The terms, motor rated current, full load current and nominal current, are very likely to confuse electrical engineers. Even though these terms are quite similar, there are slightly different from each other. Here is the clear definition of each one of them.
Motor rated current
The current drawn by a motor at its full load, calculated using formula is known as the rated current. Motor windings are designed to carry the rated current during normal operations and slightly higher than it for shorter duration.
Motor full load current
The full load current of a motor is the current drawn by it while operating at full load and rated voltage. It is a measured value and can also be calculated using formulae. The full load current may vary upon the applied voltage. Also, the rated full load current (FLC) is the one specified by the manufacturer while tested at ideal conditions.
Nominal current is the same as the rated current. It is the current drawn by the motor while delivering rated mechanical output at its shaft.
The formulae for rated current, full load current and nominal current are the same:
For single-phase AC motors
For single-phase motors, when kW is known:
For single-phase motors, when HP is known:
For Three phase AC motors
For three phase motors, when kW is known:
For three phase motors, when HP is known:
- Voltage: The phase-to-phase voltage for a 3-phase supply.
- Rating: The power rating of the motor in kW.
- Power factor (cosΦ): The rated power factor of the motor.
- Efficiency (η): The efficiency of the motor.
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