Home electrical question

[HarryHornby]

Oh font of foccer knowledge....


We've got an electric shower in our bathroom and we've had a rather lucky escape so it would appear.  The ceiling switch jammed, and being silly I just left it, several weeks later there were burn marks on the outer plastic, looks like it overheated and melted the insulation on the cables as well.


I want to get the shower up and running again but need to cut the cables back to good cable.


1 cable has enough slack, so I can cut that one back but the other needs cutting back and then extending because there isn't any slack.


I've got some 6mm twin and earth to replace the cable, a new 45amp double pole ceiling switch and a junction box to join the cables.


The max ampage junction box I can find in toolstation etc is 30amp, will that be ok?  I need to be sure it's safe because it's going up into a ceiling void and I really don't fancy a fire (we've dodged that bullet already).


Ta muchly

[esetest]

What size shower do you have , if its 9kw or bigger , then it should be wired in 10mm cable , it is quite common for the pull switches to burn out , it is good practice to switch them off when not in use , as it reduces the chance of them arching out .
Rather than use a standard 30A junction box , get a 150mm by 150mm plastic adaptable box from an electrical wholesaler , and get 50A rated terminal blocks , just make sure the junction box is accessible for future inspection , i would preferably use through crimps if you have a suitable crimping tool .

[fazersharp]

Yes I agree with esetest, re the question on shower Kw 6mm cable may not be big enough.
I think the issue with junction boxes and the A rating is more to do with the size of the terminals inside and the available space in the box to bend and position 10mm/6mm cable.   

When you say the switch jammed would that mean that perhaps a piece of metal inside has come away and leading to the shorting causing the burnout. I dont see how just being on would cause an issue unless the cable is the wrong size for the shower. Mine is 10mm for a 9Kw shower and also no part of the cable in the attic lays under insulation.

[HarryHornby]

OK, shower is 8.5kw, found a label underneath.


The shower was already installed when we bought the house.


re situation with cables running through insulation this is why, the house is like a challet bungalow, except it's a house, but we do have chalet bungalow style bits out the roof.  This bathroom was oringinally a storage room when built.  LIke other houses in the close this room was converted into a bathroom in the '80s.


The main cable runs through the walls up into the void with flat roof (fibreglass job, not felt) above and bathroom ceiling below , the gap is about 150mm.


The reason it runs in this void is to allow for the ceiling switch.


Existing cable is 6mm twin and earth running back to it's own 30amp fuse in the circuit board.


re turning the ceiling swith off, yes, we would always do that but someone ( a child) yanked on it and it wouldn't return to off, the LED was permanantly lit and when the chord was pulled it did nothing.  It was silly of me to leave it like that, I know. :-(

[fazersharp]

So to get this right in my mind you have a "normal " attic space but also a dormer with that space between ceiling and flat roof being 150mm. If this is so I would perhaps cut the cable at the point in the normal attic space and join it their for easy access and inspection and run the new cable as one piece through the 150 gap so there is no junction boxes in this space which I assume is also filled with insulation.

DISCLAIMER --- I am not an electrician. And to the letter of the law I dont even think you are allowed to mess with stuff in a bathroom yourself.

[HarryHornby]

Yes that is correct in terms of me having an attic and a dormer but the cable for the shower doesn't go anywhere near the attic, it runs in the voidthat's the overhang infront and below the Dormer then up the wall (inside the void, no insulation) and into the void between the dormer roof and celiing).


From what I can work out, the cable then runs 1m (if that) through the void with insulation to the ceiling mounted switch and then about another 1m from the switch to another void that's been created where the shower is fitted, am assuming there is a void there, prob not deep, but a void all the same to take the cold water feed for the shower.


So in theory there is only about 2m of cable (6mm) in the void with the insulation.  I've had to make a hole in the ceiling to get to the cables (the whole in in what used to be the airing cupboard and is now just a cupboard so it can't be seen).  Because it's not seen I can leave the new junction box out of the void and just have cables up there.

[fazersharp]

So in theory there is only about 2m of cable (6mm) in the void with the insulation.  I've had to make a hole in the ceiling to get to the cables (the whole in in what used to be the airing cupboard and is now just a cupboard so it can't be seen).  Because it's not seen I can leave the new junction box out of the void and just have cables up there.

That sound ok to me. The bit about not having the cable under insulation (I think ) is just best practice and one of those "when practicality allows" grey areas

Dont forget to use the old cable to pull the new one through

[Grayo]

6mm cable is 60 Amp rated cable. A 8.5Kw shower will draw 35.42 Amps on full power so 6mm cable is fine as is the 30 Amp fuse.

