Deck 6: Limit Switches and Phase Failure Relays

Question 1

If two of the lines supplying power to a three-phase motor are reversed, the motor will not reverse the direction of rotation.

Answer 1

False

Question 2

Motors are intended to operate on systems with balanced voltage.

Answer 2

True

Question 3

The percentage of heat rise in the motor caused by the voltage unbalance is equal to ____ times the percent squared.

A) two
B) three
C) four
D) five

Answer 3

two

Question 4

____________________ phasing will cause the two phases that remain energized in a three-phase motor to increase current by an average of 173 percent.

Question 5

NEMA recommends that the unbalanced voltage not exceed plus or minus ____________________ percent.

Question 6

What problems can unintended reversal of direction cause?

Question 7

Discuss unbalanced voltage.

Question 8

Limit switches are used to detect when an object is present or absent from a particular location.

Question 9

Micro switches are used in small spaces that would never be accessible to a larger device.

Question 10

The type of bumper arm used is determined by the ____ of the limit switch.

A) location
B) contact arrangement
C) application
D) size

Question 11

Electrical ratings for the contacts of the basic micro switch are generally in the range of ____ volts AC.

A) 75
B) 100
C) 150
D) 250

Question 12

What is the role of bumper arms?

Question 13

Describe the subminiature micro switch.