10mm cable for shower - Why?

[ban-all-sheds]

When is somebody going to step in and do something about this?

According to FWL, some RECs are starting to provide 125A supplies.

Given that an increasing number of dwellings have two bathrooms and potentially, therefore, two electric showers, how are normal domestic supplies going to cope? There is a very high chance that both showers could be running simultaneously, along with a kettle, a toaster the cooker and maybe even electrical heating on a winter's morning. Let's say around 160A.

I think 160A is a bit extreme, but a 25-30kW load is not beyond the realms of possibility.

Okay, so a 100A BS88 fuse will handle 200A for around 25 minutes, but is it a good idea to regularly overload your service fuse like that? And are all consumer units and fuseboards built to deal with that current draw?

No they are not - I'm not aware of any domestic units with >100A incomers, but there's nothing to stop you using more than 1 CU.

HOWEVER - even with that solution, is there not a problem with the rated breaking capacity of the MCBs and the PSSC with a 125A main fuse?

I'm with B-A-S here - somebody stop B & Q from selling electrical kit to DIY-ers, please - showers and downlighters a priority!!!

We'll just buy'em from electrical wholesalers then....

 

[ban-all-sheds]

I've just bought an electric shower (9.8KW@240V, 9.0KW@230V) and although I have used 10mm TWE, the installation instructions say that 6mm TWE is ok?

Good job you took no notice of the instructions, eh?

 

[Igorian]

Good job you took no notice of the instructions, eh?

Well, some of them anyway? .

 

[securespark]

Merlin Gerin sell a 125A isolator - guess it is incorporated into CU's etc...

 

[dingbat]

Thanks for the detailed analysis Ban, but the point of my post wasn't about solving the problem for higher domestic usage, rather about the increasing abuse to which existing supplies are subject. It's getting harder to fill in the Maximum Demand box on the installation certificate without crossed fingers or a re-think of the diversity rules. Suddenly everybody wants to up the loads on every circuit, but doesn't want to pay to do it safely - plus ca change, huh? 500W floodlights all over the place, those interminable downlighters, big showers, extra sockets for multiple TVs, breadmakers, quick-boil kettles, more downlighters, etc, etc... and they want it all done after they've put down the now obligatory laminate flooring - the stone cladding of the noughties.

 

[ban-all-sheds]

Sorry, dingbat - you're right - I re-read your post, and I see what you mean.

 

[Mr Mac]

Ok lads Glad I managed to read all the messages. I'm just about to fit a 9.5Kw one and was wondering 6 or 10mm.

Regards.

 

[plugwash]

Given that an increasing number of dwellings have two bathrooms and potentially, therefore, two electric showers, how are normal domestic supplies going to cope? There is a very high chance that both showers could be running simultaneously, along with a kettle, a toaster the cooker and maybe even electrical heating on a winter's morning. Let's say around 160A.

I think 160A is a bit extreme, but a 25-30kW load is not beyond the realms of possibility.
could someone tell us how long a 100A BS88 or BS1361 will hold for at 160A

my guess is it will be longer than both showers are on for at once.

also in many areas people will be unable to use both showers at once because of water pressure issues anyway.

 

[mapj1]

fuse curves herehttp://www.bussmann.co.uk/images/Complete cats/Low Voltage/BS88 Curves.pdf
for BS88.
Looking quickly I see that a 100 amp fuse will carry 160A for the best part of 15 -20 minutes and over 200A for 3 or 4 minutes
most house service fuses follow curves similar to these
http://www.bussmann.co.uk/images/Data Sheets/BS1361/LR85.pdf
Not vastly different p[erhaps 200A for 5 mins or so, 160A for 20 mins/half hour or so...
Also rememebr when looking at these curves there is a fair spread, in terms of time to blow, at the slow end of the curve, depending on ambient temperature and cooling provided by the mounting arrangements.