Installing new electric shower, is existing cable adequate?

[peeky]

Hi all,

First post, just a quick question. My 20 year old electric shower has just died (7.5Kw) and I am considering replacing it with one of the newer more powerful (9.8Kw) models. The guy at B&Q has told me I need 10mm cable in order to install this new shower, my question is how do I tell what size my existing cable is? Is it measured across the width, the depth, the diameter of the core? I just don't know and no amount of googling has enlightened me.

Any help greatly appreciated.

P.S. The existing cable is the flat type and connected to a 30 A fuse.

Cheers.

 

[davy_owen_88]

Measure the dimensions and compare with this table:

http://wiki.diynot.com/electrics:cable_types:flatpvccables

It's probably 4 or 6mm² which is only suitable for a 9.8kw shower under very favourable conditions. I'd also bet that you don't have RCD protection and an old style consumer unit which may not be suitable for such a high load.

Can you post some pictures of your consumer unit and surrounding cables and can you also give details on the route the cable takes from CU to shower.

 

[peeky]

Brilliant, many thanks for the quick reply.

Unfortunately I reckon it's the 6mm and I'll have to settle for a less powerful shower.

Can you tell me what the CSA in the table in the link you sent stands for?

 

[RF Lighting]

CSA stands for Cross Sectional Area (of the live and neutral conductors)

for example your shower cable is 6.0mm², NOT 6.0mm diameter.

 

[davy_owen_88]

CSA - cross sectional area.

The area of each core is determined by the formula pi x (radius x radius).

 

[JohnD]

Hi Installing new electric shower, is existing cable adequate?

Nope.

 

[peeky]

Yes, you're right. It's an old (20 yrs) consumer unit with fuse wires. The shower cable travels down a plastic conduit for about 150mm, then about 6m in air (under the floor in a roomy basement) then up within the plaster of the bathroom wall for 150mm, and connects into the shower. It has 30A fuse wire protection, at the moment.
From your very helpful table I can assess that it's 6mm cable that I have.
Would I get away with an 8.7KW shower with this setup? That seems to be about the lowest power that's available now.

 

[JohnD]

Thats about 38 amps, so, no.

Also, your Wylex might not be safe to carry more than 60A in total, or more than 30A in any of the fuseways (we may be able to tell for sure if you can post a pic or say what is printed next to the main switch, and what colour it is.

Really, you need a nice new circuit, with a nice new Consumer Unit, with a nice big MCB, and an RCD for safety. The earthing arrangements at your house may also need upgrading. This will give you a noticably better shower than your old one.

If you can post a pic of the installation, showing the meter, supplier's fuse, incoming cable, consumer unit (fuseboard) and earth cables, we will probably be able to say what needs doing - it's quite a common question.

edited
http://www.diynot.com/forums/viewtopic.php?t=73320
we like pictures!
http://i113.photobucket.com/albums/n228/JohnD_UK/stickyout1.gif

 

[ricicle]

Did your man at B+Q mention that this work will be notifiable to your LABC under Part P of The Building Regulations if you are in England or Wales

 

[peeky]

As requested, here's my CU. (Don't laugh). In removing the front cover to take the photos I see it was installed in 1989. The end (black 30A) fuse, which was spare at installation, was utilised for the shower about a year later.
I hope this helps, somehow.

(NB. Re. Ricicle;
I'm in Scotland)

 

[JohnD]

Doesn't look bad, although the tails are strangely tight, and the incoming tails to the meter look very undesirable, possibly braided rubber (if so, you may be able to get the supplier to renew them free, and provide you a new earth point and maybe an isolator too). I presume the suppliers fuse is somewhere else? Is it an overhead supply?

It would be interesting to see where the earth wires come from.

that is not the brand I was expecting (I hear it's a Proteus) and i don't know if it will accept a 45A MCB. It might be possible.

the cabling doesn't look bad; you might be thinking about having a whole new CU installed, with RCBOs (if you can afford them ) for the sockets and shower. Or, cheaper, a new CU just for the shower with an RCD..

In that case, you ought to have a 100A DP isolator installed as well, as the Main Switch that cuts off your entire installation (in an emergency or for maintenance).

 

[securespark]

Proteus were based heavily on Wylex, John. That's why the proteus fuse carriers are interchangeable with the Wylex type. IIRC, they also would not accept a CPD > 30/32A unless with a 100A switch.

 

[JohnD]

do you think I can sell him some of my old MCBs?

 

[peeky]

Dear John D,
RCBO's / RCD / DP isolators??? I presume these are all modern protection systems to replace my old fuse-wire system. I'll have to do a bit of reading up to familiarise myself with modern electrics.
Funny, I've never wondered where the electric supply comes from. It first appears as you see it in the photo, coming down from the downstairs ceiling adjacent to the outside wall.
I've no idea where the supplier's fuse is located. I don't think it can be an overhead supply, though. There's no sign of electrical cables exposed anywhere outside.
I think you're right to be suspicious about the earthing arrangements. As far as I can tell, most things are earthed onto copper pipes / plumbing which all eventually lead to a PLASTIC mains supply!
You mention my supplier possibly being able to improve earthing. What could they supply?
I get the feeling that my simple 'have to replace the electric shower' is going to escalate into something a good deal more elaborate. Luckily, I know a decent electrician. Unluckily, I also know what he charges (no pun intended).
You've been extremely helpful. Thank you for taking an interest.
(Should you know of a link for 'RCBO's etc. for dummies' you may save me a trawl through Google).
Many thanks again.

PK

 

[RF Lighting]

Proteus wylex copies will definatly only allow a max of 30A per outgoing way. (I have a photo to prove it )