Product Manual

Insulation Class
Insulation systems are rated by standard NEMA classifications accord-
ing to maximum allowable operating temperatures. They are as follows:
Class Maximum Allowed Temperature*
A 105°C (221°F)
B 130°C (266°F)
F 155°C (311°F)
H 180°C (356°F)
* Motor temperature rise plus maximum ambient
Generally, replace a motor with one having an equal or higher insulation
class. Replacement with one of lower temperature rating could result in
premature failure of the motor. Each 10°C rise above these ratings can
reduce the motor’s service life by one half.
Service Factor
The service factor (SF) is a measure of continuous overload capacity at
which a motor can operate without overload or damage, provided the
other design parameters such as rated voltage, frequency and ambient
temperature are within norms. Example: a 3/4 HP motor with a 1.15 SF
can operate at .86 HP, (.75 HP x 1.15 = .862 HP) without overheating
or otherwise damaging the motor if rated voltage and frequency are
supplied at the motor’s leads. Some motors, including most LEESON
motors, have higher service factors than the NEMA standard.
It is not uncommon for the original equipment manufacturer (OEM)
to load the motor to its maximum load capability (service factor). For
this reason, do not replace a motor with one of the same nameplate
horsepower but with a lower service factor. Always make certain that
the replacement motor has a maximum HP rating (rated HP x SF) equal
to or higher than that which it replaces. Multiply the horsepower by the
service factor for maximum potential loading.
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