Preliminary Tests - Grundfos SP Series Installation And Operating Instructions Manual

6.1 Preliminary tests

Test
Supply voltage
Current
Winding resistance
Insulation resistance
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.
• On three-phase units, measure
between the legs (phases).
• By use of an ammeter, set on the
proper scale, measure the current
on each power lead at the control
box or starter. See section
7.6 Electrical data on p. 24 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
drop cable leads in the control box
or starter.
• 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 in section 7.6 Electrical
data on p. 24. Cable resistance
values are in section 7.6.5 Total
resistance of drop cable (OHMS)
on p. 26.
• Turn off power and disconnect
the drop cable leads in the
control box or starter.
• Using an ohm or mega
ohmmeter, set the scale selector
to Rx 100K and zeroadjust 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 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.
If the amp draw exceeds the listed
service factor amps (SFA) or if the
current unbalance 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 shorted.
• 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 drop cable leads are mixed. To
verify lead colors, see resistance
values in section 7.6 Electrical data
on
p. 24.
For ohm values, refer to section
6.1.1 Ohm value chart on p. 14.
Motors of all hp, voltage, phase and
cycle duties have the same value of
insulation resistance.
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