PACMotion VFD Input/Output Chokes Installation Guide Section 3
GFK-3185A August 2020
Output Line Chokes 5
Section 3: Output Line Chokes
3.1 Using Output Chokes
AC Inverters use a fast switching pulse width modulation (PWM) technique to create a variable
frequency AC Output to the connected motor. The fast switching of the output of the drive when
connected with long motor cables results in a reflected voltage at the motor which can be up to three
times the AC supply voltage, with a very fast rise time. Output chokes help to reduce this peak voltage,
and increase the rise time, to reduce the stress applied to the motor insulation and prevent damage.
Output chokes are recommended whenever any of the following conditions are met:
• The connected motor is not known to be suitable for use with a PWM output Inverter (as
confirmed with the motor manufacturer)
• The motor cable length exceeds the maximum permissible motor cable length stated for the
product in the relevant user manual
o Specified cable lengths apply to standard type copper shielded cable only
o For unshielded cables, the maximum length may increase by 50%
o Using a choke allows the maximum cable length to increase by 100%
• High capacitance motor cable is used, e.g. typically fire-resistant cables
3.2 Dimensions – Open Type
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