wire up shower to consumer unit

[mickey mouse]

I rewired the light in my bathroom and it blew twice before I realised I'd wrongly connected it. It's okay now but I am about to wire in an 10.5kw shower and I plan to get that right first time. So can you give me some advice?

I am planning to have a single 10mmsquare cable from the 45A mcb in box to the shower, with the big red switch cut into the cable halfway along, outside the bathroom door. The switch just says L & N Supply, L & N Load, plus the earth, so I would connect the load side to shower and supply side to box, and earth the switch back to the consumer unit. It seems to simple. Any ideas?

 

[steve190]

Yes.

Have you considered the need for suplementary bonding. Is it fitted? If so is it correct and what else do you need to do.

 

[fido]

Make sure all the screws for the cable terminals are good and tight or you can get sparks / heat at them.

 

[mickey mouse]

Does the supplementary bonding mean extra earthing? I found the 'how to do it pages' here and that confirms [I think] that I'm doing it the correct way - it is much simpler than the lights because it is really one cable running from the supply unit to the shower unit with the switch in the middle.

I realise I have a choice to move all the mcbs along one space to fit the new 45 mcb or put in [tails with a new small box?] but as I once already disconnected everything I think I will opt to do that again, as I dont have much space for new stuff in the wall where the gubbins is all sited. Plus there's ne need to spend extra cash.

I have read about RCDs but I dont see how they apply here? I dont really understand how they work on an electric lawnmower either.

Anyway my 10mm cable is the older oval type and it is such a bitch to get it into the metal box x 2. I have put 3 mm alu sheath over about a 6" length of the run where the cable is notched through a stud, to protect from people nailing and screwing into it. but after the short bit the cables then fall away into the partition. The wall is not insulated but there are a couple of notches the load passes through.

I have another question: don't the building regs now say that from 2005 all new electrical work must be done or passed by an approved sparky. How easy is it for a spark to check things like this in retrospect. I would like to get a trustworthy spark in to assess the rest of our elec cos some of it is a bit doubtful.

I tightened the connections up several times as I found the movement involved in getting in the last cables made the first lot a bit looser. Trouble is there is hardly any scope to get the switch plate well off the wall now its connected as there's hardly any play on the cable. This will make it difficult when it comes to painting the wall. Should I disconnect and put in longer lengths? How much of the grey outer sheath can I strip off from the cable once it comes out the metal box? Thanks for the replies.

 

[fido]

Depending on the design of your MCBs they might not need to be slid off the end of the consumer unit DIN rail. Some have a clip that can be retracted and the MCB lifted off. The grey insulation must go into the box or consumer unit. The individual red and black wires should not be visible when switches / covers etc are in place.

 

[ban-all-sheds]

Does the supplementary bonding mean extra earthing?

That's a way of looking at it, but that's not actually what it is. However, provided you do it the way that you see it described then it doesn't matter what you call it.

I realise I have a choice to move all the mcbs along one space to fit the new 45 mcb or put in [tails with a new small box?]

Splitting the tails and putting in a separate mini-CU will require you to pull the main service fuse to isolate the entire supply, not something that you should be advised to do....

I have read about RCDs but I dont see how they apply here?

They apply here because it is generally considered to be a Good Thing™ to have RCD protection on a shower, given its combination of a high-current supply, water and nakedness....

I dont really understand how they work on an electric lawnmower either.

Whether you understand how they work or not is irrelevant - if you've got an electric lawnmower then you really, really should only use it on an RCD protected supply. I'm guessing from what you've said that your CU has no RCD in it, so none of your sockets have RCD protection. This is a Bad Thing™, and should be rectified. In the meantime, please get plug-in RCDs for your lawnmower/strimmer/hedgetrimmer/garden vac etc etc.

Anyway my 10mm cable is the older oval type

Err - what do you mean by "older type" - all twin and earth cable is oval...

and it is such a **** to get it into the metal box x 2.

Yup.

I have put 3 mm alu sheath over about a 6" length of the run where the cable is notched through a stud, to protect from people nailing and screwing into it. but after the short bit the cables then fall away into the partition. The wall is not insulated but there are a couple of notches the load passes through.

Firstly, I'm not sure that aluminium will provide sufficient protection - it's pretty easy to nail through. Secondly, please check here for info on where your cable is allowed to run, in case it needs mechanical protection over its entire length.

I have another question: don't the building regs now say that from 2005 all new electrical work must be done or passed by an approved sparky.

Basically done by, not done by you and passed by one, although the implementation of the notify-to-BC route varies considerably from one LA to another. Do a search here, at Screwfix ( http://www.screwfix.com/talk/forum.jspa?forumID=23 ) and at the IEE forum ( http://www.iee.org/Forums/forum/categories.cfm?catid=205&entercat=y ) for Part P.

How easy is it for a spark to check things like this in retrospect.

Not easy enough to make it a lot cheaper than having an electrician do it all in the first place, and also please refer to what I said above about how you are able to comply with the new requirements of the Building Regulations. Basically you will not be able to find any registered electrician prepared to say that he did the work when he didn't, so you're left with the notify-BC-in-advance route. When you do that you'll find out how your particular one has decided to handle non-self certifiable work.

I would like to get a trustworthy spark in to assess the rest of our elec cos some of it is a bit doubtful.

As ever, personal recommendation is the best way to pick a reliable tradesman, but whatever you do, you need to get a few quotes for what's called a Periodic Inspection Report.

I tightened the connections up several times as I found the movement involved in getting in the last cables made the first lot a bit looser. Trouble is there is hardly any scope to get the switch plate well off the wall now its connected as there's hardly any play on the cable. This will make it difficult when it comes to painting the wall. Should I disconnect and put in longer lengths?

If the cable is already installed, that means replacing it - you can't add to it. And if you have more cable, how will you then get the switch plate back? Excess 10mm² cable is a b*gger to stuff inside a box....

How much of the grey outer sheath can I strip off from the cable once it comes out the metal box?

As much as you like, once its entered the box. And don't forget to use grommets on the holes where it goes in.

 

[securespark]

a high-current supply, water and nakedness.....

Sounds like my idea of a good weekend..

 

[ban-all-sheds]

I take it you've not seen me naked....