9.5 kw shower on 6mm ?

[wade88]

Oooo brilliant i've just sat down for my lunch i definitely think ill be staying to watch this little firework display unfold. How exciting, yet ANOTHER feeble display of bickery.

I would have thought it was a fairly straight forward answer however? Stick with what the regs recommend - and you can do no wrong. Is that not the basis on which we as electricians design and guide our circuits around to adhere to safe and proper practice? Or have i missed something where personal opinion counts for more than the governing body by which we all follow. But i don't know.... that's just my opinion. Am i allowed to say that or do i have to note that as a departure :stuart:

 

[Guitarist]

I am still amazed at how many people think that British electric showers are a variable load. 8.5kw is 8.5kw, regardless of anything (except variations in supply voltage ofc). If you select the "economy mode", which tbh nobody ever does, then it will be a lower fixed load, but still fixed....

 

[Sherwoods]

The cable size must be suitable for the load, no matter what overcurrent protection is provided. No reference method has been mentioned, but if it is "A" then 6mm is rated at 32A, method 100 rated at 34A, and 101 would be only 27A.
A 9.5 kW shower would draw 41.3A.
I have seen a few cases where the shower isolator is starting to disintegrate due to the high load and a situation where the contact resistance continues to increase. This, along with the inadequate cable current capacity is a fire risk. The conclusion must be that the shower in the quoted case must be rewired or the shower replaced with the correct rating.
The overcurrent protection should match the load but not exceed the cable current rating.

 

[Guitarist]

Just to add my tuppence worth,
I have seen many, many 8kw and above showers wired in 2.5mm flex from the isolator to the actual shower unit in my time testing, none of which showed any signs of damage, poor terminals and terminations cause many more,
I think in an ideal world there should be a 'domestic shower diversity' added to the regs, it irritates be to give a code 6mm supplying showers in houses, in fact I often give it a code 3 rather then 2 if there is no heat damage.

I hope you are not condoning 8kw showers being fed with 2.5mm cable.

 

[sedgy34]

i cant be bothered to read through them 10 pages but has anyone thought what the manufacturer wants to keep the warranty in place normally correct fuse rating to the bs7671 and an rcd in place "just my 2penny worth"

 

[Guitarist]

i cant be bothered to read through them 10 pages but has anyone thought what the manufacturer wants to keep the warranty in place normally correct fuse rating to the bs7671 and an rcd in place "just my 2penny worth"

A lot of shower manufacturers state a minimum cable and MCB size. All this has been said so many times before, yet still people are arguing about whether to work from "experience" or adhere to the regs! We know that everything has a safety margin built-in, but that's exactly what it's for, safety.
I think that the phrase "well, the last house didn't burn down", is not going to be much use if it all goes belly-up.

 

[telectrix]

when we look at it, so a 6mm cable is installed method C. it is perfect for the situation at time of installation. OK, so in the future a muppet might cover it in itchy snot, thus derating it's CCC. but, in the future rats/mice may infest the loft, so do we install SWA or cable in steel conduit? client may, in the future, get a plumber to install a 15kW shower, do we allow for that?

 

[Engineer54]

I'm just wondering how many of these manufactures stated KW ratings are actually achieved in the real world??

 

[telectrix]

exactly.

 

[Dave 85]

Youre correct of course but your example is out of context to the original post.
The issue that was debated at the start is regarding utilizing an existing cable so as to reduce cost / inconvienience to the customer in having a bigger cable installed.
Its a judgement call that each person will assess differently , but in my experience a 9.5kw shower will run off 6mm with absolutley no problems for years , regardless of any calcs you want to throw at it.

And here we have the difference between a proper sparky and a regs jockey.