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I am using an dual voltage electric motor of 1.5Hp and RPM of 1750.Dual voltage motor works on 110Vac and 230Vac but with single 60Hz frequency. There is no over load protection built-in on the motor, but we allow the motor to trip if it draws more amperes than required using an ABB over load protection device. How do we learn how much should be limiting Amps drawn by the motor?

For example: Motor running at 230Vac draws 9.5A and 110V draws 16A. If this is the case how do I set the limiting amp rate on an Over load protection. Is it some percentage of over all current drawn at that voltage?

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  • \$\begingroup\$ This is an electrical engineering question, so I'm voting to migrate. The answer will depend on manufacturer's data, you must contact them if you don't know.. Be very careful: often "dual voltage" means the field winding connexion has to be manually set before use: with three phase motors this is often the difference between a star/delta connexion (e.g. star connected for 415VAC, delta for 240VAC). One phase dual voltage have two field windings connected in series for the higher voltage, parallel for the half voltage so that the field winding current is same in both cases for a given load. \$\endgroup\$
    – WetSavannaAnimal aka Rod Vance
    Sep 4, 2015 at 7:36

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As a thumb rule, we need to follow as mentioned below.(I got this info from ABB).

IF Service factor is 1.15, then set 125% from FLA. If Service factor is 1.0, We can set 115% from FLA.

In my question above, a motor drawing 230Vac draws 9.5Amps at FLA and this motor has service factor of 1.15. Thus the limiting motor load should be 125% the FLA which is 11.8Amps

And a motor running 110Vac draws 16 Amps at FLA and this motor has service factor of 1.15. Thus the limiting motor load should be 125% the FLA which is 20Amps

Please shed some light if anyone has better way to find the values.

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