Sizing a transformer

[ericstac]

I need some help on this project where I have a tenant who is taking on a second space next to them which currently has its own meter. The city is requiring them to only have one meter for the entire build out now. Currently one unit has a 480/277 and the other has a 208/120 225amp.. The plan is to use the 480 as the main and feed the other panel.

here are my calcuations:

VA = [(225 A)x(208 V)x3^.5]/1.25 = 64,848 VA

Is this correct?

so i would need a 480/277 - 208/120 65 KVA transformer?

 

[Ingenieur]

Why derate by the 1.25?
are you planning on 80% on the 225 panel?
your calcs are correct
80kva load at 80% capacity 65 kva
whatever the next larger standard size, perhaps a 75

you probably want a 480 delta : 120/208 wye
derived neutral on the secondary

 

[ericstac]

I just used a calculation I found here on the forums.

So if I go with a 75kva we are talking upwards of $2500.00 for this. Does that sound about right? :blink:

 

[Ingenieur]

I just used a calculation I found here on the forums.

So if I go with a 75kva we are talking upwards of $2500.00 for this. Does that sound about right? :blink:

not sure about pricing, guessing 7500-8500
a General Purpose Square D/Schneider with Al windings should be fine

 

[Ingenieur]

Verify that the 480 mdp can take the additional 75 kva
90 A off the 480

might be cheaper to have the utility provide the xfmr and put in a new service