Is your mining application earth leakage relay VFD suitable?

The mining industry is experiencing a growing number of applications of Variable Frequency Drives (VFD) to soft start and control motors driving shovels, draglines, hoists, conveyors, longwalls, mills, fans and pumps.

However, it is often ignored that not all compliant AS2081:2011 earth leakage protection relays are suitable for installations involving VFDs. In AS2081:2011 it states that should a non-linear device be present such as a VFD, frequencies outside of the fundamental 50Hz needs to be taken into consideration when calculating step and touch potential.


Most earth leakage protection relays are designed to detect earth fault current based on the fundamental frequency and therefore have limitations to detect DC, low or high frequency currents which may occur in systems with VFDs under fault conditions (Figure 1).

To ensure that protection of installations incorporating VFDs is adequate, earth leakage protection relays have to accurately detect earth fault currents from DC to a few kHz.




Bender’s RCMA423AS – AC/DC sensitive earth leakage relay

  • Compliant to AS/NZS2081:2011
  • Frequency range: 0…1kHz
  • Response values: 100mA…5A
  • Suitable for installations containing VFD, battery chargers, UPS and converters

See Bender’s safety and protection relay range here.