This made my eyebrows go up!

[New Venture!]

Request in the form of "would this be possible" in a large family home that's being refurbished.

1) Two shower rooms, each fitted with a 10.8 kW electric unit
2) 7.2 kW induction hob.
3) Two double ovens, each rated at 4.6 Kw.
4) In kitchen. Washing machine, tumble dryer, dishwasher, kettle, coffee maker, toaster, food processor, juicer, waffle maker, bread maker, freezer, American style fridge freezer/larder. 
5) Three socket rings for house, each rated at 7.2 kW.
6) Three lighting circuits, each rated 1.5kW
7) Workshop feed, 10.8kW.

The socket rings are very unlikely to be loaded anywhere near max, same with lighting circuits. But if two daughters are having showers while a large dinner is being prepared, with dad playing in the workshop...........

 

[ProDave]

We have two 8.5KW showers often in use at the same time with no problem (I have seen 90A load before now)

As most people shower late evening or first thing in the morning, it's rare to be coking at the same time.
 

 

[New Venture!]

I agree Dave, but it brought home just how much juice a house (in theory) could pull! 

 

[rapparee]

Well you could wire it through a contactor that would only allow one shower on at a time.

 

[Lurch]

Coulda woulda shoulda.

I've fitted 3 8.5kW showers in a large family home with electric cooking and power to outbuildings and barns etc. Never been a problem. Think it might have been a reduced supply (60A) too. On paper it is a bad idea. Realistically it will probably be fine.

 

[rapparee]

Coulda woulda shoulda.

It's standard practice round here.

 

[Evans Electric]

Yes if you do the maths and read the Regs and the OSGs  and all the rest of it , it won't work  but  just do it ...it'll be fine  .   

If you look at the service fuse characteristics you'll see.  

 

[Rob_the_rich]

It's standard practice round here.

Do you get one person turning on the shower, then using wc, then cleaning teeth, then a quick power nap etc., then showering, just to be the first?

 

[New Venture!]

I'm heading out to have a look at the place next week. These figures are from (I think) the architect. Pretty sure I can shave them down a bit, maybe even convince them to go for slightly less powerful showers. I do want to see a 100 amp supply though! 

 

[rapparee]

Yes if you do the maths and read the Regs and the OSGs  and all the rest of it , it won't work  but  just do it ...it'll be fine  .   

If you look at the service fuse characteristics you'll see.  

I meant standard practice to fit a contactor, not throw in three electric showers.

Do you get one person turning on the shower, then using wc, then cleaning teeth, then a quick power nap etc., then showering, just to be the first?

I wouldn't know, i hate electric showers i wouldnt have one in my house if i was living there long term.

 

[Rob_the_rich]

I wouldn't know, i hate electric showers i wouldnt have one in my house if i was living there long term.

Makes sense to keep one if already installed, in case the combi packs up.

 

[Lurch]

maybe even convince them to go for slightly less powerful showers.

Electric showers are rubbish. I wouldn't go below 9.5kW, so from 10.8kW it's hardly worth mentioning. What I would do instead if there was no other option is fit an electric boiler and pressurised cylinder instead. What is doing the heating in the rest of the house? You haven't mentioned it in your spec so I assume it must be a wet system of some kind? You architect might want cluing up a bit on better ways of providing 3 showers to a property.

Makes sense to keep one if already installed, in case the combi packs up.

People say this, but in reality an electric shower is likely to be as reliable as a combi boiler for the most part so law of averages and all that, might as well stick to one or the other.

 

[rapparee]

Makes sense to keep one if already installed, in case the combi packs up.

To be honest every electric shower i've ever been in has been a disaster. It's either freezing or scalding and you could pi$$ harder. It's probably down to what you're used to, they're just not for me.

 

[New Venture!]

I only know what was e-mailed across after a phone call asking if I would do the electrics. No idea what hot water system they're going for, or any other details. If it's a combi, one standard thermostatic shower along with one electric could be an option. Mains pressure hot water good suggestion too.

I'll make some suggestions and hopefully come to something everyone is happy with. 

Oh, one extra......these are the showers.....

http://www.screwfix.com/p/mira-sport-max-with-airboost-manual-electric-shower-white-10-8kw/87467

 

[Jwaterworth90]

looking and reading this please correct me if i am wrong as i am learning still, 

however the maximum amp for the household if everything were to be turned on and running ( obviously unlikely ) would be 325 amp (from above figures )  ?

however usually a house has either a 80 amp main fuse or a 100 amp mains fuse it wouldn't take a lot for this to blow the main fuse 

say two people are showering at the same time in a 10.8kw shower 10800 x 2 = 21600 divided by 240 = 90 amp

plus say mother or the father is also cooking the tea or doing some DIY jobs in the workshop 10.8 plus 4.6kw = 15400 divided by 240 = 64 amp 

bringing a total of 154 amp ?

am i correct in saying this is possible to achieve these Amps or is it unlikely that appliances will be running at their full potential i.e an electric appliance is probably rare that all four rings are being used and the grill and oven ?

 

[Bruspark]

Jwaterworth90

Google Diversity Factors for domestic electrical supplies.  

Google 80 and 100 A BS88 and BS1361 fuse blowing curves

Rarely do the two meet in the middle

 

[Rob_the_rich]

bringing a total of 154 amp

From the table for an 80A BS1361 fuse in the big red book, it would carry 154A for about 2000 seconds, about half an hour. Hopefully one of the showerers would be finished by then, or the water on the rings would be boiling and turned down to simmer. A 100A fuse would carry it for about 7000 seconds, about 2 hours.

 

[Rob_the_rich]

say two people are showering at the same time in a 10.8kw shower

It appears to be the same shower :worthless:

 

[Bruspark]

It appears to be the same shower :worthless:

To be fair I find showers with two often take longer :slap

 

[Jwaterworth90]

thank-you for reply, its a interesting topic.

i went to a job the other week where a customers house main fuse had blown ( 60amp ) there was a none RCD board in at the time but the MCB did not trip.

he said the hob rings went bright red then everything just went bang. is this due to the cable over exceeding its rating causing the main fuse to blow ?