Grundfos NK Montage- Und Betriebsanleitung Seite 30

8. Electrical connection
The electrical connections should be carried out by an authorized
electrician in accordance with local regulations.
Warning
Before removing the terminal box cover and
before any removal/dismantling of the pump,
make sure that the power supply has been
switched off.
The pump must be connected to an external
mains switch.
The operating voltage and frequency are marked on the
nameplate. Make sure that the motor is suitable for the power
supply of the installation site.
The electrical connections should be carried out as shown in the
wiring diagram inside the terminal box cover.
Warning
Whenever powered equipment is being used in
explosive surroundings, the rules and
regulations generally or specifically imposed by
the relevant responsible authorities or trade
organisations must be observed.
8.1 Motor protection
Three-phase motors must be connected to a motor-protective
circuit breaker.
All three-phase Grundfos MG and MMG motors of 3 kW and up
incorporate a thermistor. See the instructions in the motor
terminal box.
Carry out the electrical connection as shown in the wiring
diagram in the terminal box cover.
Warning
Whenever motors incorporating a thermal switch
or thermistors are to be repaired, make sure,
before starting to work, that the motors cannot
start automatically after cooling.
8.2 Frequency converter operation
All three-phase motors can be connected to a frequency
converter.
Frequency converter operation will often expose the motor
insulation system to a heavier load and cause the motor to be
more noisy than usual due to eddy currents caused by voltage
peaks.
Large motors driven via a frequency converter will be loaded by
bearing currents.
30
Check these operating conditions if the pump is driven via a
frequency converter:
Operating
Action
conditions
2-, 4- and 6-pole
motors, frame Check that one of the motor bearings is
size 225 and electrically isolated. Contact Grundfos.
larger
Fit a dU/dt filter between the motor and the
Noise critical
frequency converter (reduces the voltage
applications
peaks and thus the noise).
Particularly noise
critical Fit a sinusoidal filter.
applications
Fit a cable that meets the specifications laid
down by the frequency converter supplier.
Cable length
(The length of the cable between motor and
frequency converter affects the motor load.)
Supply voltage up Check that the motor is suitable for
to 500 V frequency converter operation.
Fit a dU/dt filter between the motor and
Supply voltage
frequency converter (reduces the voltage
between 500 V
peaks and thus the noise), or check that the
and 690 V
motor has reinforced insulation.
Supply voltage of Fit a dU/dt filter and check that the motor
690 V and higher has reinforced insulation.