Question

The disconnecting means for a motor circuit rated 480 volts nominal will have an ampere rating of a minimum of what percent of the full load current rating of the motor?

1. 100%
2. 115%
3. 125%
4. 130%

Answer 1

4. 130%. The disconnecting means for a motor circuit rated 480 volts nominal should have an ampere rating of a minimum of 125% of the full load current rating of the motor. The minimum ampere rating for the disconnecting means should be 130% of the full load current rating.

Step-by-step explanation:

The disconnecting means for a motor circuit rated 480 volts nominal should have an ampere rating of a minimum of 125% of the full load current rating of the motor.

To calculate the full load current rating of the motor, we need the motor operating voltage and power rating. Once we have this information, we can use the formula:

Full load current rating = Power rating (kW) / Voltage rating (kV)

Let's say the motor has a power rating of 50 kW and an operating voltage of 480 V:

Full load current rating = 50 / 0.48 = 104.17 A

125% of 104.17 A is approximately 130 A. Therefore, the minimum ampere rating for the disconnecting means should be 130% of the full load current rating, which is option 4.