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
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.
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.
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.
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 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.
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.
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.
