HELP!! Blown Fuse board

tom-the-sparky · Nov 4, 2010

Hi everyone, before u ask qualified electrician speaking here. The shower blew last night, but i cannot figure out why ive got a 6mm cable through crimped at the board protected by a 40a breaker, but the cable seriously overheated causing an earth fault and a massive bang!! I'm sure 40a ok for 6mm, could it be the through crimp??? Help!!!!

Spudnik · Nov 4, 2010

Could be the crimp, but i would hazard a guess that the cable should have been protected with a 32A mcb.

AlanWirral · Nov 4, 2010

Is it RCD protected??? Also why the through crimps??

Sintra · Nov 4, 2010

The only acceptable installation method for a 6mm cable on a 40A is clipped direct.

bugsy · Nov 4, 2010

Through crimps could cause overheating if they were loose but not a short ( which you seem to discribe ) nor would overloading the cable by a few amps. have you tested the cable / shower

SirKit Breaker · Nov 4, 2010

At what point on the cable did it overheat and short out? was it at the crimp? What is the rating of the shower? I have seen loads of tripped showers where the neutral has burnt out in the pull switch due to bad connections, so your crimp could be the culprit if it wasn't tight. But it is one of those which would need to be seen to give an accurate answer. 40a on a 6mm cable is Ok depending on the installation method, but 32a would be better.

tom-the-sparky · Nov 4, 2010

thanks for replys chaps. i'm thinking it must be to do with the through crimp (due to short cables needing extending), this is where most of the damage looks to have taken place! Also i hear what your saying about it being on a 32a mcb but was previously on a 40a with no problems!! But may change it to a 32a anyway, after tests on the cable to check its integrity!!

AlanWirral · Nov 4, 2010

Loose connection in the crimp then hey. What rating is the shower then?

tom-the-sparky · Nov 4, 2010

9.5kw shower i think, if i could rip out and start again 10mm for a shower every time!

rocker · Nov 5, 2010

Yea that's too big for 6mm unless it's reference method C - check your BRB.

9.5kW pulls over 41 amps at 230 so even increasing the breaker to 40a, which again shouldnt be done unless the cable is installed to ref meth C, isn't necessarily going to take the full power of the shower.

You say in another post you have NIC coming - you need to increase the size of the cable or buy a smaller shower really.... if your cable is to meth C then you could put a 45A breaker in I suppose.

I don't want to sound like a prat but if you're 'qualified' you really should know this.

EDIT: Didn't read the post properly sorry..... I'm going to second having a look at the connections in the shower or the shower's isolator. How do you know it was an earth fault? Have you tested it? Did an RCD blow? Was the shower on or off when it happened?

All the above still applies, mind.