Schrack Technik GmbH, Wien

Phase Monitoring Relays

Phase Monitoring Relays

Every three-phase system should be monitored by a phase monitoring relay from Schrack Technik. Phase monitoring relays monitor your system and safeguard it against phase sequence, phase failure and asymmetry, the latter with definable asymmetry and an optional neutral conductor.

The most common problem in three-phase system is the possibility that load is distributed unevenly. If one of the phases fails completely, the whole system may be damaged (because a change in phase sequence also reverses the motor). The Series 5 phase monitoring relays from Schrack Technik detect such problems at an early stage and protect the system before any damage occurs.

Phase Sequence Monitoring: As long as all phases are nominal, the relay remains open. If it detects an error, it trips instantly.

Asymmetry Monitoring: If the preset asymmetry level is reached, the relay trips.

Phase Failure Monitoring: If one phase fails completely, the relay closes instantly to avoid serious damage of the system.


  • Phase sequence and phase failure monitoring
  • Detects a broken neutral conductor

Used for:

  • Protection against phase failure:  in thyristor controlled welding machines
  • Phase sequence monitoring
  • Asymmetry monitoring