NEMA
Frame/Shaft Sizes
Frame
numbers are not intended to indicate electrical characteristics
such as horsepower. However, as a frame number becomes
higher so in general does the physical size of the motor
and the horsepower. There are many motors of the same
horsepower built in different frames. NEMA (National
Electrical Manufacturers Association) frame size refers
to mounting only and has no direct bearing on the motor
body diameter.
By NEMA definition,
two-digit frame numbers are fractional frames even though
1 HP or larger motors may be built in them. Three-digit
frame numbers are by definition integral frames. The
third numeral indicates the distance between the holes
parallel to the base. It has no significance in a footless
motor. Refer to NEMA Standard Dimension Chart.
NEMA Suffixes
C
= NEMA C face mounting (specify with or without rigid
base)
D = NEMA D flange mounting (specify
with or without rigid base)
H = Indicates a frame with rigid base
having an F dimension larger than that of the same frame
without the suffix H. For example, combination of 56H
base motors have mounting holes for NEMA 56 and NEMA
143-5T and a standard NEMA 56 shaft.
J = NEMA C face, threaded shaft pump
motor
JM = Close-coupled pump motor with
specific dimensions and bearings
JP = Closed-coupled pump motor with
specific dimensions and bearings
M = 6 3/4" flange (oil burner)
N = 7 1/4" flange (oil burner)
T, TS = Integral horsepower NEMA standard
shaft dimensions if no additional letters follow the
"T" or "TS."
TS = Motor with NEMA standard "short
shaft" for belt driven loads
Y = Non-NEMA standard mount; a drawing
is required to be sure of dimensions. Can indicate a
special base, face or flange.
Z = Non-NEMA standard shaft; a drawing
is required to be sure of dimensions.
NEMA Prefixes
Letters
or numbers appearing in front of the NEMA frame number
are those of the manufacturer. They have no NEMA frame
significance. For example, the letter in front of LEESON's
frame number, L56, indicates the overall length of the
motor.
Mounting
Unless
specified otherwise, motors can be mounted in any position
or any angle. However, unless a drip cover is used for
shaft-up or shaft-down applications, drip-proof motors
must be mounted in the horizontal or sidewall position
to meet the enclosure definition. Mount motors securely
to the mounting base of equipment or to a rigid, flat
surface, preferably metallic.
Types of
Mounts
Rigid
base
Is bolted, welded or cast on main frame and
allows motor to be rigidly mounted on equipment.
Resilient base
Has isolation or resilient rings between motor
mounting hubs and base to absorb vibration and noise.
A conductor is imbedded in the ring to complete the
circuit for grounding purposes.
NEMA C face mount
Is a machined face with a pilot on the shaft
end which allows direct mounting with a pump or other
direct coupled equipment. Bolts pass through mounted
part to threaded hole in the motor face.
NEMA D flange mount
Is a machined flange with rabbet for mountings.
Bolts pass through motor flange to a threaded hole in
the mounted part. NEMA D flange kits are stocked by
some manufacturers, including LEESON.
Type M or N mount
Has special flange for direct attachment to
fuel atomizing pump on an oil burner. In recent years,
this type of mounting has become widely used on auger
drives in poultry feeders.
Extended through-bolt
Have bolts protruding from the front or rear
of the motor by which the driven load is mounted. This
is usually used in applications involving small direct
drive fans or blowers.
Enclosure
Types of Enclosures
Drip-proof
Vents in endshield and/or frame are to prevent
drops of liquid from falling into motor within a 15
degree angle from vertical. Designed for use in areas
that are reasonably dry, clean, and well ventilated
(usually indoors). If installed outdoors, it is recommended
that the motor be protected with a cover that does not
restrict the flow of air to the motor.
Totally enclosed air over (TEAO)
Dust-tight fan and blower duty motors designed
for shaft mounted fans or belt driven fans. The motor
must be mounted within the airflow of the fan.
Totally enclosed non-ventilated (TENV)
No vent openings, tightly enclosed to prevent
the free exchange of air, but not airtight. Has no external
cooling fan and relies on convection for cooling. Suitable
for use where exposed to dirt or dampness, but not very
moist or hazardous (explosive) locations.
Totally enclosed fan cooled (TEFC)
Same as TENV except has external fan as an
integral part of the motor, to provide cooling by blowing
air around the outside frame of the motor.
Totally enclosed, hostile and severe environment
motors
Designed for use in extremely moist or chemical
environments, but not for hazardous locations.
Totally
enclosed blower cooled motors
Same as TEFC except external fan must run on
a power supply that is independent of the inverter output.
Cooling per MG 1.6 (IC 46).
Explosion-proof motors
Have bolts protruding from the front or rear
of the motor by which the driven load is mounted. This
is usually used in applications involving small direct
drive fans or blowers.
CLASS I
(Gases, Vapors)
Group A Acetylene
Group B Butadiene, ethylene oxide,
hydrogen, propylene oxide
Group C Acetaldehyde, cyclopropane,
diethel ether, ethylene, isoprene
Group D Acetone, acrylonitrite, ammonia,
benzene, butane, ethylene dichloride, gasoline, hexane,
methane, methanol, naphtha, propane, propylene, styrene,
toluene, vinyl acetate, vinyl chloride, xylene.
CLASS II (Combustible Dusts)
Group E Aluminum, magnesium and other
metal dusts with similar characteristics.
Group F Carbon black, coke or coal
dust
Group G Flour, starch or grain dust
The motor ambient temperature is not to exceed +400C
or -250C unless the motor nameplate specifically permits
another value, and is noted on the nameplate and in
the literature. LEESON explosion-proof motors are approved
for all classes noted except Class I, Groups A &
B.
NOTE:
All above data is for reference purposes only
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