Cut-out fuse shared by 2 properties

[elementps]

Hi All,

Been to look at a job, where customer wants to install 9.5kw shower. 3 Bed 2 storey flat.

Calculating the load on board at present with diversity comes out at 68.8A, if the shower was added calculations came to 94.6A.
Looking in the meter cupboard, the supply splits to 2 meters after the incoming fuse, supplying the flat opposite. Is this common practice (not something I have come accross before)?
So as I see, the 100A supply is divided between the 2 flats, how can you possibly determine load, with the unknown of what next door are using? Any ideas on how to continue?

 

[GT1]

Personally I would look again at the max load figure your using. It seems very high for the type of property.?
I know there's no diversity available on showers... However putting a practical / real world angle on it, it's unlikely that you will have 60 odd amps worth of demand happening, AND the shower operating on top of that..?

 

[elementps]

I came to this by largest mcb rating + 40% of all other mcbs. Would you suggest working out actual loads on all circuits?

 

[GT1]

There are many and various methods used for calculating max demand, including the one you used.
Personally I should go by the OSG figures for diversity.
The method you used is a bit of a blunt instrument in my opinion.
I think you will find that the "true" figure will much less in reality.

 

[malcolmsanford]

I always used a formula given to me from an old DNO engineer and that is add up the protection devices in use and multiply by 0.4

so if you had 32+32 +6+6 +40+16 = 136* 0.4 = 54amps

 

[Engineer54]

I always used a formula given to me from an old DNO engineer and that is add up the protection devices in use and multiply by 0.4

so if you had 32+32 +6+6 +40+16 = 136* 0.4 = 54amps

And you would normally still be lucky to see even that 54A!! Even if you did, it wouldn't be for long, ....minutes at most!! lol!!

But Malcolm's method is as good as it gets and is a commonly used assessment of max demand. On the other hand using diversity figures from BS7671 isn't a very good idea, it will always give you final figures that, come nowhere near reality... The only one that has any real meaning to it, is that covering cooker loads upto 15KW....

 

[elementps]

Thanks guys, I do agree with the opinions on diversity calcs, always come out at very high values.
Any ideas on the shared cut-out fuse??? Anyone had to deal with something similar before?

 

[londonlec]

Ive seen it a few timers. Metering technicians dont like it, and usually moan/blow the job out.

Not sure how you'd get it altered, by speaking to UKPN (in London) I suppose.