UNIT 36 REVIEW QUESTIONS ANSWER KEY GO BACK TO INDEX
36-1) What is a relay?
36-2) When checking the resistance of the different parts of a relay, what
resistance should you expect for the coil, normally open contacts, and normally
closed contacts?
36-3) What is the difference between a light-duty and a heavy-duty relay?
36-4) What is a reduced voltage starter?
36-5) What are the three current ratings found on a contactor?
36-6) Why do contacts snap open and close with spring assist?
36-7) Where are thermal bimetal overloads often used?
36-8) What is an advantage of a magnetic overload relay?
36-9) List the causes of excessive motor heating.
Among the causes of excessive heating are the following:
36-10) List the different types of motor overload devices.
The various types of overload devices are as follows:
Motor starter
36-11) How does a line break overload device differ from a single phase and three-
phase motor?
36-12) What is the difference between a relay and a contactor?
36-13) What is the difference between a contactor and a magnetic starter?
36-14) Why is the contact surface in relays and contactors coated with a special
coating of very conductive material?
36-15) What is the most common cause of motor failure?
36-16) According to Table 36-1, what is the upper and lower limit of a motor with
the voltage of 460 V?
36-17) List the three types of protective devices used to protect the motor against
excessive heat.
36-18) Describe how a pilot-duty overload relay operates.
Pilot-duty overloads operate like relays. They have a separate coil and contacts.
36-19) What is the advantage of manual reset?
36-20) What overload protection does an external supplemental overload device
provide?
36-21) List the major components of a variable frequency drive.
A variable frequency drive is a system for controlling the rotational speed of an
36-22) What is meant by pulse width modulation?
36-23) What are the three terminals of an IGBT and how does it function?
36-24) What are the basic circuit components for a low-pass filter?
36-25) What is harmonic distortion and what are its effects?