6mm or 10mm - that's the question!

[Gert_Lush]

I'm about to install a 10.5kW shower about 12m from my consumer unit.
I know i can get away with using 6mm cable provided it does not exceed a particular length (which it doesn't) and it is clipped. Question is, does it have to be clipped at regular intervals along its entire length, or just a percentage of its length? I can easily clip the section of cable that will pass through the loft, which will be about 60% of the run, but the rest will be dropped down inaccessible walls so i won't be able to clip those sections. Is this satisfactory, or am i going to have to resort to using unclipped 10mm?

I'm keen to do all the labour intensive work myself before calling in the pro's to get it the Part P tick in the box.

Cheers.

 

[dingbat]

The length is insignificant in this context. You need 10 sq mm because of the continuous current you will be drawing.

Clipping (unless it is to an insulating surface) does not affect current-carrying capacity, but all cables should be properly supported in any case.

As for getting it retrospectively certified and notified by a registered electrician, I wish you luck. I wouldn't do it. There is no worthwhile income to be had in signing off work done by DIY-ers... unless you're prepared to stump up half a day's labour for the service.

 

[Adam_151]

use 10mm² , its possible that 6mm² might scrape by if its clipped direct and no derating factors have to be applied, but this is unlikely, and it'd be close anyway, use 10mm²

 

[1974stephen]

For the additional cost in cable (approx. £5) there is no doubt that you should install 10mm2. Just think in three year stime when your shower breaks and you want a nice new one that just that little bit too powerful for 6mm2? How gutted will you be you saved that £5 previously?

 

[ban-all-sheds]

Is this satisfactory, or am i going to have to resort to using unclipped 10mm?

10mm² cable still needs to be clipped, just with slightly greater spacing than 6mm². And as it's heavier, be very wary of long, unsupported vertical drops.

I'm keen to do all the labour intensive work myself before calling in the pro's to get it the Part P tick in the box.

I cannot stress strongly enough that you must find your pro first, and get his agreement about what you are doing. Complying with Part P is not a formality, and involves a great deal more than a tick in the box.

 

[PJP]

so what is the maximum run for 10mm^2 cable from c/u to shower?

mine is 16m...also how many bends?

 

[TopTrumper]

Look at the terminals in the shower for cable requirements, ie: 9.5 and over has to be 10mm because of csa going to element..
as a rule of thumb i use 6mm for 7.5 and maybe a short run on a 8.5.
10mm for anything else. although even taking the showers csa into consideration its always gonna be 10mm with voltage drop..

 

[Big_Spark]

A 10.5kW shower will draw a constant current of 45.6A at 230V (Which is the voltage you MUST use for your calculations).

If you check out Table 4D5A you will see that even 10mm² only has a rating of 47A when installed in an insulated walls, and the types of walls described are likely to be insulating..if not directly containing insulation. Further you must take into account the temperature fluctuations that will occur in any loft space as the ambient temperature changes. These factors must be taken account of when deciding on cables sizing.

Personally I would be tempted to up the cable to 16mm² T&E, or use 3 core 10mm² SWA. The third core being the Earth rather than relying on the SWA for the earth path. T&E would be easier though.

 

[baldelectrician]

10mm

If it's done in a lesser size the manufacturer (in the shower fails under guarantee) may say the shower has not been installed to manufacturer's instructions therefore your guarantee is void