book 2 chapter2 electric
If a motor has 4 poles and is operating at a frequency of 60Hz its synchronous speed is
1,800 RPM
A motor a with a NEMA kVA code letter of of M has a locked-rotor value of
10.0-11.19kVA/hp
Per NEC Section 430.32,a motor with a service factor of 1.0 must trip at
115%of the full load current
The rpm of a 60Hz motor with two poles is
3,600
The electrical energy required to produce 1hp of mechanical energy is
746W
When variable-frequency speed control is used on a motor with a nameplate rating of 480V at 60Hz the voltage-to-frequency ratio is
8
Most industrial motors are NEMA Design
A
Using NEMA frame designations, the distance from the motor feet to the shaft center line is known as the
D dimension
Reconnecting a running motor to act as a generator is known as
Dynamic braking
The NEMA frame designation for gasoline pump motor is
G
The code requiremnts for motor disconnects are coveredin
NEC Articles 430 part IX
The speed of an induction motor depends on the power supply frequency and the
Number of poles
A motor with the field coils connected in parallel with the rotor winding is a
Shunt Motor
In three phase motors, the rotor most commonly used is the
Squirrel cage rotor
To product the motr from overloads and starting failures use a
Thermal protector
A three-phase synchronous motor is started with an
amortisseur winding
The name of the motor part that rotates during operation is the
armature/rotor
To determine the horsepower rating of a motor that is already installed and in place
check the nameplate data
When Studying the operation of electric motors, it is important to remember that magnetic lines of force
do not cross
When using a motor with dynamic braking
electromechanical friction brakes may be required with large loads
The principal reasons for developing the brushless DC motor was to
eliminate commutator problems
A NEMA designation for a type of enclosed motor is
explosion-proof
The letters FLA on a motor name plate stand for
full-load amps
The two primary types of motor of motor enclosures classified by NEMA are
general purpose and guar
The method of braking in which DC is applied to the motor windings after AC is removed is known as
injection braking
Any exposed live parts of motors must be guarded if the motor
operates at 50V or more between terminals
An open AC squirrel cage motor that makes use of form-wound coils and an insulation system is known as an
semi-guarded
When there is a wide variation in both torque and speed requirements, such as a blower or a hoist, use a
series DC motor
The multiplier to the nameplate horsepower rating is called the
service factor
A heating system is most likely to use a
single-phase induction motor
The speed on a multiple winding motor is normally changed by
switching contacts in a motor controls
A type of motor used in precision applications that require constant speed with zero slip is a
synchronous
A delta-connected motor has
the coils connected in parallel
A wye-connected motor has
the coils connected in series
With a constant -torque load , the horsepower
varies in direct proportion to the speed