[HarryHornby]

Is it ok to use the yellow (6mm) Butt Connectors to join the two (twin and earth) cables?  And do you just squish together with normal piliers?

[Grayo]

6mm butt connectors will be ok but crimp them with the proper crimping tool as normal piers are likely to cut through them. Tape them up with insulation tape once you've crimped them. If you don't have a crimping tool then I would use connector blocks instead of butt connectors.

[HarryHornby]

Thank you, I was looking in toolstation for a 50A terminal blocks but can't find any.  Will get some of the 6mm butt joints, a crimper and a straight junction box to keep them all in once crimped.


Although.... once last question, promise.


Looking in toolstation - item number 44708 or 16740  is that what I need?

[fazersharp]

I would go for the bigger one to make your life easier when dealing with fat cables. Dont think it need to be ip rated though - but wont hurt either imo

[esetest]

As a qualified electrician with over 34 years experience , and a Niceic approved contractor , 6mm sheathed flat cable will not carry 60A , the maximum rating from table 4D5 of the requirements for electricians is 47A reference method C clipped direct , it is 34A reference method 100 above a plasterboard ceiling covered by thermal insulation not exceeding 100mm in thickness . Replacing a damaged cable is not notifiable but using the junction box would make it so .
As it is a 8.5kw shower you will get away with the 6mm cable .
If you go down the route of getting  an electrician in and having it notified  , you may need to have an 30mA  RCD  installed and the protective bonding  upgrading  , this will be expensive .
I would join the cable as previously stated , and categorically deny having any electrical work done if you have to make an insurance claim  .

[HarryHornby]

cool, loads cheaper than a pair of crimpers :-)


Cheers for all the advice.  I get nervous around things I don't know a lot about.  I can use a screwdriver and tools to do things but always like to make sure I'm doing it as right as I can.


Idealy I would rather not extend the cable, I would rather run a new one but that would mean taking the whole shower enclosure down :-(


If I have to bodge it I want to bodge safe!  :-)

[esetest]

If you have a Denmans electrical wholesalers nearby they sell to the public you can get 50A connector blocks there . The yellow butt connectors or through crimps will be fine , but I would use a crimping tool rather than pillars due to the heavy load .

[Grayo]

I would go for the bigger one to make your life easier when dealing with fat cables. Dont think it need to be ip rated though - but wont hurt either imo

IP ratings are "Ingress Protection" ratings and are used to identify the effectiveness of keeping out moisture and dirt, etc. As you say, not necessary in this case.

[fazersharp]

As a qualified electrician with over 34 years experience , and a Niceic approved contractor , 6mm sheathed flat cable will not carry 60A , the maximum rating from table 4D5 of the requirements for electricians is 47A reference method C clipped direct , it is 34A reference method 100 above a plasterboard ceiling covered by thermal insulation not exceeding 100mm in thickness . Replacing a damaged cable is not notifiable but using the junction box would make it so .
As it is a 8.5kw shower you will get away with the 6mm cable .
If you go down the route of getting  an electrician in and having it notified  , you may need to have an 30mA  RCD  installed and the protective bonding  upgrading  , this will be expensive .
I would join the cable as previously stated , and categorically deny having any electrical work done if you have to make an insurance claim  .

There you go proper advice from a real lecky. I like you when doing stuff like to make sure I am doing it to the book and thats why i know some stuff.
Perhaps his bonding is already to spec--- are we talking 6mm upgraded to 10mm

[esetest]

His protective bonding may be adequate , it may be undersized , or he may not have any protective bonding at all  , he may not even have a means of earthing , he might not have 30mA RCD protection for circuits in a bathroom or cables in wall and voids . The Ip ratings are for ingress protection of moisture or solid objects into electrical enclosures , the first number is solid objects the second number is moisture .providing the Junction box is out of the zones  , it will only need to have Ip4x protection against objects no bigger than 2mm in diameter . Just do a temporary safe joint , and when you are redecorating , upgrade to a new cable . With adequate protection.

[HarryHornby]

OH FFS, why is nothing simple?? ha ha


Just got that box, but has standard connectors and there is no way I'm getting 2 of each cable into one of those.


I will speak to our sparks guys at work and see if I can borrow some crimpers and maybe blag some 6mm butt connectors.  I don't really want to spend £16 on crimpers I will use once.


At least I now have a nice little plastic box to put it all in once it's crimped. 


The work was done in the late 80's so bonding and all that prob way out of date.  It does go back to it's own 30amp fuse separate from the main board though.  Not RCD though.


The plan is to get the bathroom ripped out at somepoint but that's money allowing, will prob be in 2 years.  Then we are re-wire properly :-)  I say we, I mean whoever fits the bathroom.