Motor Control Centers, Contactors, and Motor Starters

Question 1

Knife switch improvements including insulated handles and spring-loaded blades mounted inside steel enclosures evolved into the modern ___.

A) breaker
B) disconnect switch
C) overload
D) relay

Answer 1

B) disconnect switch

Question 2

When performing maintenance on an MCC, what does the presence of an ozone odor indicate?

A) Arcing
B) Open circuit
C) Overheating

Answer 2

A) Arcing

Question 3

In corrosive atmospheres, copper buses in MCCs are often coated with ___ to protect the bus from corrosion.

A) carbon
B) tin
C) zinc

Answer 3

B) tin

Question 4

Metering compartments in MCCs often require the use of ___ and ___ transformers to condition voltage and current levels for metering devices.

A) control / current
B) differential / auto
C) potential / current

Answer 4

C) potential / current

Question 5

A ___ is a magnetically activated switching device (without overload protection attached) and is used to switch single-phase or 3-phase AC power, or DC power to the load.

A) definite purpose magnetic contactor
B) magnetic contactor
C) magnetic motor started
D) manual contactor

Answer 5

B) magnetic contactor

Question 6

What is the maximum HP for a 3-phase, 480-volt motor that can be controlled using a size 3 NEMA contactor?

A) 25
B) 40
C) 50
D) 75

Answer 6

C) 50

Question 7

Class ___ overload relay operation is often used with hermetically-sealed motors, submersible pumps, or motors with short locked rotor time capability.

A) 10
B) 20
C) 30

Answer 7

A) 10

Question 8

Exhaust fans, small drill presses, and commercial garbage disposals are some common examples of typical fractional horsepower motors that would be controlled by ___.

A) definite purpose magnetic contactors
B) magnetic contactors
C) magnetic motor starters
D) manual motor starters

Answer 8

D) manual motor starters

Question 9

The secondary fuses or circuit breakers located on the line and load sides of the control transformer protect what part of the motor circuit?

A) Control circuit components
B) Motor branch circuit conductors
C) Motor windings or motor

Answer 9

A) Control circuit components

Question 10

The ___ should be used to install, operate, or maintain an MCC.

A) manufacturer’s manuals
B) NEC
C) project specifications

Answer 10

A) manufacturer’s manuals

Question 11

Overloads are sized based on motor full load current (FLC), contactor size, the motor service factor (SF), ambient temperature, and the class number requirement.

A) True
B) False

Answer 11

A) True

Question 12

A(n) ___ overload relay monitors the current in the motor power circuit through the use of small built-in current transformers.

A) electronic
B) magnetic
C) thermal

Answer 12

A) electronic

Question 13

Match the components of a square D motor starter

Answer 13

A - Coil
B - Contactor
C - Overload relay
D - Auxiliary contact
E - Contact block
F - Magnetic pole piece
G - Overloads

Question 14

The power poles in the starter carry the motor current while other contacts, called ___, are used for the control circuit.

A) auxiliary contacts
B) extra contacts
C) magnetic contacts
D) manual contacts

Answer 14

A) auxiliary contacts

Question 15

A motor ___ condition most often results from the loss of a phase on a 3-phase system, operation of the motor with too much load, or low line voltage to the motor.

A) ground fault
B) overload
C) short circuit

Answer 15

B) overload

Question 16

The NEMA or IEC enclosure is the primary protection from the environmental elements.

A) True
B) False

Answer 16

A) True

Question 17

Overload relays protect which part of the motor circuit?

I. The conductors
II. The control circuit components
III. The motor windings or motor

A) I.
B) I. and II.
C) I. and III.
D) II. and III.

Answer 17

C) I. and III.

Question 18

If the manufacturer assembled the MCC on a level surface, then installing the MCC on a level surface is not necessary.

A) True
B) False

Answer 18

B) False

Question 19

The defeater mechanism screw or interlock on the door of an MCC unit or bucket serves to prevent the door on the bucket from being opened when the disconnect switch or circuit breaker is on and the unit is energized.

A) True
B) False

Answer 19

A) True

Question 20

If a worker was replacing an AC-3, 30 A IEC contactor with a NEMA contactor, what size contactor would be replaced?

A) Size 1
B) Size 2
C) Size 3
D) Size 4

Answer 20

B) Size 2

Question 21

When performing maintenance on an MCC, what does discoloration of bolted electrical connections and insulation indicate?

A) Arcing
B) Open circuit
C) Overheating

Answer 21

C) Overheating

Question 22

___ devices are smaller, less expensive, and more application-specific.

A) IEC
B) NEMA

Answer 22

A) IEC

Question 23

Motor operation above the full load current over time can cause a(n) ___ condition that increases the winding temperature, which damages the wire insulation and shortens motor life.

A) ground fault
B) overload
C) short circuit

Answer 23

B) overload

Question 24

The newest overload technology, ___ overload devices, provides motor protection and control flexibility not available in the other two types of overload relays.

A) electronic
B) magnetic
C) thermal

Answer 24

A) electronic

Question 25

Lighting contactors are generally rated for ___ to ___.

A) 10 A / 15 A
B) 15 A / 20 A
C) 20 A / 30 A
D) 20 A / 40 A

Answer 25

B) 15 A / 20 A