What is insulation deterioration?
Insulation that is slowly losing its ability to hold current in — cracking, hardening, tracking and falling resistance — and how an inspector decides how far it has gone.
Insulation deterioration means the insulation around the conductors is losing its insulating quality over time. It shows as cracked, brittle or hardened sheaths, soft or swollen material, browning from heat, tracking marks on connector and transformer surfaces, cuts and abrasion, or insulation resistance that falls from one test to the next.
Deterioration is progressive and can be hidden: leakage current to earth grows until it becomes an earth fault, which can trip the CCR's protection and take out lights. Early signs with steady, acceptable insulation resistance are recorded and trended. Visible deterioration or a falling trend is repaired or replaced and re-tested. Insulation resistance below the allowed limit, exposed conductor, tracking or an earth fault is critical and made safe first.
What the inspector sees on the surface: cracks, hardening, browning, tracking. It can be present while the insulation resistance reading is still acceptable.
A measurement of how well the insulation holds back current. A low reading can appear with nothing visible, so it is read alongside the visual check and the trend.
- Make the area safe. Work under the permit-to-work. Isolate, lock off and prove dead before touching or testing.
- Record as found. Photographs of the surface condition, with date and location, before cleaning or handling.
- Inspect the insulation. Cracks, hardening, softening, swelling, browning, tracking, cuts, exposed conductor.
- Test insulation resistance. Use the method and test voltage in the procedure, and discharge the circuit afterwards as it requires.
- Compare with the trend. Read the result against the limit and the previous readings, not on its own.
- Classify and act. Minor, major or critical, then record, repair or replace and re-test, or make safe, and fix the cause such as heat or water.
Frequently Asked Questions
Q1What does insulation deterioration mean in AGL inspection?
A gradual loss of the insulating quality of cable sheaths, joints, connector mouldings, transformer windings and lead wires. It shows as cracking, hardening, softening, swelling, discolouration or tracking, or as insulation resistance that falls over time. It is recorded, classified by how far it has gone and what it affects, and acted on according to the site's procedures.
Q2Why does insulation matter in a series circuit?
The insulation keeps the circuit current inside the conductors. When it deteriorates, current can leak to earth, which shows up as falling insulation resistance and then as earth faults. An earth fault can trip the CCR's protection and take out lights, and exposed or leaking insulation is a shock hazard.
Q3What causes insulation to deteriorate?
Age, heat from overload or a loose connection, moisture and water ingress, sunlight, fuel, oil and de-icing chemicals, mechanical stress and abrasion, rodent damage, and electrical stress such as overvoltage. Finding the cause matters, or the replacement insulation fails the same way.
Q4What does deteriorated insulation look like?
Cracked, brittle or hardened sheaths, soft or swollen insulation, browning or other discolouration from heat, tracking marks on connector or transformer surfaces, cuts and abrasion, and exposed conductor. It can also look sound and still read low on test, which is why inspection and testing are used together.
Q5How is insulation deterioration classified?
By how far it has gone and what it affects. Minor means early signs with insulation resistance still acceptable and steady, which is recorded and trended. Major means visible deterioration or a falling trend, so repair or replacement is planned and the asset is re-tested. Critical means insulation resistance below the allowed limit, exposed conductor, tracking or an earth fault, and it is isolated and made safe first. The limits and exact grading come from the manufacturer, the project specification and the site's inspection procedure.
Q6How is insulation resistance different from a visual check?
A visual check sees the surface condition. An insulation resistance test measures how well the insulation holds back current, with the circuit isolated and the procedure followed. A good reading does not clear insulation that is visibly cracked, and a poor reading can appear with nothing visible, so each result is read alongside the other and the trend over time.
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