Checking Motor And Cable; Spe - Grundfos SP Series Installation And Operating Instructions Manual

12. Checking motor and cable

DANGER
Electric shock
Death or serious personal injury
- Switch off the power supply before starting any
work on the product.
- Make sure that the power supply cannot be
accidentally switched on.
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.
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.
18

12.1 SPE

The following is only valid for SPE pump sets.
DANGER
Electric shock
Death or serious personal injury
- Make sure that motor cables ends are not live
before starting work on the product.
- Make sure that the power supply cannot be
accidentally switched on.
In case of unintended flow of water through a non-energized
pump there is a risk that the moving parts of the pump and the
motor will start rotating, thereby generating voltage over the
terminals. The size of the voltage depends on the speed of
rotation. Due to this the motor terminals must be considered as
live until proven otherwise.
The voltage must, when the motor is loaded, be within the range
specified in section 6. Electrical
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.
connection.