Motors: Theory and Application

A polyphase synchronous motor has three stator windings that are

120 apart

The power factor of an induction motor at no-load conditions can be as low as

15%

The synchronous speed at which a four-pole, 60Hz induction motor operates is

1800 rpm

Several motors are permitted to be supplied by a single branch circuit as long as each motor is no larger than

1hp

A three-phase induction motor may have

2 poles

Horsepower is used to rate the

output capacity of a motor

The speed of a three-phase squirrel cage induction motor is controlled by the frequency of the applied voltage and

the number of poles

The most common service factor appearing on a motor's nameplate is

1.15

In a DC series motor, how much of its full-load torque is developed at starting?

500%

Any exposed live parts must be guarded if they are operating at

50V or more between terminals

In a split-phase motor, how much greater is the starting current when compared to the full-load current?

6 to 8 times

A medium-size motor has a frame number of 284T. The D dimension of this motor is

7"

A delta-connected motor has

9 leads

Which of the following motors is used when the required starting torque is high and speed control is desirable?

Compound

Which of the following is most likely to use dynamic braking?

Forklift

For a given number of poles, which of the following determines the speed of an AC motor?

Frequency

Which of the following motors is the best installation choice for an application requiring adjustable speeds?

Shunt DC

Which of the following motors provides constant speed from no-load conditions to full-load conditions?

Synchronous

According to NEMA definitions, which of the following is a type of totally enclosed motor?

Water-cooled

According to NEMA definitions, which of the following is a type of open motor?

Weather-protected

Which motor should be used for applications that require frequent starts without overheating the motor?

Wound rotor induction motor

The primary method of varying the speed on a DC shunt motor is to adjust the voltage and current on the field winding or the

armature

A typical constant-torque load would be a

conveyor

The stationary magnet of a DC motor is represented by the

field poles

The capacitor-start motor is the single-phase motor type that has the

highest starting torque

For a constant-torque load, the horsepower increases and decreases

in direct proportion to the speed

The value indicated in rpm on the nameplate is the

rated full-load speed

DC injection braking is used on

the stationary windings of AC motors

The terminals of a motor can be identified using a battery and a(n)

voltmeter

The NEC® requires motor disconnecting means be

within sight of the controller location