Deck 3: The Control Transformer, Relays, Contactors, and Motor Starters

Question 1

Most industrial motors operate on voltages that range from 240 to 480 volts.

Answer 1

True

Question 2

NEC Section 430.72(C) lists requirements for the protection of transformers employed in motor control circuits.

Answer 2

True

Question 3

Control transformers generally have ____ terminals connected to the primary and secondary leads.

A) barrier
B) luster
C) block
D) screw

Answer 3

screw

Question 4

It is a common practice to not ground one side of the control transformer. This is generally referred to as a ____ system.

A) rated
B) floating
C) ghost
D) fused

Question 5

The ____________________ rating of control transformers generally ranges from 0.75 kilovolt-amperes, or 75 volt-amperes, to 1 kilovolt-ampere, or 1000 volt-ampere.

Question 6

How are control transformers protected?

Question 7

What are ghost voltages?

Question 8

Relays are electromechanical switches that lack auxiliary contacts.

Question 9

The greatest difference between relays and contactors is the fact that contactors are equipped with large contacts that are intended to connect high-current loads to the power line.

Question 10

Mechanically held contactors and relays are often referred to as ____ contactors or relays.

A) vacuum
B) coil clearing
C) sequenced
D) latching

Question 11

Solid-state relays that are intended to connect alternating current loads to the line use a device called a(n) ____________________.

Question 12

The number of ____________________ refers to the load contacts and does not include the number of control or auxiliary contacts.

Question 13

What problems can insufficient coil voltage cause?