Shower on 4mm ring final circuit.

[Bobble23]

Hi,

I've got a customer who wants a 10.5 kW shower installed in his bathroom. As it happens he already has two unused 4mm T&E cables run from the CU cupboard to the loft. I know it's unconventional but is there any reason I can't use these cables to make a dedicated RFC for just the shower?

Thanks.

 

[Dustydazzler]

9Kw max on a 40A supply in my book.
customer needs a new cable or a new shower.
Alternatively, a "mate down the pub" to install what he has got instead of a professional electrician.

We all know it would work, but you cant document it or defend yourself it it all goes wrong.

Thinking about it...I tend to agree

My own house I would happily double up a couple 4 mm cables to make an 8mm cable if they were already there in situ and pop a 10kw shower on a B40 rcbo.

For a customer I would price to pull in a fresh 10mm cable or suggest get a lower rated shower

 

[pc1966]

Using the 2*4mm if known to be new and broadly the same length is not really an issue for me, but it really ought to be on a 45A or 50A RCBO and they are not always so easy to get (especially in compact form like Wylex).

Which itself is odd, as I imagine a lot of 10+kW showers are in use...

I would be tempted to ferrule the ends together in to 10mm ferrules so they don't end up as 10.5kW on one 4mm run though.

 

[Risteard]

Using the 2*4mm if known to be new and broadly the same length is not really an issue for me, but it really ought to be on a 45A or 50A RCBO and they are not always so easy to get (especially in compact form like Wylex).

Which itself is odd, as I imagine a lot of 10+kW showers are in use...

I would be tempted to ferrule the ends together in to 10mm ferrules so they don't end up as 10.5kW on one 4mm run though.

You can get ferrules for two cables, i.e. a 2 * 4mm^2 ferrule.

 

[davesparks]

My own house I would happily double up a couple 4 mm cables to make an 8mm cable if they were already there in situ and pop a 10kw shower on a B40 rcbo.

But 2x 4mm cables doesn't make an 8mm cable. It makes 2x 4mm cables in parallel which has a much higher current rating than an 8mm cable.

4mm clipped direct could take 37A so 2x 4mm clipped direct could take 74A.
10mm clipped direct could take 64A