Deck 21: Motor Installation

Question 1

Starter sizes are rated by motor type and horsepower only.

Answer 1

False

Question 2

It is not uncommon to employ larger size starters than those listed in starter size and rating charts. This is especially true when using IEC-type starters because of their smaller load contact size.

Answer 2

True

Question 3

Although it is permissible to used non-time-delay fuses and instantaneous-trip circuit breakers, most motor circuits are protected by dual-element time-delay fuses or ____-time circuit breakers.

A) half
B) reverse
C) inverse
D) converse

Answer 3

C

Question 4

If for some reason a fuse will not permit a motor to start without blowing, NEC 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) 125
B) 175
C) 200
D) 225

Question 5

If a motor nameplate lists code letters that range from A to V, they indicate the type of rotor bars used when the rotor was made.

Question 6

If an NEC table lists a full-load current of 77 amperes for a particular motor, and the value of current is increased by 25% for the calculation of the conductor current, what is the proper formula for this calculation?

A) 77 x 0.25 = 19.25 amperes
B) 77 x 1.25 = 96.25 amperes
C) 77 x 25 = 1925 amperes
D) 77 x 125 = 9625 amperes

Question 7

The two most common ratings bodies for starter sizes are ____ and IEC.

A) NEMA
B) NECO
C) NAM
D) NADO

Question 8

Most common squirrel-cage motors used in industry actually fall in the Design ____ classification, and for purposes of selecting a short-circuit protective device, are considered to be this design classification unless otherwise listed.

A) B
B) C
C) H
D) J

Question 9

Like single-phase motors, two-phase motors, which are especially designed for low-speed, high-torque applications and multispeed motors, use the nameplate rating instead of the values shown in the appropriate NEC table.

Question 10

When determining the overload size for a motor, the nameplate current rating of the motor is used instead of the current values listed in the NEC tables.

Question 11

The code states that the rating or setting of a short-circuit protective device shall not be greater than the largest rating or setting of the largest branch circuit short-circuit and ground-fault protective device for any motor supplied by the feeder plus the sum of the full-load running currents of the other motors connected to the feeder.

Question 12

NEC tables list the amount of current that a motor is expected to draw under an average load condition.

Question 13

According to NEC 110.14(C), a conductor is to be selected and coordinated as to not exceed the ____ temperature rating of any connected termination, any connected conductor, or any connected device.

A) lowest
B) average
C) highest
D) stated

Question 14

Motors manufactured before 1986 do not generally contain a NEMA design letter.

Question 15

If a 60-hp, 460-volt two-phase motor has a phase current of 67 amperes, what is its neutral current?

A) 94.5 amperes
B) 116 amperes
C) 149.8 amperes
D) 164.1 amperes

Question 16

A 250-hp squirrel-cage induction motor is connected to a 560-volt line. The motor has a nameplate current of 232 amperes and a service factor of 1. NEC Table 430.32(A) indicates that the full-load current should be increased by a factor of 115%. What is the overload size for this motor?

A) 34.8 amperes
B) 226.8 amperes
C) 247 amperes
D) 644 amperes

Question 17

NEC 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) 110
B) 125
C) 150
D) 200

Question 18

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

A) 2
B) 3
C) 5
D) 6

Question 19

If the largest fuse size of three motors is 200 amperes, and the running currents of the other two motors are 77 amperes and 27 amperes, the fuse size for the main feeder is (200 + 77 + 27) / 3 = 101 amperes.

Question 20

As a general rule, the temperature rating of most devices will not exceed 75 degrees C.