A ________ is a mechanism used to safely start and stop the motor, and also to provide some running protection for the motor
Motor Starter
The ________ is a rotary-action selector switch commonly used to manually control speed and to change the directions of motors
Drum switch
To guard against overload currents, motor starters use protective devices called ________
Overload relays
Name the three electrical ratings for manual motor starters
Voltage, ampacity, and horsepower
List two types of manual motor starters
Toggle switch and push button
The two most common types of overload protection are ________ and ________
Melting-alloy relays (solder-pot relay) and bimetallic strip overload relays
There are two important characteristics of AC induction motors. What are they?
- Motors draw large, momentary in-rush currents when they are switched on
- If the mechanical load (output) of a motor is increased, motor current also increases
All motor starting switches contain ________, which allows the switch to safely interrupt the in-rush current or locked rotor current of the motor
Horsepower-rated contacts
True or false: similar to toggle switches, drum switches come with horsepower-rated contacts and provide overload protection.
False. The contacts of the drum switch are horsepower-rated, but the drum switch itself does not provide overload protection. Additional overload protection must be provided
Briefly describe the difference between low voltage release and low voltage protection, and the advantages and dangers of both
Low voltage release means that during a power failure, a motor will automatically restart when power is restored. This is desirable in the case for motors connected to fans, blowers, pumps, and oil-burners. But for equipment such as saws, lathes, and equipment that might harm an operator during an unexpected startup, this automatic start-up is a hazard. Low voltage protection guards the equipment so that it cannot automatically restart after loss of power
True or false: manual starters do not provide low voltage protection
True
What part of a simple motor starter senses an overload current drawn by the motor?
The heater element of the overload relay
A melting-alloy type of thermal overload relay is called a ________
Solder-pot relay
An overload relay that uses a strip of two dissimilar metals is called a ________
Bimetallic relay
The fundamental purpose of any motor starter is to ________, and to ________
Safely start and stop the motor, and to provide running (overload) protection for the motor
A(n) ________ magnetic motor starter uses full-line voltage to start the motor
Across-the-line
What two important safety steps must be taken before starting work on a motor branch circuit?
- Disconnect the power source, and 2. Lock out and tag the disconnecting means
Before energizing a motor, it is advised first to test electrically with a ________
Megger
________ is a huge rush of current over a short period of time (fractions of a second)
Over current
________ is a gradual rise in the value of current which causes damage due to excessive heating
Overload
Manual and magnetic motor starters use ________ types of overload protection
Thermal
Which two basic components make up an overload relay?
Heater element, and a normally closed auxiliary contact
What are the two most common types of thermal overload devices?
Melting solder pot, and bimetallic strip
True or false: overload relays are sensitive to excessively high and low ambient temperatures
True. If the OLR is installed in a very hot environment, it may trip before a dangerous amount of current is sensed, (nuisance tripping). If the OLR is installed in a very cold environment, then the OLR may not trip even through a dangerous level of current is flowing in the motor
