Preliminary Tests; Total Resistance Of Submersible Drop Cable (Ohms) - Grundfos SP Instrucciones De Instalación Y Funcionamiento

9.1 Preliminary tests

Test
Supply voltage
Current
Winding resistance
Insulation
resistance
18
How to measure
By means of 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).
• By means of an ammeter set to
the proper scale, measure the
current on each power lead at
the control box or starter.
See section 10.7 Electrical data
on page 29 for motor amp draw
information.
• Current should be measured
when the pump is operating at a
constant discharge pressure with
the motor fully loaded.
• Turn off power and disconnect
the submersible drop cable leads
in the control box or starter.
• By means of 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 10.7 Electrical
data on page 29.
Cable resistance values are in
section 10.7.5 Total resistance of
submersible drop cable (ohms)
on page 31.
• Turn off power and disconnect
the submersible drop cable
leads in the control box or
starter.
• By means of 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).
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 power 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.
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 for the
following:
• burnt contacts on motor starter
• 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.
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 motors 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 submersible drop cable leads
are mixed. To verify lead colors,
see resistance values in section
10.7 Electrical data on page 29.
For ohm values, refer to
section
9.1.1 Ohm value chart
page 19.
Motors of all hp, voltage, phase and
cycle duties have the same value of
insulation resistance.
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