Deck 13: Starting Three-Phase, Squirrel-Cage Induction Motors

Question 1

NEC® requirements regarding starting protection for squirrel-cage induction motors state: The maximum size of fuses permitted to protect motors are rated at 300% of the ____________________ current of the motor for nontime-delay fuses, and 175% for time-delay fuses.

Answer 1

full-load
full load

Question 2

Which type of diagram is preferred by many electricians when troubleshooting, and why?

Answer 2

Many electricians find it easier to troubleshoot from a schematic, or elementary, diagram, as it shows the electrical sequence of operation more clearly.

Question 3

Connecting thermal sensors, called ____________________, are used in an overload monitoring system designed to measure the amount of current flowing to the motor through the contactor.

Answer 3

heaters

Question 4

What are the main components of a magnetic switch used for starting a three-phase AC motor?

Question 5

Motors can be automatically controlled by using a magnetic starter or may be manually controlled by using a(n) ____________________ type of controller.

Question 6

Which type of diagram shows physical location as well as general wire routing?

Question 7

The magnetic switch is called a motor starter if it has overload protection.

Question 8

____________________ refers to the simplest starting arrangement in which the three-phase AC motor is connected across full line voltage for operation in one direction of rotation.

Question 9

Referring to the various types of rotor construction and associated code letters, code letter A has high starting torque and relatively low starting current.

Question 10

If the motor controller is in a higher ambient temperature than the motor it controls, what adjustment should be made by an electrician when choosing the correct heater size?

Question 11

The National Electrical Code® requires the use of two overload units as running-overload protection Table 430.37.

Question 12

In addition to the standard contacts, a starter may be provided with externally attached auxiliary contacts, sometimes called ____________________.

Question 13

In general terms, explain two ways that auxiliary contacts are used.

Question 14

To reverse the direction of rotation of three-phase motors, interchange any three of the four line lead connections to the motor terminals.

Question 15

In the case of 125% or 115% overload thermal protection, the Code does allow the electrical personnel to increase the ratings if the original selection does not allow the motor to operate.