EMC 225 motor control Flashcards
What is motor control
refers to the components and wiring of ccts used to start,stop and reverse, change speed of motors
What do typical motor ccts include
-power-rated devices to switch the motor or other power load
-overcurrent protection for power ccts and control ccts
-overload protection for the motor
What are 2 main types of starters
-manual
-electromagnetic
What is a combination starter
has a electromagnetic starter and a disconnect switch within an enclosure
What is a controller in a motor
-device or group of devices that regulate the operation of the apparatus to which is connected
What does a controller in a motor control do
-direction of rotation
-speed
-speed of acceleration or deceleration
What does murphys law state
if something can possiblt go wrong, it eventually will
In addition to actually controlling motor operation, motor control cct may include what other features?
-manual or automatic control devices
-indicators
-meters or displays
-saftey features to protect personelle
-preventative functions to avoid or limit equipment damage when abnormal condictions
motor control equipment is often applied to other types of power loads. What are 2 examples
-high capactity heating elements
-groups of light fixtures
What are these motor cct components used for?
a)manual starters and contactors
b)indicators
c)warning horns and lights,lockabke diconnects, ect.
a) switch the motor or other power load
b)visual information of status of equipment and allow remote monoriting
c)warn workers that equipment is about to start.lockable disconnects provide a isolation poing for workers that could be injured or killed if equipment was energized
What does an overload in a motor mean
-exxessive load current that will overheat conductors and equipment if it continues to run.
What does a short cct in a motor refer to
very high current associsated with a low impedance fault.
What is fault current and interrupting capacity?
-overcurrent device that provides short- cct protection and must be able to inturupt the max voltage and fault current the supply can provide
what code rule talks about ratings of protective and control equipment
14-012
Overcurrent protection refers to the ______________ that automatically opens the cct when the current exceeds a certain value
device
In ccts that do NOT supply motors how is the overcurrent device selected?
to provide both overload and short cct protection
-doesnt exceed the safe current rating of conductors or connectedf equipment
In motor ccts the overcurrent device is selected to carry the __________________- without ttripping and provide _________________ for the conductors and equipment
-motor starting current
-short-cct protection
What are diconects for a motor
-saftey devices where the load is a hazardous electrically and mechanically.
The number and loaction of diconnects in motors must satisfy which CEC rules
28-600,602,604
What are the requirements for a manually operated switch or breaker
-opens all ungrounded lines at the same time
-within sight
-9m of the motor and/or locked in the open position using an approved locking device
Air conditioning and refrigeration equipment must have a diconnect within ____________
3m
You must isolate the motor at the ___________-
diconnect
In a system with ________ the motor is automatically disconnected from the supply with the line voltage dips velow a “hold-in value” and is automatically restarted when the voltage returns to normal
low-voltage release
In a system with _____________ the motor is automatically disconnected from the supply when the line voltage dips velow the “hold-in” value and is NOT automatically restarted when the voltage returns to normal
low-voltage protection