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Electrical Motors | Questions And Answers
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Electrical Motors | Questions And Answers
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Electrical Motors | Questions And AnswersA 1/10 hp motor is classified as a subfractional-horsepower motor. ✔️
True
A motor operating 5% above rated voltage will run hotter than a motor
operating 5% below rated voltage. ✔️ False
For best full-load efficiency, a motor should be operated at 5 to 10% below
rated voltage. ✔️ False
The starting current of most motors is about twice as large as the running
current. ✔️ False
The rated speed of a motor is the motor's no-load speed. ✔️ False
When operating at rated load, a motor's speed will be about 10% less than
rated value. ✔️ False
Multi-horsepower motors are usually more efficient than are fractional-
horsepower motors when both are operated at rated load. ✔️ True
Explosion-proof motors can allow explosions within the motor enclosure.
✔️ True
Dripproof motors are also known as splashproof motors. ✔️ False
A split-phase motor develops more torque when starting than when running
at rated hp. ✔️ True
It is not practical to reverse the direction of rotation of a split-phase motor.
✔️ False
The capacitors used in capacitor-start motors are designed for intermittent
use only. ✔️ True
, For equal hp motors, the capacitor-start motor draws less locked-rotor
current and provides more starting torque than a split-phase motor. ✔️
True
Direction of rotation in a three-phase motor can be reversed by switching any
two supply lines. ✔️ True
Under the same conditions, single-phase motors are more efficient than three-
phase motors. ✔️ False
The purpose of a motor disconnect switch is to open the supply conductors to
the motor, allowing personnel to work safely on the installation. ✔️ True
The motor overload protection device has the same current rating as the
overcurrent protection device. ✔️ False
External overload protection is recommended for applications in which
ambient temperatures can change drastically. ✔️ False
If one line of a three-phase motor feeder should open, the motor will continue
the run and produce excessive current in the stator circuit. ✔️ True
Most AC motors must not be started on full voltage because the inrush current
will damage the stator windings. ✔️ False
The letters NC, used to describe a contact, stand for No contact. ✔️ False
Compared to AC motors, DC motors require more routing maintenance and
repairs. ✔️ True
Over 90 percent of all motors used run on alternating current. ✔️ True
Compared to an AC motor, the speed of a DC motor is much simpler to control.
✔️ True
A regenerative DC drive can be operated to return power to the system.
✔️ True
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