Electric Shower Cable Size

Sleeper12

Hypothetical question:
Electrician installs electric shower. He does his calculations & deems 6mm cable suitable. Cable runs the depth of the house from front to back in the attic. so lets say 25 or 30 foot. It's lying on 100mm attic insulation.

My question is: if the homeowner later decides to get 200mm attic insulation laid on top of existing insulation & shower cable should the cable be upgraded to 10mm or would the extra insulation make very little difference to the cable size. I'm not looking for exact answer but a more rough rule of thumb

2011

The cable will have to be derated to account for the fact that it will not be able to cool as easily as before. This is likely to mean that a larger cable is required. Once ambient conditions become less favorable the cable sizing should be reviewed.

2011

Current carrying capacities provided in ET101 only apply for particular ambient temperatures (this is stated in the regulations).

Interesting at work we had to carry out thermal analysis on a number of cables that are to be immersed in fast moving cold water. This meant that we could pass a far larger current than is normally possible for a cable of this size without any heating or impacting on the integrity of the cable.

Joe1919

You could always leave a foot or two of slack in the cable so it could be pulled up over insulation. The link below (British Standards?) may answer your question? It does appear from below that the current carrying capacity of 6mm cable ( with 100 mm of insulation) can in certain situations reduce from 34 amps down to 27 Amps with large (440mm) amounts of insulation.

http://electrical.theiet.org/wiring-matters/15/current-ratings.cfm?type=pdf

Sleeper12

Thanks for the replies. I'm coming across attics like this maybe twice a month. I'm not an electrician but would like to be able to offer the best advice possible.
Im assuming I should suggest that they get in an REC. Should I suggest asap or should I suggest next time they have an REC in to get it done?

Dardania

It's covered under the SEAI Better Energy Homes guide for attic insulation that the installer should check details like this.

Of course, getting attic insulation (solely) under that scheme is overkill in my opinion...

Calahonda52

Dardania wrote: »

It's covered under the SEAI Better Energy Homes guide for attic insulation that the installer should check details like this.

Of course, getting attic insulation (solely) under that scheme is overkill in my opinion...

Can you get a link to this document as the one I see, attached, makes no reference to cables.

Dardania

Calahonda52 wrote: »

Dardania wrote: »

It's covered under the SEAI Better Energy Homes guide for attic insulation that the installer should check details like this.

Of course, getting attic insulation (solely) under that scheme is overkill in my opinion...

Can you get a link to this document as the one I see, attached, makes no reference to cables.

See page 35, item j.:

http://seai.ie/Grants/Better_energy_homes/contractor/Code-of-Practice-Rev-7-1-2016.pdf

Calahonda52

Joe1919 wrote: »

You could always leave a foot or two of slack in the cable so it could be pulled up over insulation. The link below (British Standards?) may answer your question? It does appear from below that the current carrying capacity of 6mm cable ( with 100 mm of insulation) can in certain situations reduce from 34 amps down to 27 Amps with large (440mm) amounts of insulation.

http://electrical.theiet.org/wiring-matters/15/current-ratings.cfm?type=pdf

The certain conditions here, for the lab test refer to the cable being in certain fixed positions and not when randomly "strung across" ceiling joists as is sometimes the norm.

Dardania

RE current carrying capacity We're probably saved by something 2011 referred to (BTW that water cooled cabling idea sounds very cool!)- lower ambient temperatures in the attics, and the likeliehood that many people take their showers when the attic is cool. Also, how long do people actually shower for versus the thermal rise of the copper...

Joe1919

Dardania wrote: »

See page 35, item j.:

http://seai.ie/Grants/Better_energy_homes/contractor/Code-of-Practice-Rev-7-1-2016.pdf

j. It is essential that any heavy-duty cables (e.g for cookers and showers) are not covered by the insulation material and should be left on top of the new insulation, provided there is sufficient slack to do so. Where this is not possible, a gap of at least 75mm should be left either side of the (heavy duty) cables for the entire length within the attic area.

You are spot on I think. I think this is especially important with 6mm cable as this size is possibly underrated in some circumstances, as when more powerful showers are fitted and 10 mm cable might be the preferred choice.

The Sidewards Man

2011 wrote: »

Current carrying capacities provided in ET101 only apply for particular ambient temperatures (this is stated in the regulations).

Interesting at work we had to carry out thermal analysis on a number of cables that are to be immersed in fast moving cold water. This meant that we could pass a far larger current than is normally possible for a cable of this size without any heating or impacting on the integrity of the cable.

Similar to overclocking a CPU, this is well known. Not making any break through here.

Stoner

The Sidewards Man wrote:

Similar to overclocking a CPU, this is well known. Not making any break through here.

MOD note

Sidewards Man. Nobody is talking about making breakthroughs, it's discussion forum. The point was relevant to the OPs post and offered advice. We all understand that water cooling has been used for 1000's years.
It's not a competition. Read the charter relating to one upmanship before posting again please.

If you want to discuss this further please take it to PM so as not to derail the thread.
Thank you.

2011

Joe1919 wrote: »

You could always leave a foot or two of slack in the cable so it could be pulled up over insulation.

+1

Good idea.