8.5 kw shower cable size

scottg · Posted: Sat Nov 15, 2008 9:19 am

can i fitt 8.5 kw shower using 6 mm2 cable 3m from mains board
only thing is its going through loft insulation more than 100mm
would it be ok to use trunking with insulation on top would this effect cable calculations

TopTrumper · Posted: Sat Nov 15, 2008 9:30 am

A whole 3 metres?
yes 6mm will be fine

GaryMo · Posted: Sat Nov 15, 2008 10:26 am

6mm through loft insulation greater than 100mm is rated at 27A (method 101#).
Your 8.5kW shower is rated at (8500/230) 36.96A.

The current carrying capacity of the cable in its installed conditions must be at least the rating of the device it's supplying.

Can you reroute the cable away from the insulation? Clipped direct (method C) with no insulation is rated at 47A.

GaryMo · Posted: Sat Nov 15, 2008 10:27 am

TopTrumper wrote:

A whole 3 metres?
yes 6mm will be fine

How did you come to that conclusion?

TopTrumper · Posted: Sat Nov 15, 2008 8:01 pm

GaryMo wrote:

TopTrumper wrote:

A whole 3 metres?
yes 6mm will be fine

How did you come to that conclusion?

EASY

PS, im sure the OP understood every word you just said.
Are you seriously trying to say 6mm cable for a 3 metre run is not suitable?

GaryMo · Posted: Sat Nov 15, 2008 8:06 pm

Maybe it's you who didn't understand anything I said?

Easy as in you guessed without looking at table 4D5?

scottg wrote:

can i fitt 8.5 kw shower using 6 mm2 cable 3m from mains board
only thing is its going through loft insulation more than 100mm
would it be ok to use trunking with insulation on top would this effect cable calculations

Are you seriously trying to tell me that a 6mm cable with a rating of 27A, given its installation method is good for a design current of 36.96A?

I sincerely hope not!

TopTrumper · Posted: Sat Nov 15, 2008 8:46 pm

GaryMo, fair enough, point taken.
Answer me one question, if the OP had said he wanted to install this shower, what cable would you advise him for the 3 metre run?

http://www.alertelectrical.com/Electric-Power-And-Mixer-Showers/Mira-Showers/Mira-Electric-Showers/Mira-Vie-108kw-Electric-Shower-Satin-Chrome-D62127.asp

GaryMo · Posted: Sat Nov 15, 2008 9:02 pm

I would advise 10mm and keep the cable away from thermal insulation.

Another example of why electric cables and thermal insulation don't mix.

TopTrumper · Posted: Sat Nov 15, 2008 9:07 pm

GaryMo wrote:

I would advise 10mm and keep the cable away from thermal insulation.

Another example of why electric cables and thermal insulation don't mix.

Never mind what you would advise him to do,he has already stated
"It is going through loft insulation"
So what cable would you say in your expert opinion, does the OP need for this 3 metre run?

TopTrumper · Posted: Sat Nov 15, 2008 9:13 pm

GaryMo, to help you along a little, here is the instruction manual for the said shower.

http://www.mira-showers.co.uk/onlinecatalog/pdf/p1088848_w2.pdf

I would like you to take particular notice to page 9, to help, I will quote you a paragraph,

The terminal block will not accept cable larger than 10 mm2.

So as we are looking at tables, what do you say?

GaryMo · Posted: Sat Nov 15, 2008 9:18 pm

Well, if the terminals won't accept a conductor larger than 10mm then 10mm is the maximum cable size for that given shower.
So, either change the shower, remove the insulation or re-route the cable.

It's not rocket science is it?

TopTrumper · Posted: Sat Nov 15, 2008 9:29 pm

OK.
Lets assume that the insulation cannot be moved, and there is no other route whatsoever, would you install the 10mm cable?

GaryMo · Posted: Sat Nov 15, 2008 9:31 pm

I wouldn't install a 10.8kW shower, that's for sure!
10mm in those conditions is rated for a maximum of 36A.
A shower would need to be purchased rated at less than 36A, 8kw maximum.

TopTrumper · Posted: Sat Nov 15, 2008 9:36 pm

GaryMo wrote:

I wouldn't install a 10.8kW shower, that's for sure!
10mm in those conditions is rated for a maximum of 36A.
A shower would need to be purchased rated at less than 36A, 8kw maximum.

So lets get this right,
if you turned up at a clients house, and they presented you with this shower and there preferred cable route, and the fusebox was 3 metres away, you would tell them your not installing it?

GaryMo · Posted: Sat Nov 15, 2008 9:48 pm

They would need to take my professional advice.
I would recommend an alternative route thus avoiding insulation. If that's not possible then I would inform them that I could install a 10mm cable but it's only rated at 36A and can only supply a shower rated at a maximum of 8kW.

I would NOT install a shower with a rating higher than the current carrying capacity of a cable.

Why is this so difficult to understand? It's like asking me to put a square peg in a round hole - something has to give.