Kva question

[green-hornet]

I have been asked to provide information to get a supply upgrade from single phase to 3 phase.

I have worked out the maximum demand to be 77 amps after diversity.

Normal calculations for 3 phase working is 3 x 230v x amps (77) / 1000 this would give a kva of 53.

It just appears to be a bit high, given that normal 80 amp single phase can supply up to 18 kva and 3 phase 100 amp up to 70kva.

The building is over 4 floors, with all associated lighting and power requirements including compressor and air con so my 77 amp requirement looks realistic enough.

Each floor will have its own cu.

What do you guys think ?

 

[Lee321]

kva is a value where power factor is concidered.

VxAx1.73 / 1000 this gives basic kw

include PF for kva

 

[green-hornet]

I have done the calculation with squared root (1.73) , if I gave each phase 30 amp I would get

1.73 x 400 x 30 /1000 = 20.76 kva

This I feel would be a more realistic demand for the installation, even allowing for an extra 10% or more for future add ons.

I just wanted to be sure my calcs were ok before I flew in with unrealistic demands.

Small loads do not usually require any power factor because of the lack of inductive loading etc, but I may be wrong been ages since I did any of these calcs.

 

[Andy™]

shorter calulation is amps per phase x 0.692

 

[kme]

Concur