Pump Motors
21
Level 2
A.O.Smith
FAILURE TO START
(MOTOR HUMS OR ATTEMPTS TO START)
■
Check voltage at motor line terminals. If
voltage is inadequate to start motor, check for
loose connections, undersized wiring, over-
loaded circuit or other causes of voltage drop.
■
Start switch contacts not closed when motor
is not operating. Switch may require adjust-
ment. Switch contacts dirty or pitted.
■
Capacitor (where used) is “shorted” or “open”.
■
Check motor windings for “open” or “short”.
■
Check for continuity through protector.
■
Turn the motor shaft by hand to get the “feel”
of the motor. If the shaft feels tight or
doesn’t turn smoothly:
•
Check the bearings for smooth operation.
•
See if there is evidence of the rotor
striking the stator.
•
Check for internal corrosion, cracked end
frames, clogged fan or other obstruction
within the motor.
•
Check pump for obstructions, binding
impeller, or bent shaft.
OVERHEATING
As in all motor applications, excess heat is very
detrimental to motor operation and life. Heat
over time breaks down motor insulation and
leads to failure. The relationship of temperature
to life is geometric. In other words, as the tem-
perature goes up the winding life is shortened at
an increasing rate.
A continuously running pump motor may be
hot to the touch and this by itself does not mean
the motor is overheating.
Excess heat has many possible causes:
■
Low voltage. The voltage may be low at the
source or there may be excessive voltage drop
when the load is applied due to too small a
wire size.
