Deck 21: Motor Installation

Question 1

Figure 21-2
A 3-hp single-phase AC motor is connected to a 208-volt line. What will be the full-load running current of this motor? Use the accompanying figure.

A) 4.1 A
B) 16 A
C) 18.7 A
D) 30.8 A

Answer 1

C

Question 2

Figure 21-10
A 15-hp, three-phase squirrel-cage motor with a code letter of K is connected to a 240-volt line. Determine the locked-rotor current using the accompanying figure.

A) 245.1
B) 266.7
C) 287.4
D) 306.7

Answer 2

D

Question 3

Figure 21-4
A 150-hp, 460-volt synchronous motor is to be operated at 80% power factor. What will be the full-load current rating of the motor? Use the accompanying figure.

A) 66
B) 81
C) 127
D) 189

Answer 3

D

Question 4

Figure 21-14
A 40-hp three-phase squirrel cage motor is connected to a 208-volt line. What is the minimum size NEMA starter that should be used to connect this motor to the line? Use the accompanying figure.

A) 00
B) 1
C) 2
D) 4

Question 5

Figure 21-10
Most motor circuits are protected by ____.

A) instantaneous-trip circuit breakers or inverse-time circuit breakers
B) instantaneous-trip circuit breakers
C) dual-element time-delay fuses or inverse-time circuit breakers
D) non-time delay fuses

Question 6

Figure 21-4
A 200-hp, 2300-volt synchronous motor is to be operated at 90% power factor. What will be the full-load current rating of this motor? Use the accompanying figure.

A) 44
B) 48
C) 52
D) 56

Question 7

Figure 21-14
If for some reason this fuse will not permit the motor to start without blowing, NEC Section 430.52(C)(1) Exception 2(b) states that the rating of a dual-element time delay fuse may be increased to a maximum of ____ of the full-load motor current.

A) 75%
B) 115%
C) 175%
D) 225%

Question 8

The size of the short-circuit protective device is determined by Section 430.62(A).

Question 9

All heater sizes are chosen from a chart supplied by the starter manufacturer.

Question 10

Figures 21-4 and 21-12
A 100-hp three-phase squirrel-cage induction motor is connected to a 240-volt line. The motor does not contain a NEMA design code. A dual-element time delay fuse is to be used as the short-circuit protective device. Use the accompanying figure to determine the size needed.

A) 350 A
B) 400 A
C) 450 A
D) 500 A

Question 11

As a general rule the temperature rating of most devices will not exceed ____ degrees C.

A) 45
B) 55
C) 65
D) 75

Question 12

Different tables from the ____ (NEC®) are used to determine the running current for the different types of motors.

A) National Engineering Council
B) National Electrical Code®
C) National Electrical Council
D) National Engineering Code

Question 13

Starter sizes are rated by motor type, horsepower, and connected voltage.

Question 14

When the termination temperature rating is not listed or known, for circuits rated at 100 amperes or less, or for #14 AWG through #1 AWG conductors, the ampacity of the wire, regardless of the temperature rating, must be selected from the 60°C column.

Question 15

There are two basic methods for determining the locked-rotor current (____ current) of a squirrel-cage induction motor depending on the information available.

A) starting
B) running
C) stopping
D) nameplate

Question 16

Figure 21-2
When using a two-phase, three-wire system, the size of the neutral conductor must be increased by the square root of ____.

A) 1.5
B) 2
C) 3
D) 5

Question 17

Two-phase motors use the nameplate rating instead of the values shown in the table for full-load currents.

Question 18

Figures 21-4 and 21-12
The two most common starter size ratings are NEMA and ____.

A) NIST
B) NFPA
C) UL
D) IEC

Question 19

Motors especially designed for low speed and high torque, or multispeed motors, shall have their running current determined from the ____.

A) starting speed
B) attached overload protection device
C) nameplate rating
D) NEC tables

Question 20

Section 430.22(A) states that conductors supplying a single motor shall have an ampacity of not less than ____% of the motor full-load current.

A) 90
B) 125
C) 155
D) 200