Electrical Connection; Motor Protection; Frequency Converter Operation; Commissioning And Startup - Grundfos NK Series Installation And Operating Instructions Manual

9. Electrical connection

The electrical connection must be carried out by a qualified
electrician in accordance with local regulations.
Warning
Before removing the terminal box cover and
before removing/dismantling the pump, make
sure that the power supply has been switched off
and that it cannot be accidentally switched on
again.
The pump must be connected to an external
mains switch.
The operating voltage and frequency are stated on the
nameplate. Make sure that the motor is suitable for the power
supply of the installation site.
The electrical connection must be carried out as shown in the
wiring diagram inside the terminal box cover.
Warning
Whenever powered equipment is used in
explosive surroundings, the rules and
regulations generally or specifically imposed by
the relevant responsible authorities or trade
organisations must be observed.

9.1 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 on the back side of the terminal box cover.
Warning
Before starting any repair work on motors
incorporating a thermal switch or thermistors,
make sure that the motor cannot restart
automatically after cooling.

9.2 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.
A large motor driven via a frequency converter will be loaded by
bearing currents.
20
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 an output filter between the motor and
Noise critical
the frequency converter; this reduces the
applications
voltage 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 sinusoidal filter between the motor and
Supply voltage
the frequency converter which reduces the
between 500 V
voltage peaks and thus the noise, or check
and 690 V
that the motor has reinforced insulation.
Supply voltage of Fit a sinusoidal filter and check that the
690 V and higher motor has reinforced insulation.

10. Commissioning and startup

Do not start the pump until it has been filled with
Note
liquid and vented.

10.1 General information

Warning
When pumping drinking water, the pump must be
flushed through with clean water before startup
in order to remove any foreign matters such as
preservatives, test liquid or grease.
10.1.1 Pumps with stuffing box
In the case of pumps with stuffing box, check that the stuffing box
gland is correctly fitted. It must be possible to turn the pump shaft
manually. If the pump has been inactive for a long period, turn it
manually to make sure it has not got stuck. Loosen the stuffing
box or remove the packing.

10.2 Commissioning

10.2.1 Flushing the pipe system
The pump is not designed to pump liquids
containing solid particles such as pipe debris
and welding slag. Before starting up the pump,
the pipe system must be thoroughly cleaned,
Caution
flushed and filled with clean water.
The warranty does not cover any damage caused
by flushing the pipe system by means of the
pump.