How Do I Identify The Size Of Cable (e.g. 6mm, 10mm, 16mm)?

jelnet · 26 Feb 2010

Hi folks

I'm in the process of upgrading my shower to a 10.5kW version, and from what I can gather on here I need at minimum a 10mm2 cable connecting it to the consumer unit.

However I'm baffled as to where this measurement is taken. The present cable is in some places white and others grey and is kind of rectangular and about 6mm on it's thinner side and about 12mm on it's wider side. Does that mean it's 6mm cable?

How do you measure it and work out it's size?

Thanks for any help!

londonboy · 26 Feb 2010

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

jelnet · 26 Feb 2010

Brilliant thanks londonboy!

rebuke · 26 Feb 2010

If it's white in some places, and grey in others that implies there's a joint somewhere - you need to identify where it changes as any connections may have a lower capacity than the cable itself, so might be the limiting factor.

Ideally with a high power appliance like a shower, the only joint should be at the isolator (often a pull cord one) - it's not against the regs to have other joints, but it adds more potential for things to fail, and they need to be rated appropriately...

londonboy · 26 Feb 2010

Remember there is a lot of variables, longer runs, insulation, grouping etc can all result in you needing a bigger cable. Also you need RCD protection.

I'd recommend getting an electrician round to double check everything (before you fit the shower and tile the wall

).

jelnet · 26 Feb 2010

There is an isolator switch for the shower in the airing cupboard in the kitchen (ie. not in the bathroom and not a pull cord). It's one of those standard white box white switches with a glowing red light. I'm not sure if that meets "regs". I think you're right though I'd need to get an electrician in to replace the wire. Also I have an old style fuse box (not sure if I have RCD's whatever they are) so not sure if that's suitable.

Ta for all your advices!

FrankE · 26 Feb 2010

You should assume it's a 6mm sq (edit: and therefore needs replaced with a bigger suitably sized cable) as for the old shower I wouldn't expect anyone to supply and fit a considerably more expensive and little harder to work with 10mm sq when a 6mm sq was suffice.

The regs are the IET wring Regulations, currently the 17th edition British Standard 7671, effectively legally binding.

Any circuits supplying equipment in a room with a fixed bath or shower (ie a bathroom) must be protected by an RCD.

Your property, life and limb is at risk if you do not use the correct size of conductor so I would also advise you get an electrician to check it out.

ban-all-sheds · 26 Feb 2010

londonboy said:
//www.diynot.com/wiki/electrics:cable_types:flatpvccables

jelnet said:
Brilliant thanks londonboy!

Taylortwocities · 26 Feb 2010

FrankE said:
The regs are the IET wring Regulations, currently the 17th edition British Standard 7671, effectively legally binding.

Well, you are wrong there. BS7671 is not statutory (ie it is not legally binding)

Building Regulations Part P is, however. And you will need to comply with all of that. It refers to BS7671.

Please refer to the WIKI and read up on the legalities of what you are thinking of doing.
IMO (as you don't know what an RCD is) you should get a registered electrician in to:

assess your installation to see if it can stand the extra load
look at the existing wiring to see if it is big enough for the extra load
tell you about the important safety measures that you MUST take when mixing electricity with water.

You can get someone by looking at www.competentperson.co.uk

FrankE · 26 Feb 2010

That's why I said effectively, because the Buildings Regs make it effectively a legal requirement to follow the regs.

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How Do I Identify The Size Of Cable (e.g. 6mm, 10mm, 16mm)?

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