IEC Motors and Motor Controls 4

Question 1

A motor disconnecting means must be within sight of the motor and its driven machinery. 'Within sight' is defined by the NEC as visible and not more than:

Accepted Answer

50 feet

Answer

Per NEC 430.102, 'within sight' means visible and not more than 50 feet distant from the motor and driven machinery.

Question 2

What is plugging as a method of motor braking?

Accepted Answer

Reversing the phase sequence of the motor while it is running to create braking torque

Answer

Plugging reverses the phase sequence applied to the motor while it is still rotating, creating a reverse rotating field that produces braking torque.

Question 3

Which of the following best describes a split-phase motor?

Accepted Answer

A single-phase motor with two windings (main and auxiliary) displaced in time and space to create a rotating field

Answer

Split-phase motors use a main running winding and an auxiliary starting winding with different impedances to create phase displacement and a rotating magnetic field.

Question 4

What is the primary advantage of a capacitor-start motor over a standard split-phase motor?

Accepted Answer

Higher starting torque due to greater phase displacement between windings

Answer

The capacitor in the starting circuit creates nearly 90° phase displacement between the main and auxiliary winding currents, producing significantly higher starting torque.

Question 5

In a motor control ladder diagram, the symbol for a normally open (NO) contact that is controlled by a pushbutton is:

Accepted Answer

Two vertical lines with a diagonal line between them representing the actuator

Answer

In ladder diagrams, a normally open pushbutton contact is represented by two vertical lines (the contact symbol) with a slanted line representing the actuator arm.

IEC - Independent Electrical Contractors Practice Test

IEC - Independent Electrical Contractors Practice Test

IEC Motors and Motor Controls 4