How to Measure
By means of a voltmeter, which
has been set to the proper scale,
measure the voltage at the control
box or starter. On single-phase units,
measure between line and neutral.
What it Means
When the motor is under load, the
voltage should be within ± 10% of the
nameplate voltage. Larger voltage
variation may cause winding damage.
Large variations in the voltage indicate
a poor electrical supply and the pump
should not be operated until these
variations have been corrected.
If the voltage constantly remains high or
low, the motor should be changed to the
correct supply voltage.
CURRENT
MEASUREMENT
How to Measure
By use of an ammeter, set on the
proper scale, measure the current on
each power lead at the control box.
See page 6, for motor amp draw
information.
Current should be measured when
the pump is operating at a constant
discharge pressure with the motor
fully loaded.
What it Means
If the amp draw exceeds the listed
service factor amps (SFA), check for the
following:
1. Loose terminals in control box or
possible cable defect. Check winding
and insulation resistances.
2. Too high or low supply voltage.
3. Motor windings are shorted.
4. Pump is damaged causing a motor
overload.
WINDING
RESISTANCE
How to Measure
Turn off power and disconnect the
drop cable leads in the control box.
Using an ohmmeter, set the scale
selectors to Rx1 for values under
10 ohms and Rx10 for values over
10 ohms.
Zero-adjust the meter and measure
the resistance between leads.
Record the values. Motor resistance
values can be found on page 6.
What it Means
If all the ohm values are normal, and
the cable colors correct, the windings
are not damaged. If any one ohm value
is less than normal, the motor may be
shorted. If any one 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 drop
cable leads are mixed. To verify lead
colors, see resistance values on page 6.
INSULATION
RESISTANCE
How to Measure
Turn off power and disconnect the
drop cable leads in the control box.
Using an ohm or mega ohmmeter,
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).
What it Means
For ohm values, refer to table below.
Motors of all Hp, voltage, phase and
cycle duties have the same value of
insulation resistance.
SUPPLY
VOLTAGE
OHM VALUE MEGAOHM VALUE CONDITION OF MOTOR AND LEADS
Motor not yet installed:
2,000,000 (or more) 2.0 New Motor.
1,000,000 (or more) 1.0 Used motor which can be reinstalled in the well.
Motor in well (Ohm readings are for drop cable plus motor):
500,000 - 1,000,000 0.5 - 1.0 A motor in reasonably good condition.
20,000 - 500,000 0.02 - 0.5 A motor which may have been damaged by lightning or with damaged
leads. Do not pull the pump for this reason.
10,000 - 20,000 0.01 - 0.02 A motor which definitely has been damaged or with damaged cable.
The pump should be pulled and repairs made to the cable or the motor
replaced. The motor will still operate, but probably not for long.
less than 10,000 0 - 0.01 A motor which has failed or with completely destroyed cable insulation.
The pump must be pulled and the cable repaired or the motor replaced.
The motor will not run in this condition.
TROUBLESHOOTING
10
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