What equipment and procedures are required for measuring cable insulation resistance, and what factors can affect test results?

Q: What equipment and procedures are required for measuring cable insulation resistance, and what factors can affect test results?   A: Insulation resistance testing necessitates a megohmmeter (500V/1000V for low/high-voltage cables) applying DC voltage for 60 seconds to measure leakage current. Pre-test steps include disconnecting live conductors, discharging capacitive charge, and cleaning terminals to remove contamination. Key influencing factors: temperature (results double for every 10°C increase), humidity (condensation reduces resistance), cable length (longer cables show lower absolute values), and aging (oxidation/cracking degrades dielectric performance). Acceptance criteria typically require ≥100MΩ for new cables and ≥1MΩ for existing installations, with polarization index (60s/30s reading ratio) >2 indicating good insulation integrity.