Motor Control Centers, Contactors, and Motor Starters Flashcards
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
B) disconnect switch
When performing maintenance on an MCC, what does the presence of an ozone odor indicate?
A) Arcing
B) Open circuit
C) Overheating
A) Arcing
In corrosive atmospheres, copper buses in MCCs are often coated with ___ to protect the bus from corrosion.
A) carbon
B) tin
C) zinc
B) tin
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
C) potential / current
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
B) magnetic contactor
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
C) 50
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
A) 10
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
D) manual motor starters
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
A) Control circuit components
The ___ should be used to install, operate, or maintain an MCC.
A) manufacturer’s manuals
B) NEC
C) project specifications
A) manufacturer’s manuals
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
A) True
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
A) electronic
Match the components of a square D motor starter
A - Coil
B - Contactor
C - Overload relay
D - Auxiliary contact
E - Contact block
F - Magnetic pole piece
G - Overloads
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
A) auxiliary contacts
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
B) overload
The NEMA or IEC enclosure is the primary protection from the environmental elements.
A) True
B) False
A) True
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.
C) I. and III.
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
B) False
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
A) True
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
B) Size 2
When performing maintenance on an MCC, what does discoloration of bolted electrical connections and insulation indicate?
A) Arcing
B) Open circuit
C) Overheating
C) Overheating
___ devices are smaller, less expensive, and more application-specific.
A) IEC
B) NEMA
A) IEC
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
B) overload
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
A) electronic
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
B) 15 A / 20 A
