What is it
Measurement with megohmmeter to verify dielectric integrity between conductors and to ground.
Why is it done
Reduces risks of ground faults and nuisance trips; detects moisture, contamination, and insulation aging.
How is it done
- Instrument: megohmmeter (250/500/1000 VDC; HV equipment may require 2.5–5 kV).
- Safety: LOTO, discharge before and after, disconnection of sensitive loads, and verification of absence of voltage.
- Connection: positive to conductor under test, negative to return/ground or another conductor.
- Readings: record IR1 (1 min) and optional IR10 for PI=IR10/IR1 or DAR=IR30s/IR60s.
- Corrections: note temperature and apply correction factors when necessary; document with photos.
Expected results
- High values (MΩ/GΩ) with PI ≥ 2 typically indicate healthy insulation.
- Low or decreasing values suggest moisture/contamination or dielectric deterioration; consider drying/rehabilitation.