Pump Motors
11
Level 2
A.O.Smith
Service
Factor
SERVICE FACTOR
Typical service factors for full rated one horse-
power pool pump motors are 1.65 for square
flange and 1.4 for NEMA C. One horsepower jet
pump motors typically have a 1.4 service factor.
Over the years, various amp ratings have been
used on motor nameplates. Some motors may
have rated amps which are amps at one horse-
power. This number is basically useless since
the impeller loads the motor to the service fac-
tor. This motor would also have a rating for full
load, service factor or max amps. This is the fig-
ure to use when checking a replacement motor
after installation. Some service people make a
temporary connection so that the amps may be
easily checked, or the connections are made so
that a loop in the wire is available for checking
amps.
If total horsepower or horsepower times ser-
vice factor is difficult for service persons to
understand, the concept is practically impossible
to explain to a homeowner. If a one horsepower
motor came off the installation, a one horsepow-
er must go back on. Uprated motors are ones on
which the horsepower is increased and the ser-
vice factor is decreased. The total horsepower
remains the same. To see how this works, make
a copy of a motor manufacturers full rated and
uprated motor listings. Put the two listings side
by side so that the one horsepower uprated
motor lines up with the three quarter horsepow-
er full rated motor. You will see that the charac-
teristics such as amps and weight are the same.
The same comparison may be done with pump
curves.
