Deck 10: Motor Installation

Question 1

The temperature ratings of devices such as circuit breakers, fuses, and terminals are found .

A) on the nameplate
B) in the NEC tables
C) in UL product directories
D) through individual testing

Answer 1

C

Question 2

What percentage of the full-load current of a thermally protected continuous-duty motor of more than one hp can the trip current be, if the full-load current is 15 amperes?

A) 122
B) 140
C) 156
D) 170

Answer 2

C

Question 3

Which NEC table lists the running currents for single-phase ac motors?

A) 430.247
B) 430.248
C) 430.249
D) 430.250

Answer 3

B

Question 4

How does temperature rating impact conductor size selection?

Question 5

A 100-horsepower, three-phase squirrel-cage induction motor is connected to a 240-volt line. A dual-element time- delay fuse is to be used as the short-circuit protective device. What is the correct fuse rating?

A) 300
B) 350
C) 400
D) 450

Question 6

Two-phase motors that are especially designed for applications use the same rules for determining full-load currents as single-phase motors.

A) high speed-high torque
B) low speed-high torque
C) high speed-low torque
D) low speed-low torque

Question 7

The voltages of a two-phase system are degrees out of phase with each other.

A) 90
B) 120
C) 150
D) 180

Question 8

The starting current of a squirrel-cage motor can be determined by multiplying the kVA rating by the rating and then dividing by the applied voltage.

A) nameplate
B) horsepower
C) locked-rotor
D) resistance

Question 9

A 150-horsepower, three-phase squirrel-cage induction motor is connected to 440 volts. The motor nameplate lists the following information:
Amps 175
SF 1.25
NEMA code B
The conductors are to be copper with type THHN insulation. The short-circuit protective device is to be an inverse- time circuit breaker. The termination temperature rating is not known.
Determine the conductor size and overload size.

Question 10

motors are often made to have a leading power factor by overexcitation of the rotor current.

A) Unity
B) Squirrel-cage
C) Wound-rotor
D) Synchronous

Question 11

The motor overload size is to be determined by using the current listed .

A) on the nameplate
B) in the NEC tables
C) in the UL tables
D) on the stator

Question 12

A 25-horsepower, three-phase induction motor has a nameplate rating of 32 amperes. The nameplate also shows a temperature rise of 30 degrees C. What is the overload size for this motor in amperes?

A) 20
B) 30
C) 40
D) 50

Question 13

When a two-phase, three-wire system is used, the size of the neutral conductor must be increased by .

A) the square root of two
B) two
C) the square root of three
D) three

Question 14

What should be done if a dual-element time-delay fuse will not let the motor start?

Question 15

What is the relationship between the rotor bars of a squirrel-cage motor and the starting current?

Question 16

A one-horsepower motor will have a full-load current of amperes when connected to 90 volts dc.

A) 6.8
B) 9.5
C) 9.6
D) 12.2

Question 17

What is included in the NEC motor tables, and how is this information used?

Question 18

Most common squirrel-cage motors used in industry fall into the design classification.

A) A
B) B
C) C
D) D

Question 19

Most motor circuits are protected by dual-element time-delay fuses or .

A) dual-time circuit breakers
B) instantaneous trip circuit breakers
C) nontime delay fuses
D) inverse-time circuit breakers

Question 20

If a synchronous-type motor is operated at 90 percent power factor, the rated full-load current in the table is to be ____.

A) decreased by 90%
B) decreased by 10%
C) increased by 10%
D) increased by 90%