Grundfos SP Installation And Operating Instructions Manual page 26

1. Supply voltage
Measure the voltage between the phases by
means of a voltmeter.
On single-phase motors, measure between
phase and neutral or between two phases,
depending on the type of supply. Connect the
voltmeter to the terminals in the motor-
protective circuit breaker.
1
2
3
2. Current
consumption
Measure the amps of each phase while the
pump is operating at a constant outlet head (if
possible, at the performance where the motor
is most heavily loaded). For maximum
operating current, see nameplate.
Items 3 and 4: Measurement is not necessary when the supply voltage and the current consumption are normal.
3. Winding resistance
Disconnect the submersible drop cable from
the motor-protective circuit breaker. Measure
the winding resistance between the
conductors of the drop cable.
4. Insulation
resistance
Disconnect the submersible drop cable from
the motor-protective circuit breaker. Measure
the insulation resistance from each phase to
earth (frame). Make sure that the earth
connection was made carefully.
Related information
6. Electrical connection
26
The voltage must, when the motor is loaded, be within the range
specified in section Electrical connection
The motor may burn if there are larger variations in voltage. Large
variations in voltage indicate poor power supply, and the pump must
be stopped until the defect has been remedied.
On three-phase motors, the difference between the current in the
phase with the highest consumption and the current in the phase with
the lowest consumption must not exceed 5 %. If so, or if the current
exceeds the rated current, there are the following possible faults:
• The contacts of the motor-protective circuit breaker are burnt.
Replace the contacts or the control box for single-phase
operation.
• Poor connection in conductors, possibly in the cable joint. See
item 3.
• Too high or too low supply voltage. See item 1.
• The motor windings are short-circuited or partly disjointed. See
item 3.
• Damaged pump is causing the motor to be overloaded. Pull out
the pump for overhaul.
• The resistance value of the motor windings deviates too much
(three-phase). Move the phases in phase order to a more uniform
load. If this does not help, see item 3.
For three-phase motors, the deviation between the highest and the
lowest value must not exceed 10 %. If the deviation is higher, pull out
the pump. Measure motor, motor cable and drop cable separately,
and repair or replace defective parts.
Note: The operating winding of single-phase 3-wire motors will
assume the lowest resistance value.
If the insulation resistance is less than 0.5 MΩ, the pump must be
pulled out for motor or cable repair.
Local regulations may specify other values for the insulation
resistance.
.