Wot size cable for a 10.5kw electric shower?

[FlyingScotsman]

Away to fit a 10.5Kw electric shower. I have an isolation switch which will go outside the bathroom on the wall and I have a RCD rated at 50amps for inside the mains electric box.

Question is what size of cable should I use - seems either 6mm or 10mm is suggested but 10mm is HUGE and would expect it to be hard to work with.

Advice please.

Thanks.

 

[Sparky Jim]

The size of the cable is dependent on several things Scotsman, and one of these is distance from the consumer unit to the shower. However no matter which way you work this out, 6mm is far too small fr what you want to do. The current pulled by the 10.5kW shower is over 45A and if you check the Regs book or an Onsite guide, you will see that the maximum current carrying capacity of a 6mm T&E is 42A. However, depending on many other factors, you could, in theory at least, need to use 16mm, although I do feel this extremely unlikely so please do not start to panic just yet.

 

[ban-all-sheds]

the maximum current carrying capacity of a 6mm T&E is 42A.

Reference Method 11 or 13 - 51A
Reference Method 1 - 46A

But I agree - do not consider using 6mm² cable.

 

[Sparky Jim]

As I am new to this forum I have no wish to get into an argument with you Ban-all-sheds, however the reference method you use is not applicable in a domestic setting and therefore not applicable to this discussion. This being the case leads me to the conclusion that you are simply trying to be smart or do not understand the regs book or the Installation methods being employed. The idea of this forum, from my understanding, is to help others get over problems they have encountered, misleading them with gumpf about installation method terminology is not helpful, simply distractful and does not do you any justice as a poster.

I would be happy to discuss such terminaology in another thread should you wish to do so, but I think we should leave it out of this discussion.

 

[FlyingScotsman]

Thanks for all comments so far.

Distance from shower to CU will be a maximum of 15m, probably slightly less. Saw a reference to a "calculator" for these sort of things in this forum and pumped in 10.5kw, 15 meters and it suggested 10mm cable which is what I think you guys are implying. 6mm seems slightly on the small side from a current carrying perspective and 16mm seems way over the top.

My heart and head says 10mm so I'll probably go with my gut feeling - but hey 15 meters of 10mm is pretty expensive when you've got to buy it on rolls!!

Thanks

 

[ban-all-sheds]

As I am new to this forum I have no wish to get into an argument with you Ban-all-sheds, however the reference method you use is not applicable in a domestic setting and therefore not applicable to this discussion.

Clipped direct?

This being the case leads me to the conclusion that you are simply trying to be smart or do not understand the regs book or the Installation methods being employed.

Neither. OOI - what installation method did you assume for a rating of 42A?

 

[andy]

Thanks for all comments so far.

Distance from shower to CU will be a maximum of 15m, probably slightly less. Saw a reference to a "calculator" for these sort of things in this forum and pumped in 10.5kw, 15 meters and it suggested 10mm cable which is what I think you guys are implying. 6mm seems slightly on the small side from a current carrying perspective and 16mm seems way over the top.

My heart and head says 10mm so I'll probably go with my gut feeling - but hey 15 meters of 10mm is pretty expensive when you've got to buy it on rolls!!

Thanks

go with 10mm. you can get in in 1M lengths from a local electrical place. or 25M coil. also, if you out 10mm in then you wont have to change it in future if you upgrade the shower

 

[Sparky Jim]

Neither. OOI - what installation method did you assume for a rating of 42A?

I apologise, that is a typo on my part, it should be 32A maximum rating. The table used is the correct one for T&E and is Table 4D5A -> 70C thermoplastic (PVC) Insulated and sheathed flat cable with protective conductor (Copper Conductors)

 

[mapj1]

For those with older copies of the regs, that table is revised here
http://www.iee.org/Publish/WireRegs/2001_Amd_1.pdf
Essentially, if you put 6mm cable,in conduit, in insuation, in a wall, its rating falls to 32A, while if you have it where it can cool itslelf, then the higher ratings apply.
In any case for the higher powered showers 10mm is needed in most cases, and its probably easier to route tha cable outside thermal insulation rather than step up to 16mm !
-it may be a DIY forum, but we do try and get the advice as near right as possible, and that means at least as good as the contract sparks

When working the 10mm T and E, inside the shower box, beware that the tail doesn't wag the dog, take the time to cut it carefully to size, form it to approximate shape to get the lengths of the cores just right before final cutting and stripping, and make sure it enters the terminals in-line and unstrained. And make sure its all nice clean metal/metal contacts, and nice and tight. The currents involved are high enough to bring a badly made connection to meltdown.

 

[Scoby_Beasley]

You need 10mm2 pal.