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Isolator switch


Also called a disconnect switch or disconnector, this component is essentially a substation “off” switch. It isolates the substation from the utility feed and is used for other applications. The isolator installed in air applications can be seen in the open (off) position with a visible gap that ensures a physical distance between the contact points. You’re likely already familiar with the isolator switch because it’s an integral part of the lockout/tagout (LOTO) procedure. 


Isolators come in many different shapes and sizes. They can be manually operated, or motor operated locally, remotely, or automatically. Isolators can be standalone components, or they can be coupled directly to other components, such as circuit breakers or grounding switches.


Failure modes

  • Insulation breakdown (due to voltage spikes, long-term overvoltage or lightning strikes)

  • Operating mechanism wear/malfunction and misalignment

  • Insulator wear/malfunction (supports the isolator switch)

  • Contact wear or fused contacts


Reliability considerations

  • Mechanical and electrical test of operating mechanism

  • Alignment checks

  • IR scanning for insulators

  • Partial discharge (PD) measurements

  • Visual inspection

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