Electrical Systems

A compressor’s insulation resistance might be above the manufacturer’s minimum, but what if it has dropped significantly since the previous service?

Would that change your assessment?

A spot insulation-resistance test provides one piece of information. Where recommended by the manufacturer, a polarisation index (PI) test adds another by measuring how insulation resistance changes during a continuous test.

The compressor remains switched off and electrically isolated throughout. The ten minutes refers to the insulation tester running—not the compressor.

The insulation tester applies a steady DC test voltage to the winding insulation:

• After 1 minute, record the insulation resistance.

I get asked a lot what WAGOs are.

They’re basically quick connectors for joining wires without screws.

They’re not the cheapest, but once you use them you won’t go back, especially on service work.

Why I use them:

• Faster than screw terminals

• Solid connection (less chance of loose wires)

• Step 1 — Safety

  • Turn power OFF at isolator or breaker

  • Confirm the motor is not live

Added Electrical Formula Wheel - This may help someone