shower fuse


Postby bazza » Tue Feb 19, 2008 1:19 pm

hi everyone in my house i av a 8.5kw shower run on 6mm cable with a 30amp fuse but i calculate that the required size amps wud be 36.9amps (please correct me if im wrong) but if im right i was wondering if it wud be ok to replace the 30amp rewireable fuse with a 40 amp mcb ( wylex plug in replacements type b or a 32amp plug in replacement or are neither of these a suitable option and if not is it safe running of a 30amp rewireable fuse ? thanx 4 any replys cheers
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Postby ericmark » Tue Feb 19, 2008 9:28 pm

Yes you are correct 36.95 amps but if you look at Fig 3.2A at 10,000 seconds which is limit of chart it would take 45 amps to blow. i.e. 2.7 hours I don’t know how long you shower for? Looking at Fig 3.4 for type B 32A MCB or RCBO it has a similar time although curve is a different shape. In general fuses blow faster on short circuit and MCB trip faster on slight overload. It is of course the cable we are protecting and that will vary according to how it is run and 70°C or 90°C we normally consider 34 amp but it could drop to 23.5 or up to 62 amps. All for a 6mm² cable. But changing a 30 amp fuse for 32 amp MCB should cause no problems. But using a 40 amp MCB should anything go wrong with the shower (i.e. changed for a bigger one) then the cable could overheat and cause a fire before the trip opens. In real terms unlikely but why take the risk when there is no real need?
ericmark

Postby bazza » Wed Feb 20, 2008 7:41 pm

hi ericmark thanx 4 reply i will probably change it to a 32 amp mcb but just out of curiosity is it safe on a 30 amp rewireable fuse anyway ? thanx for replying cheers
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Postby bazza » Wed Feb 20, 2008 7:42 pm

hi ericmark thanx 4 reply i will probably change it to a 32 amp mcb but just out of curiosity is it safe on a 30 amp rewireable fuse anyway ? thanx for replying cheers
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Postby bazza » Wed Feb 20, 2008 7:43 pm

hi ericmark thanx 4 reply i will probably change it to a 32 amp mcb but just out of curiosity is it safe on a 30 amp rewireable fuse anyway ? thanx for replying cheers [color=blue][/color]
bazza
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