Transformer sizing

[g-and-h_electric]

Hey guys, old customer of mine is adding more computer build space in his warehouse ( He is in the IT business). I need to add a panel and transformer 480 delta 120/208Y, and a panel. Approximate calculated load at this time is about 220 Amps total. (6 build benches at about 30 amp each... this would be 2 20 Amp circuits per bench plus lighting load, and a 40 Amp feed to another modular office for the shipping manager)

Anyway, We have onsite a 150kVA transformer which is not in use. If the primary has an OCP of 100Amp, and the panel has OCP of 200 Amp, does anyone see an issue with using it? I know it is way overkill, but is already owned by the customer, and there is a 100 Amp disconnect in the main gear with feeders heading that are not in use heading very close to where all of this is going. There is also a 45 kVA onsite likewise, it is not in use, just sitting on a pallet looking for a something to do. I am thinking the 45 is a little light .

Any thoughts????


Howard

 

[electrofelon]

I'm thinking the load will be drastically less than your numbers. What happens in these build benches?

 

[g-and-h_electric]

Th customer is installing software and all on laptops and desktop computers. There will be approximately 10 to a bench ( we know there may be more) I used 2.5 amp per computer as a guideline . Also I need to feed the "shipping office" from here.... that will have 1 gen purp recept circuit, 1 lighting, 1 A/c heat circuit, and 1 dedicated for a shrink wrap machine ( 16 A load max, prolly 5 min use at a time )

As this is an old long time customer I try to plan for the future as things change there occasionally.


howard

 

[augie47]

As much as I lean towards oversizing for customers who have growth in your case I would go with the 45kva. I would be concerned placing the 150 on a 100 amp breaker even if it is under utilized. Play with the numbers and you will see with a 3 phase system the 45kva seemingly is adequate.
(Based on 2.5 per computer X 10 per bench X 6 benches + your shipping load I see about 30kva load and that's with no diversity)

 

[ptonsparky]

Getting the 150 KVA to start up without tripping the 100 Amp breaker at inrush is the biggest issue. Once its On you should be good to go, until it trips and won't reset.

 

[electrofelon]

Yeah there are two problems with the 150, even with it being free. One is no load losses, and this would be especially true if this is an older pre DOE2016 unit. The other is getting a large enough OCPD on the primary side to start it. Unless you have a large distribution board with a big breaker, that is tough to do without getting creative.