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#### CPorter

##### Member

Oncor tells me two buildings we are to lease are fed by three single phase 500KVA transformers rigged to supply 208vac three phase. They say this is good for 2000 amps.

Lighting loads are 3.5va/sqft = 50,000*3=150KVA by 200.12 and demand is 100% by 220.42

Receptacle loads in 200.14(I) & (K) amount to 1VA per sqft with demand (220.44) at 100% for the first 10KVA and 50% after. At 50,000 sqft thats 10kva + 20kva =30KVA.

Gathered the name plate data from the AC units I have 1092.3 amps total from the 3 phase units and 383 amps total from single phase units. Don't know what demand factor to use but experience from repairing ac unit tells me they run pretty close to FLA during the summer 100+ degree days.

We want to run a data center on this and right now it draws about 320 amps per phase.

The lighting load appears to run 420 amps per phase.
The AC loads are about 280 amps per phase for the 208V single phase stuff and 1092 for the three phase stuff.

Max calculated load on any one phase is about 1875 amps without the data center and 2225 amps with it.

2225*208*1.73/1000 = 800KVA for the transformer minimum.

#### bob

##### Senior Member

Oncor tells me two buildings we are to lease are fed by three single phase 500KVA transformers rigged to supply 208vac three phase. They say this is good for 2000 amps.

Lighting loads are 3.5va/sqft = 50,000*3=150KVA by 200.12 and demand is 100% by 220.42

Receptacle loads in 200.14(I) & (K) amount to 1VA per sqft with demand (220.44) at 100% for the first 10KVA and 50% after. At 50,000 sqft thats 10kva + 20kva =30KVA.

Gathered the name plate data from the AC units I have 1092.3 amps total from the 3 phase units and 383 amps total from single phase units. Don't know what demand factor to use but experience from repairing ac unit tells me they run pretty close to FLA during the summer 100+ degree days.
Assuming your calculations are corect I get 1815 amps.

We want to run a data center on this and right now it draws about 320 amps per phase.

The lighting load appears to run 420 amps per phase.
The AC loads are about 280 amps per phase for the 208V single phase stuff and 1092 for the three phase stuff.
You say the data center load is 320 amps but then you give the lighting load as 420 amps + rec load as 83 amps + A/C 280 amps + A/C 1092 amps for a total of 2287 amps.
Max calculated load on any one phase is about 1875 amps without the data center and 2225 amps with it.

2225*208*1.73/1000 = 800KVA for the transformer minimum.
So new load is 1815 amps + data ctr 2287 amps = 4102 amps.
The 3 500 kva transformers are good for 4168 amps. Please clear this up.

#### CPorter

##### Member

Bob,
The new load is 1815+350=2200 amps. The transformers are good for 4167 amps as 120 volt single phase but these are set up for 208y120. A three phase transformer rated at 500 kva is only rated for (500*1000)/(208*1.73)=1390amps.

#### kwired

##### Electron manager
Bob,
The new load is 1815+350=2200 amps. The transformers are good for 4167 amps as 120 volt single phase but these are set up for 208y120. A three phase transformer rated at 500 kva is only rated for (500*1000)/(208*1.73)=1390amps.
Correct for a single - three phase 500kva transformer. You said you have 3 - 500kva single phase transformers connected to form a wye system. You essentially have a 1500 kva transformer which is 4168 amps @ 208 volt 3 phase.

#### bob

##### Senior Member
Bob,
The new load is 1815+350=2200 amps. The transformers are good for 4167 amps as 120 volt single phase but these are set up for 208y120. A three phase transformer rated at 500 kva is only rated for (500*1000)/(208*1.73)=1390amps.
CP
you have 3 500 kva transformers that equal 1500 kva/(0.208 x 1.73) = 4168 amps.

#### CPorter

##### Member
Wasn't sure how that worked but now I'm confused as to why Oncor said it's good to 2000 amps.

#### augie47

##### Moderator
Staff member
POCOs use their own diversity factor and their own overload factors.
Conjecture on my part, but I assume they are saying if you show a 2000 amp service they would supply a 500 kva transformer.
Most often they want to look at the actual loads as you presented them and then determine what transformer they will use.

#### hbendillo

##### Senior Member
Are these pole mount type transformers? Rarely see them that size around here. Get over about 500 KVA total and you usually get a three-phase pad mounted transformer.

#### CPorter

##### Member
It's a pad mount to a commerical building. After a bit of back and forth conversation with Oncor it has been agreed the a 500KVA is too small and they are going to install a 750kva. Their diversity factors dropped the calculated load to 694 KVA.

#### kwired

##### Electron manager

Oncor tells me two buildings we are to lease are fed by three single phase 500KVA transformers rigged to supply 208vac three phase. They say this is good for 2000 amps.

Lighting loads are 3.5va/sqft = 50,000*3=150KVA by 200.12 and demand is 100% by 220.42

Receptacle loads in 200.14(I) & (K) amount to 1VA per sqft with demand (220.44) at 100% for the first 10KVA and 50% after. At 50,000 sqft thats 10kva + 20kva =30KVA.

Gathered the name plate data from the AC units I have 1092.3 amps total from the 3 phase units and 383 amps total from single phase units. Don't know what demand factor to use but experience from repairing ac unit tells me they run pretty close to FLA during the summer 100+ degree days.

We want to run a data center on this and right now it draws about 320 amps per phase.

The lighting load appears to run 420 amps per phase.