Replacing MCB

[Grumps]

Typically, or more specifically an MK Sentry CU, can you replace an MCB without dropping the busbar from all the other MCBs?

[Chris Green]

Supposedly yes, but often no, is my experience. You just have to try it. There's sometimes a spring latch on the MCB that clips it to the DIN bracket along the back, often difficult to find and reach to unlatch.

[ARW]

The MK ones are usually OK if it is a plastic CU.

Drop the clip with a flat headed VDE screwdriver and then FULLY undo the bus bar terminal screw. Gently prise the bottom of the MCB forwards a few mm and then lift straight up.

Reversal is the opposite.

[ARW]

Or nearly the same....[1]

On reversal drop the clip before putting it back on the MCB and push the clip up once it is on the bus bar.

Also MK MCBs are of the sort you cannot get the busbar trapped behind the MCB terminal.

[1] If I had finished of my reply with "then push the clip back up" it would be a reversal".

[John Rumm]

I have done it on several CUs - and I think at least some were MK ones.

Undo the bottom screw completely, then get a small screwdriver into the tag on the spring clip and release it while pulling the MCB toward you. That should allow enough wiggle room to unhook the bottom off the DIN rail. Then it will lift straight up.

[Grumps]

Thanks guys. I'll give it a shot tomorrow (if the sun shines).

[ARW]

I took it that Grumps was doing this live.

If the power is off it is far easier just to remove the bus bar.

[Grumps]

I don't think I'll attempt it live. Would a professional do it live?

[Smolley]

Not without an approved written risk assessment detailing the procedure and why it has to be done live.

[ARW]

Yes if needs must.

[ARW]

Are we in a house or a hospital?