IEC 60345: Insulation Resistance Under Humid Conditions — Environmental Humidity Effects on Insulation

Why Tropical Regions Have Higher Electrical Failure Rates — Humidity Effects on Insulation

IEC 60345:1971 specifies insulation resistance measurement under humid conditions. Polar insulating materials (phenolic, nylon) at 95% RH adsorb just a few molecular layers of water, and surface resistivity can drop from 10¹⁴ Ω to 10⁸ Ω — six orders of magnitude. This explains why tropical/subtropical regions have significantly higher electrical equipment insulation failure rates.

TNLab — Humidity is insulation most “gentle” but most persistent killer — it will not cause immediate breakdown, but will slowly degrade insulation resistance over months.