Variable frequency drive cable sizing

Variable frequency drive power cables between the various system components are the responsibility of the installer and the size and type to be used should be selected to suit the application and on the basis of the continuous current rating of the variable frequency drive and a minimum temperature rating of 70C.

VFD cables sizes should be selected according to local wiring rules using the currents given from the VFD manufacturers. Note that the power terminals of the VFD enclosure and the input/output line reactors are intended for use with cables terminated in crimp lugs with a single hole to match the diameter of the hole or bolt provided.

The VFD provides an electronic type thermal overload function that relies on the measured motor current to estimate the thermal conditions of the motor. For complete motor thermal protection, microtherms or thermistors should be installed in the motor winding and wired to the appropriate trip relay. VFD Extended Features Option provides a thermistor relay function and other features.

Differences in PWM variable frequency drive designs may result in different cable recommendations between manufacturers. In some countries, the recommended cables may not be available. However, the manufacturer's recommendations should be followed as closely as possible. Proper cabling installation of high-performance PWM variable frequency drives will avoid interference with the operation of other plant equipment, as well as ensure proper operation and life of the connected equipment.

Isolating the VFD from the electrical supply must be provided in accordance with your local electrical code. In the event that a second supply is connected to the relay contacts on the control terminal strip (or otherwise brought into the VFD enclosure), suitable marking must be applied to the outside of the VFD enclosure by the installer to indicate the dual supply arrangement in accordance with your local electrical code and other safety requirements. A means of isolating the second electrical supply source will also be required.