MCB FAULTY? Help!
- Thread starter JayDiy
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Right guys I have finally got to the bottom of this, there are no loose connections anywhere, so I opened up the cooker connector box and behind it I could see that the wire seemed to be coming through the plaster horizontally and going toward the adjacent unit where I have another microwave/2nd oven, so I removed this appliance and to my surprise I found a fused spur switch with 13amp fusewhich had blown, which now explains why the 40amp mcb didn’t trip, I am very annoyed that the electricians would do such a thing. So anyway it’s now sorted. Thanks guys for all your help. Cheers!
I'm glad that you found the FCU and have, at least temporarily, solved your problem!
However, do you know why the fuse blew. There's usually a reason, which means that (since you presumably have done nothing to remove any reason) there is a good chance that the new fuse may also blow in due course.
Kind Regards, John
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Was that the first time you had ever used the cooker?
Are you sure the cooker supply is actually routed throught the 13A fuse?
Are you sure the cooker supply is actually routed throught the 13A fuse?
As EFLI has implied, if a load which drew 40A was connected via a 13A fuse, it would never have worked (fuse would have blown first time it was switched on) - was that the case?
The instructions for the cooker may say (almost certainly unnecessarily) that it should be connected to a "40 A supply", but it is very unlikely that it would actually require a supply anything like that large.
Do I take it that the 'cooker' really is a 'full cooker' (i.e. an oven plus hob)? Ovens alone are often designed to run of a 13A supply (e.g. through a plug/socket) and, even those which need a bit more than that probably don't usually draw enough current to blow a 13A fuse.
Kind Regards, John
No, I’ve been using cooker for a few months now without any problems, and yes was actually routed through the 13amp fused socket because I tested it and also confirmed it was the fatter cooker cable coming into it. I’m ****ed off with those electricians who did this in first place.
Fair enough. By application of the accepted principle of diversity, A 5kW oven, in itself, would be deemed to take ('an average of') about 13.5A, which would never blow a 13A fuse. However, if this was perhaps the first/only time you had also run the two appliances simultaneously (through the same 13A fuse) that might well be the reason why the fuse blew on this occasion.
It takes something like 22A to blow a 13A fuse in an FCU (which means that a sustained 5kW load {which an oven would never actually present} would quite probably not blow it), and that corresponds (with application of 'diversity') to a peak (i.e. the total stated 'ratings' of the appliances) total load of around 11.5 kW
Kind Regards, John
Are you sure it wasn't a kitchen fitter?
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What is the maximum load of the oven?
Is that not what the "5kW" the OP told us will be?
If so, as I said, that corresponds to around 13.5A after diversity (a bit less if, as is likely, the "5kW" relates to 240V). Even without diversity, it would be a fraction under 22A, so a 13A BS1362 would be unlikley to blow even if it were drawing 5kW continuously (which obviously wouldn't happen). However, with a microwave load on top of that, it might well blow the fuse.
Kind Regards, John
You may be right they were general builders doing everything under supervision of the contractor.
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