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commercial kitchen DB

Efabian

I had a call out to look at a hotel kitchens extract fan that had had the supply cable live connection melt, either a loose cable connection or loose grip on the fusecarrier within the transformer type speed controller. No real damage apart from a bit of melted insulation and black copper, was a 4mm on a C20 MCB. 

The fan was rated at 8.78 A so I installed a 13A FCU before the speed controller and cleaned up the cables, tested and reconnected.  Zs tested out ok for the mcb. Question is when I looked at the mcb it and some of the others were covered in crap, most likely grease as the db is at high level at the end of the canopy covering the cooking line. The DB had a recent EICR sticker, (May 22) but I've not seen the report or know what, if any recommendations were made. 

I suggested that the mcbs were changed for new, crabtree 3 phase db so still widely available, but apart from zs and functional switching on the dolly any other way of checking the mcbs are still within spec. I'm a bit concerned about the ambient temp when the kitchen is in full swing but because the extract fan had failed no cooking was going on when I was there. 

Relatively clean inside DB but very grubby on the front, not the best fitting cover either.

Would a AFDD have fired off due to the arcing on the connection, staff were saying that they had been unable to run the fan higher than 3, out of 5 speeds because it would stop working but obviously carried on until it broke completely. 

  • Hmm, I've seen far worse than that in kitchens. An engineering factory was the worst I'd seen, lots of black dust inside the DB.

    It is clearly not great, but I don't think I'd be changing the CBs, the 20 amp CB would never trip on a 9A load, even with a bit of sparking going on. You've negated matters somewhat by fitting the 13A fuse, but would that fuse go before the 20A CB?  I'd doubt it, a 10A CB may be a better choice.

    As for AFDDs, I have read somehwere that they are not good on low loads, so may not have tripped either? Somewhat more clued up on their benefits and disadvantages needs to comment on that.

  • I suppose that if it really mattered, the DB could be cleaned.

    Now then, more importantly, are any of those MCBs being used for functional switching?

  • If that is the worst of it, it has some way to go to win any prizes for worst DB. Clearly not the best location but if the insides look clean I'd not worry too much. If there is  evidence of condensing moisture and rust would worry me more.. It may benefit from a wipe down with the power off, but that would be largely cosmetic .

    In your shoes I'd not be too worried.  It is hard to say if an AFDD would have tripped, and even if it had,  would they have just have reset it 'the show must go on' ?  Without a what to do if the trip fires procedure, that is the most common action.

    If you really want to check MCBs without a proper testbed, the fastest way is with a car battery, being about the only portable thing capable of generating the large currents needed, but I'd really not bother, mcbs are not delicate things like RCDs with almost no actuation energy,  if the fault current it high enough, they will let go.

    Mike.

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