Planning the electrical installation
68
Permanent magnet synchronous motor
Only one permanent magnet motor can be connected to the inverter output.
It is recommended to install a safety switch between a permanent magnet
synchronous motor and the motor cable. The switch is needed to isolate the motor
during any maintenance work on the drive.
Thermal overload and short-circuit protection
The drive protects itself and the input and motor cables against thermal overload
when the cables are dimensioned according to the nominal current of the drive. No
additional thermal protection devices are needed.
WARNING! If the drive is connected to multiple motors, a separate thermal overload
switch or a circuit breaker must be used for protecting each cable and motor. These
devices may require a separate fuse to cut off the short-circuit current.
The drive protects the motor cable and the motor in a short-circuit situation when the
motor cable is dimensioned according to the nominal current of the drive.
Supply (AC line) cable short-circuit protection
Always protect the input cable with fuses. In networks with a short-circuit withstand
of 65 kA or less, standard gG fuses can be used. No fuses need be installed at the
drive input.
If the drive is supplied through busbars, fuses must be installed at the drive input. In
networks with a short-circuit withstand of less than 50 kA, standard gG fuses are
sufficient. If the network has a short-circuit withstand of 50…65 kA, aR fuses are
required.
Size the fuses according to local safety regulations, appropriate input voltage and
the rated current of the drive. Check that the operating time of the fuses is below
0.5 seconds. For fuse ratings, see Technical Data.
WARNING! Circuit breakers are not capable of providing sufficient protection
because they are inherently slower than fuses. Always use fuses with circuit
breakers.
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