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 MECHANICAL
CONSIDERATIONS
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.
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NEMA
DIMENSIONS
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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. |
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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.
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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.
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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.
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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.
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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.
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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.
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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.
|
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ENCLOSURE
TYPES
OF ENCLOSURES
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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.
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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.
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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.
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Totally
enclosed fan enclosed (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.
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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).
|
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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.
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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. |
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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 |
| |
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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. |
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