9.2 Preliminary tests
Test
How to measure
What it means
Supply voltage
1
2
3
TM001371
With a voltmeter set to the proper scale, measure the
voltage at the control box or starter.
On single-phase units, measure between line and
neutral.
On three-phase units, measure between the legs
(phases).
When the motor is under load, the voltage must be
within ± 10 % of the value stated on the
nameplate. Larger voltage variation may cause
winding damage.
Large variations in the voltage indicate a poor power
supply and the pump must not be operated until
these variations are corrected. If the voltage
constantly remains high or low, the motor must be
changed to the correct supply voltage.
Current
TM001372
With an ampmeter set to the proper scale, measure
the current on each power lead at the control box or
starter. See section for motor amp draw information.
Current must be measured when the pump is
operating at a constant outlet pressure with the motor
fully loaded.
If the amp draw exceeds the listed service factor
amps (SFA), or if the current imbalance is greater
than 5 % between each leg on three-phase units,
check the following:
•
Burnt contacts on motor-protective circuit breaker.
•
Loose terminals in starter or control box or
possible cable defect. Check winding and
insulation resistances.
•
Supply voltage too high or low.
•
Motor windings are shortened.
•
Pump is damaged, causing a motor overload.
Winding resistance
TM050028_051
1
Turn off power and disconnect the submersible drop
cable leads in the control box or starter.
With an ohmmeter, set the scale selectors to Rx1 for
values under 10 ohms and Rx10 for values over 10
ohms.
Zero-adjust the ohmmeter and measure the
resistance between leads. Record the values.
Motor resistance values can be found in
section Insulation resistance and ohm value chart.
Cable resistance values are in section Insulation
resistance and ohm value chart.
If all the ohm values are normal, and the cable colors
correct, the windings are not damaged.
If the ohm value is less than normal, the motors may
be shorted.
If the ohm value is greater than normal, there is a
poor cable connection or joint. The windings or cable
may also be open.
If some of the ohm values are greater than normal
and some less, the submersible drop cable leads are
mixed. To verify lead colors, see resistance values in
section Insulation resistance and ohm value chart.
Insulation resistance
TM050029_051
1
Turn off power and disconnect the submersible drop
cable leads in the control box or starter.
With an ohmmeter or megohmmeter, set the scale
selector to Rx 100K and zero adjust the meter.
Measure the resistance between the lead and ground
(discharge pipe or well casing, if steel).
For ohm values, refer to section Insulation resistance
and ohm value chart..
Motors of all hp, voltage, phase and cycle duties have
the same value of insulation resistance.
25
English (US)
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