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4. Fuses blow or circuit
breakers or overload
relays trip
a) Tank is too small. Check voltage at starter panel and motor.
If voltage varies more than - 10 %/+ 10 %,
contact power company. Check wire sizing.
b) Motor overload protection set too low. Cycle pump and measure amperage.
Increase size of overload protection or adjust
trip setting to maximum motor nameplate (full
load) current.
c) Three-phased current is imbalanced. Check current draw on each lead to the motor.
Must be within - 5 %/+ 5 %. If not, check motor
and wiring. Rotating all leads may eliminate this
problem.
d) Motor short-circuited or grounded. Turn off power and disconnect wiring.
Measure the lead-to-lead resistance with an
ohmmeter (RX-1). Measure lead-to-ground
values with an ohmmeter (RX-100K) or a
megaohmmeter. Record values. If an open or
grounded winding is found, remove the motor,
repair and/or replace.
e) Wiring or connections are faulty. Check proper wiring and loose terminals.
Tighten loose terminals. Replace damaged
wires.
f) Pump is blocked or seized. Turn off power and manually rotate pump shaft.
If shaft does not rotate easily, check coupling
setting and adjust as necessary. If shaft rotation
is still tight, remove pump and inspect.
Disassemble and repair the pump.
g) Defective capacitor (single-phase motors). Turn off power and discharge capacitor.
Check with ohmmeter (RX-100K). When the
meter is connected to the capacitor, the needle
should jump towards 0 ohms and slowly drift
back to infinity ( ∞ ). Replace capacitor if
defective.
h) Motor overload protection devices at higher
ambient temperature than motor.
Use a thermometer to check the ambient
temperature near overload protection devices
and motor. Record these values. If ambient
temperature at motor is lower than at overload
protection devices, especially where
temperature at overload protection devices is
above 104 °F (40 °C), replace standard
protection devices with ambient-compensated
protection devices.
Problem Possible cause Remedy
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