shower 6mm or 10mm cable?

sgun

We are having a new shower and want to fit a 9kw. How can we tell if the cable is 6mm or 10mm? The old shower was fitted in 2010 so it should be 10mm but obviously we don't want to risk it if it is only a 6mm cable. The cable run is quite long - just under 20m and through uninsulated walls but under loft insulation (we are going to try to get it lifted out). The earth is stranded rather than solid if that makes any difference?

Risteard

It will be marked on the sheath.

Also a 6mm^2 T&E cable has stranded live conductors but a solid cpc, whereas a 10mm^2 T&E cable has stranded live conductors and a stranded cpc.

So the stranded cpc will suggest that it is a minimum of 10mm^2 - although you should still verify this by reading this on the cable sheath.

cognoscenti

If you can get at some in the fully-enclosed state either before it enters your shower or in the loft, 6mm cable usually measures approx. 13.5mm wide in total as opposed to 10mm which usually measures approx. 17mm total in width.
AFAIK 10mm Twin&Earth has a stranded earth & 6mm does not but whether that is always the case I'm sure a more knowledgable person will soon say. 

When I upgraded mine I found a lot of debate re: 9kW & 6mm cable with lots of  "or depends" type comments with the usual "yes" and "no" answers.
Mine is however a much shorter run and so far - after some years - I've not had the slightest hint of a problem on 6mm cable with (currently, forgive the pun) the second 9kW shower in those years.

sgun

The width is approx 15mm which doesn't help! Back up into the attic tomorrow to see if I can find markings on the sheath. I didn't spot any last time I was up there but I wasn't really looking for them. I have a feeling that 9kw would be fine on 6mm as neither of us has long showers but I'd rather be safe than sorry.

adonis

sgun said:

The width is approx 15mm which doesn't help! Back up into the attic tomorrow to see if I can find markings on the sheath. I didn't spot any last time I was up there but I wasn't really looking for them. I have a feeling that 9kw would be fine on 6mm as neither of us has long showers but I'd rather be safe than sorry.

Stick with cold showers and you will be fine,

and save on the electricity bill.

bris

20m run is pretty long and it being under insulation doesn't help. If you can, upgrade to 10mm and fit a 10.5kw shower. With 10mm spend a little extra on the shower, the difference isn't that much.

grumbler

I don't see why the length can be of any importance. Insulation - possibly, but not the length.

Ectophile

grumbler said:

I don't see why the length can be of any importance. Insulation - possibly, but not the length.

Voltage drop along the cable.  Though I don't think it would be excessive over 20m even with 6mm2 cable.

FreeBear

A useful table for

Ectophile said:

grumbler said:

I don't see why the length can be of any importance. Insulation - possibly, but not the length.

Voltage drop along the cable.  Though I don't think it would be excessive over 20m even with 6mm2 cable.

A useful table for you - https://www.tlc-direct.co.uk/Figures/Tab4.7.htm

A 9Kw shower on 6mm² cable will have approx 5.7V drop on a 20m run whilst a 10mm² cable will only have a 3.4V drop. But it is the current carrying capacity that is more important. If the cable is undersized, it will overheat and you run the risk of a fire. You really don't want to be using a 9KW shower on 6mm² cable as it exceeds the max current rating in most installations.

Leave it to a qualified electrician - Fitting a shower is a "notifiable work" and must be signed off with certificates provided.

avoidtheupsidedownbottles

FreeBear said:

A useful table for you - https://www.tlc-direct.co.uk/Figures/Tab4.7.htm

I wonder why voltage drop is stated as being lower for 3 or 4 cores compared to 2 core  

grumbler

Ectophile said:

Voltage drop along the cable.  Though I don't think it would be excessive over 20m even with 6mm2 cable.

Yes, but it's not really a 'risk'. The shower will lose some power.

Resistance of 20m  of 6mm cable is just 0.13 Ohm compared to 0.076 Ohm of 10mm cable and  6.4 Ohm of 9 kW shower.

Loss of power is approx. (0.13-0.076)/6.4=0.8%