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Motor Control Center Fundamentals
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Motor Control Center Fundamentals
Motor Control Center Fundamentals
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1
Question
What serves as an efficient method to mount, power, and organize electrical motor control, automation, and power distribution systems?
Page 1
Answer
motor control center
2
Question
What are the typical dimensions of a standard motor control center section?
Page 1
Answer
20 inches wide by 90 inches tall, and 15 to 20 inches deep
3
Question
What should be consulted when installing, operating, or maintaining a motor control center?
Page 1
Answer
manufacturer’s manuals
4
Question
What wiring compartment is located at the top of a motor control center?
Page 2
Answer
top horizontal wireway
5
Question
What provides vertical wiring pathways in a motor control center?
Page 2
Answer
vertical wireway
6
Question
What are the plug-in modules called in a motor control center?
Page 2
Answer
unit or bucket
7
Question
What device provides isolation for each individual unit or bucket in a motor control center?
Page 2
Answer
individual unit (or bucket) disconnect switch
8
Question
What wiring compartment is located at the bottom of a motor control center?
Page 2
Answer
bottom horizontal wireway
9
Question
From which directions can feeder power enter a motor control center?
Page 2
Answer
overhead or underneath
10
Question
How are units or buckets of Size 3 or smaller wired in a Type C motor control center?
Page 4
Answer
factory-wired from unit-located terminal blocks to the master terminal blocks
11
Question
What materials are typically used for power buses in motor control centers?
Page 4
Answer
copper or aluminum
12
Question
What defines a Class 2 Type C motor control center?
Page 4
Answer
interconnecting units with Size 3 or smaller starters and terminations on terminal blocks mounted on the bottom of each vertical section
13
Question
What defines a Class 1 Type A motor control center?
Page 4
Answer
independent units with wiring connected directly to device terminals internal to the unit
14
Question
What defines a Class 2 Type B-D motor control center?
Page 4
Answer
interconnecting units with Size 3 or smaller starters and load wiring connected to factory-wired power terminals located immediately adjacent to and accessible from the vertical wireway
15
Question
How do Class 1 Type A and Class 2 Type C motor control centers differ in unit structure and wiring?
Page 4
Answer
Class 1 Type A has independent units with wiring directly to internal device terminals; Class 2 Type C has interconnecting units with Size 3 or smaller starters and terminations on bottom-mounted terminal blocks in vertical sections
16
Question
What installation mechanism is used by removable units or buckets in motor control centers?
Page 4
Answer
sliding track and mechanical lever
17
Question
What transformers condition voltage and current levels in motor control center metering compartments?
Page 4
Answer
potential and current transformers
18
Question
What is the purpose of potential and current transformers in MCC metering compartments for metering devices?
Page 4
Answer
to condition voltage and current levels
19
Question
What components comprise the motor control compartment of a fixed MCC bucket?
Page 5
Answer
disconnect, primary fuses, starter, secondary fuse, circuit breaker, push buttons, terminal block
20
Question
What coating protects copper buses from corrosion in motor control centers in corrosive atmospheres?
Page 5
Answer
tin
21
Question
What function does the defeater mechanism or interlock serve on an MCC unit or bucket door?
Page 6
Answer
prevents the door from being opened when the disconnect switch or circuit breaker is on and the unit is energized
22
Question
What offers the primary protection against environmental elements for a motor control center?
Page 6
Answer
NEMA or IEC enclosure
23
Question
What surface condition is required for motor control center installation regardless of factory assembly?
Page 6
Answer
level surface
24
Question
What does the presence of ozone odor indicate when performing maintenance on a motor control center?
Page 6
Answer
arcing
25
Question
What does discoloration of bolted electrical connections and insulation indicate on an MCC during maintenance?
Page 7
Answer
overheating
26
Question
What procedure applies to buckets during annual motor control center maintenance?
Page 7
Answer
buckets should be drawn out or removed from the MCC
27
Question
What maintenance tasks are required for air filters during annual MCC inspections?
Page 7
Answer
inspect, clean, or replace air filters
28
Question
Which MCC class and type features independent units with direct wiring to internal device terminals?
Page 4
Answer
Class 1 Type A
29
Question
Which MCC class and type has terminal blocks mounted on the bottom of each vertical section?
Page 4
Answer
Class 2 Type C
30
Question
Which MCC class and type uses factory-wired power terminals adjacent to the vertical wireway?
Page 4
Answer
Class 2 Type B-D