in there!! Im not finished up in this world quite yet!

Turn it off again and check that the terminal screws for the busbar and outgoing cable are tight. A loose mounting o the rail won't cause electrical problems, but a loose electrical connection can be dangerous.