Electrical Connection; Motor Protection; Frequency Converter Operation - Grundfos NB Original Installation And Operating Instructions

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 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 connection 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.

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 diagram
inside the terminal box cover.
Warning
Before starting any repair work on motors
incorporating a thermal switch or thermistors, it
must be ensured 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.
Large motor driven via a frequency converter will be loaded by
bearing currents.
Check these operating conditions if the pump is driven via a
frequency converter:
Operating
Action
conditions
2-, 4- and 6-pole
Check that one of the motor bearings is
motors, frame
electrically isolated. Contact Grundfos.
size 280 and up
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.
23