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The overloads are determined using 125% of the FLA, 7A x 1.25 = 8.75A. The maximum allowable size for the overloads is 9.8A. The overloads can be sized at 140% of the FLA if the overloads trip at rated load or will not allow the motor to start, 7A x 1.4 = 9.8A.

What should the overload setting of a motor be?

Normally setting for overload is 5% until 10 % more than FLA. But it is depend on operation and functional of motor. For more detail setting,please refer manual guide of motor from manufacture. We also can setting overload relay value depend on value of service factor motor.

How do you calculate motor load percentage?

Por = Nameplate rated horsepower Load = Output power as a % of rated power Pi = Three-phase power in kW η = 0.7457 x hp x Load Pi Page 8 8 By definition, a motor of a given rated horsepower is expected to deliver that quantity of power in a mechanical form at the motor shaft.

Do all motors need overload protection?

EVERY motor needs overload protection of some type. Some small motors are impedance protected by design. Some motors can be overload protected by breakers or fuses. Some motor have internal temp probes that shut down the motor starter.

Unplug the start relay from the compressor and give it a shake. If you can hear rattling on the inside of the start relay, then the part is bad and will have to be replaced.

What is the efficiency formula?

Efficiency is often measured as the ratio of useful output to total input, which can be expressed with the mathematical formula r=P/C, where P is the amount of useful output (“product”) produced per the amount C (“cost”) of resources consumed.

How is motor rating calculated?

Multiply the motor voltage by the full-load current. The result is in watts. Divide watts by 1,000 to give kilowatts. For example, 230 volts x 20 amps = 4,600 watts; 4,600 watts divided by 1000 = 4.6 kilowatts.

How do you overload a motor?

Divide by the rated full load current from the motor nameplate. This will be the load factor for the motor. If the motor current is 22A and the rated full load current is 20A, then the load factor is 22/20 = 1.1. This means the motor is overloaded by 10%.

What is used to protect a motor from overload?

Overload relays protect the motor, motor branch circuit, and motor branch circuit components from excessive heat from the overload condition. Overload relays are part of the motor starter (assembly of contactor plus overload relay). They protect the motor by monitoring the current flowing in the circuit. 