Grundfos NBG Series - Electrical Connection and Motor Protection; Electrical Connection Safety and Regulations; Motor Protection and Frequency Converters

English (GB)
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10. Electrical connection
The electrical connection must be carried out by a
qualified electrician in accordance with local
regulations.
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 should be carried out as
shown in the wiring diagram inside the terminal box
cover.
10.1 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.
10.2 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.
Check these operating conditions if the pump is
driven via a frequency converter:
Warning
Before removing the terminal box cover
and before removing/dismantling the
pump, make sure that the power supply
has been switched off.
The pump must be connected to an
external mains switch.
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.
Warning
Before starting any repair work on motors
incorporating a thermal switch or
thermistors, make sure that the motor
cannot restart automatically after cooling.
Operating
conditions
Action
2-, 4- and 6-
pole motors,
frame size
280 and larger
Check that one of the motor
bearings is electrically isolated.
Contact Grundfos.
Noise critical
applications
Fit a dU/dt filter between the motor
and the frequency converter
(reduces the voltage peaks and
thus the noise).
Particularly
noise critical
applications
Fit a sinusoidal filter.
Cable length
Fit a cable that meets the
specifications laid down by the
frequency converter supplier. (The
length of the cable between motor
and frequency converter affects
the motor load.)
Supply
voltage up to
500 V
Check that the motor is suitable
for frequency converter operation.
Supply
voltage
between 500
V and 690 V
Fit a dU/dt filter between the motor
and the frequency converter
(reduces the voltage peaks and
thus the noise), or check that the
motor has reinforced insulation.
Supply
voltage of 690
V and higher
Fit a dU/dt filter and check that the
motor has reinforced insulation.