Unit 18 Application of Motors Flashcards
Is Luis an egg head
True or fals
True
Power supply data should include the following information
The voltage, the current capacity in amperes, the frequency in hertz (cps), and the phase (single or three).
The voltage range for an electric motor is usually within +or-
10%
If an electric motor is rated for 208 V, the maximum allowable voltage would be _____, and the minimum allowable voltage would be _____.
228.8 V, 187.2 V.
how a service technician can tell if a compressor motor is drawing the proper amperage when it is running.
The technician can take an amperage reading while the motor is operating under load and compare that reading to the FLA on the nameplate. * Also, he must know the operating conditions of the motor.
In the United States, the frequency in cycles per second (cps) at which an AC electric motor operates under normal conditions is
60
Three-phase motors are often used in air-conditioning systems in residences.
True or false
False
Two types of bearings commonly used on small motors are
Sleeve and ball bearings.
An open single-phase motor with a centrifugal starting switch may not be used in
An area where explosive gasses exist.
service factor of the motor is a multiplier applied to the motor HP. It indicates how much the motor can run overloaded on a continuous basis w/ out damaging the motor winding
True or false
True
How does the insulation factor of a motor affect its use?
The insulation type or class (factor) of a motor allows a motor to operate at higher or lower ambient temperatures.
A ______ bearing surface must be used in a vertical shaft motor application.
Thrust
Two primary electric motor mount characteristics are
Rigid mount and resilient mount (rubber).
NEMA has established standardized motor dimensions. NEMA stands for
National Electrical Manufacturers Association.
Two types of motor drives are
Belt drive and direct-drive (coupling or mounted to motor shaft).
What is a matched set of belts?
A matched set of belts means the belts are exactly the same length.
Name the different types of belts.
“A” width belts and “B” width belts. (OR smooth grip and “tractor tire” grip belts)
Why must direct-drive couplings be aligned?
If direct-drive couplings are out of alignment, vibration will occur, which results in excessive wear.
An instrument often used to check the alignment of two shafts is the
Dial indicator.
Why must resilient-mount motors have a ground strap?
If the motor were to have a ground (circuit from the hot line to the frame of the motor), the motor frame would be electrically hot w/ out the ground strap. (By rubber)
what is meant by the term rated-load amperage (RLA) as it applies to an compressor motor.
RLA is a mathematical calculation used to get UL approval for a compressor motor.
SFA
Surface factor amperage
FLA
Full-load amperage
RLA
Rated-low amperage
FLA is the current the motor draws while operating at a _________ at the rated voltage.
full-load condition
The alternating current frequency used in the U.S. is
60 cps
CPS
Cycle per second
If the voltage supplied to the motor is well below the motors rated voltage the current draw will be
Higher than it should be.
The current a motor will draw at start-up is known as
Locked rotor amperage.
A sleeve bearing would typically be used in a motor that
Operates with a light load and where noise is a factor.
A bearing used on the bottom of a motor where the shaft is positioned vertically is called a
thrust bearing
Roller bearing are normally used with
Large motors operating with a heavy load.
A direct-drive motor may be connected to the load withe a
Coupling
The width of a drive belt is classified as
“A” or “B” width.
Single-phase motors can be wired to operate on three-phase power.
True or false
True
The approximate FLA for a single-phase, 2 HP motor, operating on 230 V is
12 amps
The approximate FLA for a 3-phase, 5 HP motor, operating at 400 V is
7.6 amps
A motor is rated at 230 V. The upper and lower allowable voltage is
207 V to 253 V.
A loose fitting belt on a belt-driven device will cause
Worn pulley grooves.
A flexible coupling between the drive and driven device corrects
Corrects minor misalignment.
