High Voltage Wire Insulation Resistance Test

This section provides information and instruction on high voltage wire insulation resistance test.

Why is Insulation Resistance Testing Required?

All installers and site designers need to perform an Insulation Resistance Test since it is crucial for ensuring the safety, reliability, and longevity of electrical installations. This test helps to:

  • Identify defects: Detect insulation defects, moisture ingress, or physical damage that could lead to failures

  • Prevent failures: Avoid potential short circuits, electrical shocks, and equipment damage

Test Specific Safety Precautions

Follow these safety precautions:

  • Wear appropriate Personal Protective Equipment (PPE): Insulated gloves, safety glasses, and flame resistant clothing

  • Ensure that the circuit is de-energized: Verify that the power is completely turned off and

    locked out

  • Use insulated tools: Ensure that all the tools and the equipment used are rated for the voltage level

  • Follow manufacturer's guidelines: Adhere to the safety recommendations provided by the equipment manufacturer

Example Testing Procedure

Follow these steps:

  1. To prepare for the test, ensure that the wires are disconnected on both sides and that the wires are properly isolated.

  2. To perform the test, use Megger Test equipment, Megaohmeter, or, any other similar equipment.

  3. Test the voltage.

    A common practice is to use a test voltage of 1000 V. Refer to relevant standards such as IEEE 43 or manufacturer specifications for guidance.

  4. Apply the test voltage for one minute.

  5. Record the insulation resistance value at the end of the test duration.

 

Expected Insulation Resistance Value

Compare the measured resistance value against the acceptable limits specified by relevant standards or the wire manufacturer. Generally, higher resistance values indicate better insulation quality. For 600 V to 1000 V rated wires, a minimum insulation resistance of 1 MΩ per kV of operating voltage is often considered acceptable.

Measurements from the AC Set or Stations

Use the following sample table to capture measurements from your test:

AC side measurements

AC Set/Station #

Cable Size

L1 - L2

L2 - L3

L3 - L1

L1 - GNDClosed Ground

L2 - GNDClosed Ground

L3 - GNDClosed Ground

Station 1 AC

 

 

 

 

 

 

 

Station 2 AC

 

 

 

 

 

 

 

Station 3 AC

 

 

 

 

 

 

 

Station 4 AC

 

 

 

 

 

 

 

Measurements from the DC Set or Stations

Use the following sample table to capture measurements from your test:

DC side measurements

DC Set/Station #

Cable Size

1-GNDClosed Ground

2-GNDClosed Ground

3-GNDClosed Ground

4-GNDClosed Ground

DC+/DC-

Station 1 DC

 

 

 

 

 

 

Station 2 DC

 

 

 

 

 

 

Station 3 DC

 

 

 

 

 

 

Station 4 DC