Q: I am testing an old paper-insulated lead cable (PILC) and a modern XLPE cable. Same IR results?
A: No, absolutely not. XLPE and PILC are physically and chemically completely different, and their "healthy" IR ranges differ by several orders of magnitude.
The Material Comparison:
| Feature | XLPE (Cross-linked Polyethylene) | PILC (Paper Insulated Lead Covered) |
| Insulation Type | Synthetic solid polymer (plastic-like) | Paper tape wrapped and saturated with oil |
| Normal IR Range | Extremely high: GΩ to TΩ | Moderate: Tens of MΩ to hundreds of MΩ |
| Moisture Sensitivity | Very low (slow water trees over the years) | Extremely high (instantly drops to 0 Ω on sheath breach) |
| Typical PI Value | Very high: 3.0 to 5.0+ | Lower: 1.5 to 2.0 (rarely exceeds 2.5) |
Junior's Rule: Never apply XLPE standards to PILC, or you will reject good paper cables. Never apply PILC standards to XLPE, as this may energize a critically damaged cable that is about to explode.