Transformer sizing for single phase motor

[Alan K]

.5 HP pump, 230Volts, Single phase, Full load Amps=8.5, Locked Roter Amps= 30.1A, NEMA Start code "R"

Primary voltage is 480V. What size single phase transformer required for this pump?

 

[Jraef]

.5 HP pump, 230Volts, Single phase, Full load Amps=8.5, Locked Roter Amps= 30.1A, NEMA Start code "R"

Primary voltage is 480V. What size single phase transformer required for this pump?

Gross rule of thumb: minimum transformer kVA = 3X the motor HP value if there is nothing else on the circuit and starting across-the-line. So your motor is 1/2HP, use a 1.5kVA transformer minimum.

 

[gar]

130525-0906 EDT

Alan K:

0.5 HP 230 V and full load = 8.5 A looks wrong. VA = 1955. 0.5 HP output = 746/2 = 373 W. If you assume 85% efficiency and 0.8 PF, then VA = 550. A 1/2 Hp Sears motor of mine at 230 is labeled 4.3 A, or 989 VA. Are you reading the the 115 V full load amperes?

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