Fitting a new mini trip MCB Ask questions and find answers to many subjects relating to electrics and electrical work

[bluenun]

Last week I had my old 7KW shower taken out and new 8.5KW electric shower fitted.

The electricians changed my 30 amp fuse for a 40 amp fuse in the consumer unit but it was a different brand and the little plastic door on my consumer unit does not close now.

Nothing serious but it annoys me, I was in Wickes today and they sell the same type of fuse that would allow my door to close properly but they do not have any 40amp ones, only 45amp.

Is it ok for me to put in a new 45amp mini trip MCB?

[sparx]

hi,
possibly, but it depends on size of the cable, how its run, distance, ect,
the certificate they MUST legally have given you will say what size of cable, type of MCB , earth loop impedance ect. so repost with details & will try to be more help,
if they didn't give a cert. then they also won't have registered the job as required so I would call them back, tell them you want the correct MCB & ask for cert. (at least 'Minor works')
regards SPARX

[ericmark]

As Sparx says not quite as easy as quick swap. There are both different sizes of cable and different types although they look the same at quick look so the paper work will most likely say if 6 or 10mm and also a number like 6242Y the last letter is important as type or words like PVC also the route but on minor works often this is missed and it may not have the information you require. Although you may have it from the last inspection and test which has a little more on it to the minor works. May be a lot easier to get right size? Also note the letter before the number i.e. B40 that letter makes big difference to how quick it will trip and you need to get same.

[bluenun]

It is a 6mm cable. I live in a bungalow and the consumer unit is in the hallway next to the bathroom so I guess the length of cable is under 2 meters in length.

I did not know I was supposed to get a certificate and they certainly did not mention or offer one. How annoying to find out now.
So I do not know anymore details.
They left a right mess here and I would definitely not use them again.

As the shoer is working fine perhaps I should just put up with the consumer unit door not closing.

[ericmark]

We would normally consider 6mm cable as 32 amp. There are types that can take more but I would not recommend exceeding 32 amp unless you knew what you were doing. So may be the 40 amp is OK I could not say they were wrong but lack of paperwork would ring alarm bells with me.
There are basically three types of paperwork that can be raised. Minor Works if all they did was upgrade something that existed i.e. replace shower with bigger one and change the MCB. If however they started from scratch then an Electrical Installation Certificate would be required which contains more information and has two forms one with multi-signatures and one with single signature. If you live in England or Wales a copy will also be sent to the building control either direct or through clearing agent and you need to have your copy within 30 days. Failure could affect your insurance cover. You really do need to pester for it. Read the projects and links to find out more.

[bluenun]

OK I think it is making a bit more sense to me now after reading your last post.

Because I have a 6mm cable I should not consider changing my current 40amp fuse for a 45amp fuse.

If I had a 10mm cable it would be ok to do so.

It is a shame my local Wickes do not sell 40amp fuses.
So I either leave it as it is or try to find a 40amp fuse that will allow my consumer unit door to close.