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Topic Title: Diversity calcs for electric showers
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Created On: 10 July 2013 08:49 AM
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 10 July 2013 08:49 AM
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BrucieBonus

Posts: 756
Joined: 20 February 2007

Hi everyone

Just wanted to check your views on this as the Regs would suggest it can't be done, but applying common sense.......

60A main fuse, 2 bed flat
customer wants 2 x 9.5kW showers installed

At 100% for each this would take me over, and not withstanding the other loads...

I realise that the showers could be in use at the same time, but really would this take out the main fuse????

Thanks for looking

BB
 10 July 2013 09:37 AM
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AJJewsbury

Posts: 11786
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but really would this take out the main fuse

Probably not, but it would stress it a bit more than it's designed for (and overheating cut-out fuses can get messy!)
433.1 has words about small overloads of long duration - while one adult-duration shower probably wouldn't count as long duration, a couple of teenager-duration showers might be pushing it.

Personally, I'd go for getting the supply uprated, failing that how about on of these - http://www.meteorelectrical.co...wer-prioity-units.html ?
- Andy.
 10 July 2013 09:38 AM
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Parsley

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I doubt it would ever blow the 60Amp cut out fuse out on overload only.

Worth looking at 523.1 and 433.1, maybe fit a changeover switch if the customer doesn't plan on using the showers at the same time.

Regards
 10 July 2013 09:43 AM
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daveparry1

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I think 19kW on a 60amp fuse might be a bit much! It does depend of course on how long the showers are on for and also what other loads are present eg cooker, hob etc. I suppose that as a shower is only on for a few minutes (unless they have teenage kids!) you'd probably get away with it but I wouldn't be happy doing it. Maybe you could get the fuse uprated to 80a by the DNO if the supply could support it?

Dave.
 10 July 2013 09:57 AM
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Parsley

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Originally posted by: AJJewsbury

but really would this take out the main fuse


Probably not, but it would stress it a bit more than it's designed for (and overheating cut-out fuses can get messy!)

433.1 has words about small overloads of long duration - while one adult-duration shower probably wouldn't count as long duration, a couple of teenager-duration showers might be pushing it.



Personally, I'd go for getting the supply uprated, failing that how about on of these - http://www.meteorelectrical.co...wer-prioity-units.html ?

- Andy.


That looks like a neat unit Andy

Regards
 10 July 2013 10:23 AM
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BrucieBonus

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hi folks

Many many thanks for the speedy and helpful replies!

I've never seem one of those changeover units - useful to know.

What I omitted to say is that the customer is doing up the property as a buy to let and putting in an extra shower room, so I think the intention is that both could be used at the same time to avoid the bathroom rush. In which case the changeover unit rather takes out the idea of having shower 2!

The flat is in an ex council block (9th floor) and with notoriously poor management so I think there is ZERO chance of getting any supply upgraded even if DNO could/would do it

Plan B beckons

cheers

BB
 10 July 2013 11:12 AM
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daveparry1

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What's plan B then Brucie, walk away?

Dave.
 10 July 2013 11:37 AM
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BrucieBonus

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That's Plan C - (the 9th floor isn't selling it to me.... but I'm a bit quiet at the mo!)

Plan B would be one shower or go mains
 10 July 2013 11:55 AM
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daveparry1

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That's the problem when we're going through a quiet period Brucie, we tend to take on jobs which we would otherwise refuse! If there's a good supply of hot water maybe a power-shower would be better for one of them and electric for the other one,

Dave.
 10 July 2013 12:35 PM
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OMS

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OK - when load is a issue, I would tend towards storage vessels and mains showers - as the quality is better and it's kinder on the electrical infrastructure.

But BTL in an ex corporation flat - I guess you won't have the space and client certainly won't like the price.

Changeover is never a good plan - it just ***** people off.

Right - you need to deal with about a 2 x 40A load, that probably is not fully concurrent and actually not that long lived.

Given that a 60A cut out fuse will almost never blow at 70A and must blow within an hour at 90A, you are right in short duration overload territory that BS 7671 warns us about.

