Insulation resistance testing is performed on both Class I and Class II appliances during a PAT test.
What Is Insulation Resistance?
The insulation on electrical wires prevents live conductors from touching each other or the appliance casing. Over time, insulation degrades due to heat, moisture, mechanical damage, or age.
How Is It Tested?
The PAT tester applies a test voltage (typically 500V DC) between the live and neutral conductors and the earth. The resulting resistance is measured in megohms. A reading below the minimum threshold indicates insulation breakdown.
What Causes Insulation Failure?
- Age and general wear
- Heat damage from overloading
- Moisture ingress
- Mechanical damage to cables
- Chemical exposure
Why It Matters
Insulation breakdown is invisible. An appliance can look fine outside while having dangerously degraded insulation inside. Only electronic testing catches this.
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