Question

What is the minimum current rating of the motor disconnecting means for a 40-horsepower, 208-volt, 3-phase squirrel-cage motor?

Answer 1

The minimum current rating of the motor disconnecting means is 165 Amperes.

Step-by-step explanation:

First convert the given power into units of watt. Since,

1 horsepower = 746 watts

Therefore,

40 horsepower = 40 x 746 watts

40 horsepower = 29840 watts

Since, we know that:

Power = Full Load Current (FLC) x Voltage

FLC = Power/Voltage

FLC = 29840 watts/208 volts

FLC = 143.46 Amperes

Now, the current for disconnecting means is at least 115% of the FLC, for the motors rated at 600 Volts or less.

Current for Disconnecting Means = (1.15)(143.46 A)

Current for Disconnecting Means = 165 Amperes