Given also that to warm a system up to temperature with a design load usually needs about an hour and even the most enthusiastic showers don't last that long - lets say worst case is 20 mins @ 80A. For the next several hours at least, the load is negligible.

For me, that tells me I have a load, that with a bit of maths, could become a thermally equivalant load of 80A x say 0.7 (derived from 1.0-0.3) then as far as the cut out fuse is concerned it would have to endure the equivalent of 56A (ish) full time (ie it's less than In)

So, if you have a 100A Dist Bd, meter tails of at least 16mm2 and your new circuit sizes are shall we say 10.0mm2, then basically - crack on, if you've the appetite for it. If you won't do it, someone else will - and probably with a bit of justification based on my ramblings above.

Please don't take this as a universal rule, but two showers isn't usually the drama we convince ourselves it is.

Hope that helps - bon chance

Regards

OMS

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Failure is always an option
 10 July 2013 02:03 PM
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BrucieBonus

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thanks OMS - food for thought..TBH the routes for the cabling are a nightmare (concrete floors and ceilings) so I'd not be too upset if only one shower went in.
The crazy thing is, is that the plumber/builder seems to have installed a hot water tank (and wants me to run a supply for an immersion) but the existing boiler is a combi - just don't get this. The customer hasn't a clue - builder seems to be making all the decisions. Feel sorry for the customer really... the builder wants the second shower to go in a cupboard off the kitchen....nice
 10 July 2013 02:23 PM
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OMS

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OK - if you want the work and love minitrunking then it's do-able -

Unless you are being paid for technical advice, let the plumber get on with it - his drama not yours.

I know what you mean about the customer - but there you go, no-one held a gun to thier head.

Regards

OMS

-------------------------
Failure is always an option
 10 July 2013 02:35 PM
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daveparry1

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Builders should do just that, "build", not planning, decision making or anything of a technical nature!

Dave.
 10 July 2013 03:56 PM
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BrucieBonus

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hear hear - I just need to forget all about this and think of the money
 10 July 2013 04:21 PM
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OMS

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Originally posted by: BrucieBonus

hear hear - I just need to forget all about this and think of the money


Well you can try, I guess - doesn't always work of course - terrible thing a conscience on occassion

Regards

OMS

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Failure is always an option
 10 July 2013 07:14 PM
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MrOther

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Originally posted by: OMS

For me, that tells me I have a load, that with a bit of maths, could become a thermally equivalant load of 80A x say 0.7 (derived from 1.0-0.3) then as far as the cut out fuse is concerned it would have to endure the equivalent of 56A (ish) full time (ie it's less than In)


OMS


Currently digesting this at breaks:

http://www.amazon.co.uk/Electr...15504/ref=pd_sim_b_17

To better educate myself, and see or at least think and conceive whether their is possibility away from the tools (bad knees) and I remember their was a large table of suggested diversity factors for suggested circuits. My question OMS is was your figure of 0.7 a real diversity factor, a mere example for your scenario, or based on experience?

Cheers.
 10 July 2013 08:43 PM
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peteTLM

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Hold on did i hear that there is a combi boiler there? Why on earth would you want 2 rubbish electric showers then?

Best solution would to have a megafloe, heated by the boiler or electric.

Its obvious that the plumber hasnt got a clue- electric showers- hot water tank and combi boiler??????

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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 10 July 2013 10:31 PM
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AJJewsbury

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9th floor flat - how tall is the block? what's the betting the water pressure is rubbish?
- Andy.
 10 July 2013 10:56 PM
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UKPN

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"but really, would this take out the main fuse????"


Regards.

has your consultant really got the experience?
 10 July 2013 11:47 PM
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sparkingchip

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16 litres of water per minute @ 1 Bar pressure with a Eco Shower being 8 litres per shower, which is more like 10 litres with other models.

You need to make up a piece of pipe with a pressure gauge mounted onto it with a tee and a tap on the end so you can attach it to a tap in the flat which is cold mains fed, usually the kitchen sink then use this to set up a flow of 16 litres per minute measured using a flow cup and check the pressure.

This way you get the running pressure rather than the static pressure. Then close the flow off and check the static pressure which should not exceed 10 bar.

If they can't get the water then the power supply isn't a issue is it?

Andy
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