Checking Of Motor And Cable - Grundfos MS Serie Instrucciones De Instalación Y Funcionamiento

10. Checking of motor and cable

1. Supply voltage
2. Current
consumption
Items 3 and 4: Measurement is not necessary when the supply voltage and the current consumption are
normal.
3. Winding
resistance
20
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.
Measure the amps of each
phase while the pump is
operating at a constant
discharge head (if possible,
at the capacity where the
motor is most heavily loaded).
For maximum operating
current, see nameplate.
Disconnect the submersible
drop cable from the motor-
protective circuit breaker.
Measure the winding
resistance between the leads
of the drop cable.
When the motor is loaded, the voltage should be
within the range specified in section
The motor may burn if there are larger variations in
voltage. Large variations in voltage indicate poor
power supply, and the motor 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, the following
faults are possible:
• The contacts of the motor-protective circuit
breaker have burnt.
– Replace the contacts or the control box for
single-phase operation.
• Poor connection in leads, possibly in the cable
joint.
– See item 3.
• Too high or too low mains 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 assembly for overhaul.
• The resistance value of the motor windings
deviates too much (three-phase operation).
– Move the phases in phase order to a more
uniform load. If this does not help, see item 3.
Three-phase motors: The deviation between the
highest and lowest value must not exceed 10 %.
If the deviation is higher, pull out the pump
assembly. Measure motor, motor cable and drop
cable separately, and repair/replace defective
parts.
Note: On single-phase, 3-wire motors, the
operating winding will assume the lowest
resistance value.
5.1 General.