Block of flats. Max Demand

[bartkusal]

Wonder if I can get some guidance, on max demand in block of flats. It always was hard for me as it always comes to massive demands, and I red here that it all comes with years of experience and that it is like an art. This is first bigger project I am taking on. So please don’t shoot.

I need to determine the max demand for the job, so the correct supply can be brought in.
Basically it is an old mansion being converted to a block of 11 flats.

Each flat will have: 2 lighting, 2 ring, 1 shower 8.5kW (37A), 1 cooker 4.5 kW (19.6A).

Option 1: Going by OSG diversity: 4A lights+4A lights+32A ring+8A ring+37A shower+16A cooker=101A (crazy)

Option 2: Going by 0.4 factor diversity: (6+6+32+32+37+19.6) x 0.4 =53A (more like it)

For the whole house:
Can I treat flats as circuits in this instance and apply 0.4 factor again? Then:

Option 1: ((101A x 11)+ 20A landlords board) x 0.4 =452A (3Ph), Supply current per phase 452/3=150A. So I need then 103.5kW 3ph+N supply.

Option 2: ((53A x11) +20A landlord board) x 0.4 = 241A (3ph). Supply current per phase 241/3=80A. So I need then 55.2kW 3ph+N supply.
I find myself thinking to come up with Option 3, :banghead:: (option 1+ option2) /2. =80kw 3ph + N supply.

So what you think? Am I somewhere near with my thinking? Obviously if I can’t work it out I will go with safest but unfortunately most expensive option 1, it just seems it will be rather large supply cable 50 mm2 or maybe higher, it is what it is I suppose. Not sure about ratings on supply cables, just had a look in regs book, 50mm2=135A and 70mm2=167A, SWA XLPE reference D, obviously its different cable.

After and if I will get this confirmed by more experienced, I then will share with my calcs and plans of action for the customer’s installation.

Thanks in advance for your help and guidance.

Al

 

[driverman]

Re flats: Generally now all meters to each flat have to be on the ground floor altogether in a community room whereby each tenant/ owner has 24 hour access. The DNO would have to install a suitable sized mains cable (possibly 95cne) into a Ryefield box to cater for 11 flats plus "Landlords supply" for corridor lighting and fire alarm. From the Ryfield box a separate cable to a 60/80amp cut out (header) fuse is supplied for each flat. The supplier will the connect a separate meter to each and every flat. A suitable sized switch fuse is then fitted by the electrician, running a separate sub main to each flat consumer unit. To accommodate all the DNO's equipment , meters, switch fuses etc a large area is required. Basically all the cut -out fuses and meters are next to each other along with the switch fuses.