Step up Transformer

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Mark W.

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O'hare Airport
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Union Electrician
It's been a while for me to size up a transformer, I need to size up a 208v 3ph primary to a 480v 3ph secondary step up transformer. The only load it is feeding is a continuous duty air handling unit at 480v 3 phase max 15a. How would I go about doing this, what size transformer will I need?
 
The devil is in the details. Is the 15 amp Max OCP or the motor FLA ?
In its simplistic form you have a 12 kva load (15 x 480 x 1.732) and the next "standard" size 3 phase transformer would be a 15kva but with a motor load the motor details would be important.
 
Welcome to the forum.

Use 3ph math to convert 15a at 480v to Kw. (Hint: ~12.5)

Decide how much overhead you need for starting, PF, etc.

Select a 208D/480Y (for simple grounding) at 15 to 22.5 Kw.
 
LarryFine said:
Welcome to the forum.

Use 3ph math to convert 15a at 480v to Kw. (Hint: ~12.5)

Decide how much overhead you need for starting, PF, etc.

Select a 208D/480Y (for simple grounding) at 15 to 22.5 Kw.
Click to expand...
LarryFine said:
Welcome to the forum.

Use 3ph math to convert 15a at 480v to Kw. (Hint: ~12.5)

Decide how much overhead you need for starting, PF, etc.

Select a 208D/480Y (for simple grounding) at 15 to 22.5 Kw.
Click to expand...
The only info I have is on the nameplate of the unit
Rated Voltage 480v 3Ph
Min. Circ amps 6.9amps
Max overcurrent protection 15amps

Blower motor 5.5 Fla 3.0 H.p.
Factory RPM 1112
Max Allowable Rpm 1500

I don't have any other info like power factor off the nameplate of the motor
 
Appears the motor is the only load.
Have you checked to see if it's dual voltage or for a motor rated 240.
Be a lot less expensive than the transformer arrangement.
 
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