A special end shield with untapped holes for through bolts
in the flange. It is primarily used
for mounting the motor to gearboxes or bulkheads.
They are available in frame sized 143T through 445T.
A current that flows only in one direction in an electric circuit.
It may be continuous or discontinuous and it may be constant or varying.
A motor using either generated or rectified DC power. A DC motor is often used when variable-speed
operation is required.
A definite purpose motor is any motor design listed and offered
in standard ratings with standard operating characteristics but with special
mechanical features for use under service conditions other than usual or for
use on a particular type of application (NEMA).
Some motors can operate on two different voltages, depending
upon how it is built and connected. The
voltages are either multiples of two or the Ö3 of one another.
The relationship between the operating and rest times or repeatable
operation at different loads. A motor
which can continue to operate within the temperature limits of its insulation
system after it has reached normal operating (equilibrium) temperature is considered
to have a continuous duty (CONT.) rating. A motor which never reaches equilibrium temperature
but is permitted to cool down between operations, is operating under intermittent
(INT) duty. Conditions such as a crane
and hoist motor are often rated 15 or 30 minute intermittent duty.
A device which places a load on the motor to accurately measure
its output torque and speed by providing a calibrated dynamic load.
Helpful in testing motors for nameplate information and an effective
device in measuring efficiency.
NEMA has standard motor designs with various torque characteristics
to meet specific requirements posed by different application loads.
The design “B” is the most common design.
NEMA has standard frame sizes and dimensions designating the
height of the shaft, the distance between mounting bolt holes and various other
measurements. Integral AC motor NEMA
sizes run from 143T – 445T, and the center of the shaft height in inches can
be figured by taking the first two digits of the frame number and dividing it
by 4.
Fractional horsepower motors, for which NEMA spells out dimensions, utilize 42, 48 and 56 frames. The shaft height in inches can be established by dividing the frame number by 16
A drip-proof machine with ventilating openings guarded (with
screens) as in a guarded motor.
An open motor in which the ventilating openings are so constructed
that drops of liquid or solid particles falling on it, at any angle not greater
than 15 degrees from the vertical, cannot enter either directly or by striking
and running along a horizontal or inwardly inclined surface.
A dual speed motor with torque values that vary with speed
(as the speed changes the horsepower remains constant).