Single phase and Three phase useful formula's

Rules Of Thumb (Approximation)
At 1800 rpm, a motor develops a 3 lb.ft. per hp

At 1200 rpm, a motor develops a 4.5 lb.ft. per hp

At 575 volts, a 3-phase motor draws 1 amp per hp

At 460 volts, a 3-phase motor draws 1.25 amp per hp

At 230 volts a 3-phase motor draws 2.5 amp per hp

At 230 volts, a single-phase motor draws 5 amp per hp

At 115 volts, a single-phase motor draws 10 amp per hp


Mechanical Formulas
Torque in lb.ft. =

HP x 5250

rpm







HP =
Torque x rpm

5250




rpm =
120 x Frequency

No. of Poles


Temperature Conversion

Deg C = (Deg F - 32) x 5/9
Deg F = (Deg C x 9/5) + 32 

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