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10 November 2014 02:57 PM
Bhilly Posts: 51 Joined: 17 June 2013	LFB originally stated that the change to metal CU's would prevent fires; thankfully, BEAMA have corrected this by saying that the intention is to contain the fire for longer. Is this a good thing? Not necessarily, if you want to give the occupant as much warning as possible. Also, the increased containment relies upon the installation being sealed correctly - no point having a nice metal box if there's a great big hole in the wall it's sitting on.
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10 November 2014 03:13 PM
davezawadi Posts: 4259 Joined: 26 June 2002	I'm not sure that it can be creep OMS, whilst copper can get some plastic deformation at high loads and low temperatures, it is likely that you would need about 350 - 400 degrees C to initiate real creep, and that is not the normal working temperature. As the problem is new, it cannot be that anyway, in fact I don't think it is loose terminals at all (unless smart meter installations have something to do with it), I am more suspicious of the steel terminal bars which are pretty thin around the clamp screw holes. I'm just going to try to set a MCB on fire with a real arc (from welder), report later! ------------------------- David BSc CEng MIET
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10 November 2014 03:23 PM
jcm256 Posts: 2327 Joined: 01 April 2006	According to this article there are a lot of things that brought this problem into being, electricians, manufactures, inferior plastics, bad workman ship, and single screws in terminals, overlooking the importance of the neutral.. It is obvious that this long interesting thread has not reached a natural finish yet. http://www.eponthenet.net/arti...r-consumer-units.aspx jcm
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10 November 2014 03:39 PM
Zoomup Posts: 6117 Joined: 20 February 2014	Originally posted by: jcm256 According to this article there are a lot of things that brought this problem into being, electricians, manufactures, inferior plastics, bad workman ship, and single screws in terminals, overlooking the importance of the neutral.. It is obvious that this long interesting thread has not reached a natural finish yet. http://www.eponthenet.net/arti...umer-units.aspx jcm Hello jcm. the report in your link is very interesting. In the second picture, that is the close up of the cut out and burnt consumer unit, I get the impression that the tails connect directly from the cut out to the consumer unit. I can not see a meter. Am I correct? Perhaps your eyes are sharper than mine? Bye, Z.
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10 November 2014 04:50 PM
mapj1 Posts: 12039 Joined: 22 July 2004	Its red link - its not company fuse in there either. I'd imagine that metering for a group of flats and a real cut out are in the basement somewhere, or maybe even outside in a plastic box, and there is a 'building network' between metering and a second tier of cut-outs. (There is also sometimes such a thing as a "building network operator", which is whichever poor sap is now responsible for cables, splitters and cut-outs probably put in by the electricity board half a century ago, but now disowned by both metering company and DNO. In some cases this can include wiring between the cut-out and the meters, which in addition introduces a responsibility to protect against abstractions. ) ------------------------- regards Mike
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10 November 2014 07:18 PM
davezawadi Posts: 4259 Joined: 26 June 2002	Interesting OMS but I seem to remember (from a certain Dr Wright, who was very difficult to understand at all!) there is a cubic time term in creep equations, which means that loose in 1000 hours at 300C (say 600k) would be loose in 1000,000 at 300k, and so significant heat would have to be there. Regards David ------------------------- David BSc CEng MIET
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10 November 2014 07:23 PM
davezawadi Posts: 4259 Joined: 26 June 2002	I hate that term, so inaccurate, electrical resistance heating. Of course there is heating in resistances, in many ways bad connection is a much better description. I got interrupted in the fire test, will resume tomorrow. Regards ------------------------- David BSc CEng MIET
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10 November 2014 03:23 PM
OMS Posts: 22864 Joined: 23 March 2004	Maybe Dave - I was working to about 1% creep per 1000 hours at 150C and then extrapolating back to how many thousand hours at say 50C - it's several tens of 1000's of hours to be sure - but consumer units are in place for a lot of years I guess Play safe if you are doing real fires Regards OMS ------------------------- Let the wind blow you, across a big floor.
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