Motor Disconnect Detection

Motor Disconnect Detection

Today’s Fun Fact Friday is about disconnects located between variable speed drives (VSDs) and motors. For safety reasons, these disconnects are installed when the VSD is not within the eyesight of the driven equipment. Let’s talk about how this should be wired, what is often done wrong today, and a better solution available on the ABB 580 series.

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The traditional/proper solution has an aux contact on the motor disconnect, wired in its own conduit back to the VSD, disabling the VSD when opened.

What constitutes a bad installation? No aux contact, or an aux contact’s control wiring sharing a conduit with motor wires.

Tech Note 45 goes into detail on what happens if there is no aux contact, but the short version is that the VSD trips out on Over Current from motor inrush current.

While I appreciate the traditional aux contact solution, I like innovation that reduces cost and increases reliability. The Motor Disconnect Detection feature eliminates the need for an aux contact. This standard feature on the ACH580 senses when a disconnect switch is opened and automatically adjusts its output.

As a result, the VSD does not trip offline once the disconnect is closed, instead ramping the motor up to setpoint. Tech Note 45 has info on the only (1) parameter setup.

Also standard in ACQ580 and ACS580.

A conduit (cable canal) is required for installations in North America. Moreover, the bypass option for drives is also available only in this region.

  • ACH580 drives family
  • ACQ580 drives family
  • ACS580 drives family


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