Question 1

Starter sizes are rated by motor type and horsepower only.

Accepted Answer

Starter sizes are determined by various factors including motor type, horsepower, voltage, and application requirements, not just motor type and horsepower.

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.

Accepted Answer

This statement is true. Larger size starters may be employed than those listed in starter size and rating charts when using IEC-type starters due to their smaller load contact size.

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.

Accepted Answer

Motor circuits require a high inrush current for a short period of time during start-up. Non-time-delay fuses and instantaneous-trip circuit breakers may falsely trip during this high inrush period, leading to unnecessary downtime and maintenance. Dual-element time-delay fuses or inverse-time circuit breakers provide a delayed response to this inrush current and are better suited for protecting motor circuits. The correct answer is "C) inverse" as it refers to the type of circuit breaker that provides a delayed response to the inrush current.

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.

Accepted Answer

According to NEC 430.52(C)(1) Exception 2(b), the rating of a dual-element time-delay fuse may be increased to a maximum of 225% of the full load motor current.

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.

Accepted Answer

Code letters on a motor nameplate do 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?

Accepted Answer

The proper formula to calculate the conductor current for a motor with a full-load current of 77 amperes and a 25% increase is 77 x 1.25 = 96.25 amperes.

Question 7

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

Accepted Answer

NEMA and IEC are the two most common ratings bodies for starter sizes. NECO, NAM, and NADO are not commonly used ratings bodies for starter sizes.

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.

Accepted Answer

Design B squirrel-cage motors are the most common type used in industry due to their general-purpose characteristics, including moderate starting torque and low starting current. They are typically considered Design B unless otherwise specified.

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.

Accepted Answer

Two-phase motors and multispeed motors use the nameplate rating instead of the values shown in NEC table, just like single-phase motors.

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.

Accepted Answer

The nameplate current rating provides the actual current draw of the specific motor, whereas the current values listed in the NEC tables are general guidelines for wiring and protection of electrical equipment.

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.

Accepted Answer

This statement is true according to the National Electrical Code.

Question 12

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

Accepted Answer

NEC tables provide information on electrical code requirements, but do not provide specific information on motor current draw under load conditions. This information would be found in the motor manufacturer's specifications or empirical testing.

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.

Accepted Answer

The correct answer is A) lowest, because NEC 110.14(C) specifies that the conductor must be selected so as not to exceed the lowest temperature rating among any connected terminations, conductors, or devices to ensure safe operation and prevent overheating.

Question 14

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

Accepted Answer

The answer of Motors manufactured before 1986 do not generally...

Question 15

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

Accepted Answer

In a two-phase system, the neutral current is calculated using the formula: Neutral Current = √2 * Phase Current. Therefore, Neutral Current = √2 * 67 = 94.5 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?

Accepted Answer

The answer of A 250-hp squirrel-cage induction motor is connected...

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.

Accepted Answer

NEC 430.22(A) states that conductors for a single motor must have an ampacity of at least 125% of the motor full load current to ensure that the motor has sufficient current to operate and to account for starting current.

Question 18

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

Accepted Answer

The size of the neutral conductor in a two-phase, three-wire system must be increased by the square root of 2 because the maximum unbalanced current in the neutral can be √2 times the phase current due to the phase difference between the two phases.

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.

Accepted Answer

The correct calculation for determining the fuse size for the main feeder is to take the largest fuse size and add 25% of the sum of the other two. Therefore, the calculation would be: 200 + (77+27)*0.25 = 216.5, which would be rounded up to the nearest standard fuse size, which is 225 amperes.

Question 20

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

Accepted Answer

Most devices are designed to operate within the temperature range of 0-75 degrees C to ensure reliable performance and prevent damage to the internal components. However, there may be some exceptions where devices are designed to operate at higher temperatures, but this is not a general rule.

Quiz 21: Motor Installation