maximum demand kva 3 phase

[daveb1]

looking to get a bit of help got a job that currently has 8 flats and a landlord supply and a big office on the ground and basement

After using the OSG for diversity have come up with the following

118A per flat (no gas)
127A for landlord (lift etc)
180A for office (air con)

118x8=944+127+180=1251AMPS this seems way to much i know! but would rather cover myself so when the office are giving these to the supply company they are asking for kva?

At the moment they have a 200A 3 phase supply

The developers are looking to change the office into 3 more flats so 3X118=354amps more

so with the office gone we are looking at a total of 1425Amps (sounds like its getting confusing)

so my question is how can i get a kva value for the supply company? with 1425A 3 phase

Any help would be appreciated Thanks Dave

 

[Plonker 3]

Can you give a breakdown of the cicuits in each of the 3 different areas?

 

[Darkwood]

Considering most large houses happily run on 60/80/100 supply I'll be surprised if yo get a flat demanding 118amps, the Landlords supply sounds excessive too Im sure your miscalculating here.... by your reckoning you'll need a supply that would be adequate for most large factories !!!

 

[daveb1]

flats (off the top of my head, been a few years since been inside no access to flats )

kitchen ring
main ring
electric boiler
cooker
hob
light
light

office (no access)
over two floors, i know there is
electric shower
kitchen
air con
lights?
sockets?


landlords i could see
3p lift 40A
small lift dis board 32A
2x ring circuits
3xligts
fire fan control system

Thanks Dave

 

[dan86]

as per darkwood- me thinks there is a duff calculation somewhere. 118a for a flat sounds hugely escessive.

 

[daveb1]

i know its seems mental but it the way i was told how to do it by 2394/5 tutor
doing it this way the average house comes out at 145 ish, an its funny to think most are fused at 60/80

 

[Darkwood]

Either your tutor is crap or you haven't fully understood it.

Still lacking a lot of info to make comments ... is heating off peak to flats?
As you don't even have access to the offices how can you make a reliable calculation?

You need to do some on-site investigation - im afraid guess work because of limited access isn't an excuse - sort access out get a better idea of the installs

 

[wozz]

your tutor told you to use that as that the subject he is teaching. The stuff in the OSG isnt really any use in doing the diversity in a install such as yours.

 

[daveb1]

Yes you are right about access will get in to see all the distribution boards for myself
No there is no off peak heating

Ok i could have miss understood the point and the tutor could also be crap but we were working all this out from the on site guide, i know these are not real life in book. just want to cover myself thats all.

 

[daveb1]

Oh yes when i have done my homework got some proper info could anyone tell me the formula for kva? and do i calculate per phase or an overall value
Thanks Dave

 

[Darkwood]

Ball park figure 1P KVA is ( KVA x 4) so 25KVA will be 100amp
3P KVA is ( KVA / 0.73) so 73KVA will be 100amp per phase.

Transpose as needed... again a quick method for a ball park figure!

 

[GMES]

Dave as Darkwood says that sounds way to high for what you are proposing , I mainly do industrial/commercial and most factories don't have anything like 1200 amps coming in to them. time to do a full and precise spec on the job / site. plus it could save the customer a hell of a lot of money.

 

[i=p/u]

I done a 2 bed flat today and it worked out at , highest breaker + 40% of rest = 92A but don't forget the heating was on 16A breaker , 2 ring circuits, a plug top cooker on 32A

 

[i=p/u]

Where's .73 come from for 3ph ?

and for single phase isit 100A x230v =23kva

 

[Darkwood]

Where's .73 come from for 3ph ?

and for single phase isit 100A x230v =23kva

I said quick ballpark method.... so does 0.73 work or not to give Amps per phase in 3ph