| S.No. | Field / Checkpoint | Reference | Status |
|---|---|---|---|
| A. CIRCUIT IDENTIFICATION | |||
| A1 | Circuit no. + location + cable size + length Acceptance: Per drawing | Per cable schedule | OK NC NA |
| A2 | Test date + tester (megger model + voltage) Acceptance: Per voltage class | Megger 500V / 1000V / 2500V | OK NC NA |
| B. TEST PROCEDURE + RESULTS | |||
| B1 | Insulation resistance phase-to-phase (R-Y, Y-B, R-B) Acceptance: Per code | ≥ 1 MΩ per IS 732 | OK NC NA |
| B2 | Insulation resistance phase-to-earth (each phase) Acceptance: Per code | ≥ 1 MΩ | OK NC NA |
| B3 | Reading at 1 minute + 10 minute (Polarisation Index PI = 10min/1min) Acceptance: Computed | PI ≥ 2 indicates good | OK NC NA |
| C. ACCEPTANCE | |||
| C1 | Pass / Fail per circuit Acceptance: Logged | Below 1 MΩ → reject + investigate | OK NC NA |
| C2 | Annual re-test for fixed wiring (LV) / 5-yearly for industrial Acceptance: Year tested | Per maintenance schedule | OK NC NA |
Insulation Resistance (IR) Test verifies that the insulation between electrical conductors + earth is adequate — preventing short circuits, electrical fires, and personal shock. For every cable, every motor winding, every electrical panel installed on-site, IR must be tested before commissioning + recorded.
Governing standards: IS 732:2019 (Code of Practice for Electrical Wiring Installations), IS 3043:2018 (Code of Practice for Earthing), CEA Regulations 2010. Without an IR Test Register, electrical compliance is unverifiable; statutory electrical inspector cannot approve installation.
Equipment: 500V or 1000V or 2500V DC megger (Megohmmeter); higher test voltage for higher rated cables.
Test conditions: - Apply test voltage between live conductor + earth - Hold for minimum 60 seconds - Record resistance value in megohms (MΩ) - Test between phase-to-phase + phase-to-neutral + each phase-to-earth
Acceptance criteria (per IS 732): - LV cables (≤ 1.1 kV): ≥ 1 MΩ per kV of voltage; minimum 1 MΩ - MV cables (3.3-33 kV): ≥ 100 MΩ-km (megohms × km of cable length) - HV cables (66 kV+): ≥ 1000 MΩ-km - Motor windings (newly installed): ≥ 100 MΩ - Switchboards / panel boards: ≥ 100 MΩ each circuit
Test frequency: - Pre-commissioning: 100% of installation; mandatory - Annual maintenance: rolling per equipment - Post-fault: when fault occurred; verify integrity post-repair - Post-modification: after any wiring change
Documentation: equipment ID + location, test voltage, IR value, ambient temperature (affects readings), date, tester signature, equipment calibration ref.
1. Test voltage wrong — using 500V megger on 11kV cable; reading meaningless. Match megger voltage to cable rating. 2. No temperature compensation — IR varies with temperature (higher temp = lower resistance). Specify ambient + apply correction factor. 3. Test not held long enough — short test (5-10s) reads transient + lower than actual; minimum 60s required. 4. Equipment energised during test — dangerous + invalid results. Isolate + earth before testing. 5. No baseline / trend — annual readings without baseline don't reveal gradual degradation. 6. Connection corrosion — bad megger probe contact gives high reading (apparent good insulation); verify probe. 7. Damaged cable not retested after repair — repair completed; IR test missed. 8. No statutory inspector certification — large installations need Electrical Inspector approval; without IR Register, inspector won't certify.
Companion formats: - Earthing Test Register (FMT-MEP-009) — earthing resistance verification - MEP cable schedule (BOQ + installation tracking) - Statutory electrical inspector approval certificates
Codes + standards: - IS 732:2019 — Code of practice for electrical wiring installations - IS 3043:2018 — Code of practice for earthing - IS 7098 (Parts 1-4) — XLPE cables for various voltages - IS 1554 (Parts 1-2) — PVC insulated cables - IS 13947 series — Low voltage switchgear - CEA (Measures Relating to Safety + Electric Supply) Regulations 2010 - NEC 2023 — National Electrical Code India