The Megger Test Record is the structured recording format behind the single most important engineering discipline in flood and moisture-related motor recovery: judging insulation condition by trend, not by one reading. This page is the record itself — usable directly from the browser or printed — plus the reasoning for why each column exists.
Purpose
A single insulation resistance (IR) reading, taken once, tells you almost nothing about whether a motor is recovering or not. This record exists to capture a sequence of readings — baseline through post-drying — so that the trend itself becomes the evidence, following the same discipline built into the flagship Handbook article and referenced by IEEE 43.
When to Use
After any flood, moisture, or condensation exposure, before returning a motor to service
After extended storage or shutdown of an electrical machine
As an acceptance test following a rewind or repair
As part of routine condition-based maintenance on critical motors
Classification
Engineering Discipline
Electrical
Machine Types
Motor, Generator, Transformer
Industries
All — general-purpose
Required Inputs
A megohmmeter appropriate for the machine's rated voltage class
The machine's nameplate data (rated voltage, insulation class) — see IEC 60034 / NEMA MG-1
Confirmed electrical isolation (LOTO complete) before any reading is taken
A thermometer, to record ambient/winding temperature alongside each reading
Expected Outputs
A completed trend table (below) showing IR and calculated Polarization Index (PI = 10-minute reading ÷ 1-minute reading) across each drying/testing stage — the primary input to a recovery-level determination in the Recovery Assessment Worksheet.
The Record
Megger Test Record — IR / PI Trend Log
Date/Time
IR @ 1 min
IR @ 10 min
PI (10min÷1min)
Ambient Temp
Notes
Baseline (as-found)
Before any drying
Day 1
Day 2
Day 3
Compare trend against Acceptance Criteria below
Day 4 (if needed)
Procedure
Confirm electrical isolation and lockout before connecting any test equipment.
Record the baseline reading immediately — even a very low as-found value is useful data, not a result to discard.
Dry the machine per the applicable method for the exposure type.
Re-test at consistent intervals (e.g., daily), recording ambient temperature each time.
Calculate PI at each stage: 10-minute reading ÷ 1-minute reading.
Plot or visually compare the trend across all rows before drawing any conclusion.
Acceptance Criteria
AnalysisA stable or rising IR/PI trend across at least 3 consecutive readings supports proceeding with repair-level recovery. A flat or declining trend — even if one individual reading is numerically "acceptable" — is evidence against it and should trigger further evaluation before re-energizing.
The specific pass/fail numeric threshold is always the machine's own OEM documentation or the applicable standard's guidance — never a generic universal number. This record captures the trend; interpretation still requires engineering judgement.
Engineering Notes
Note
Record ambient temperature every time — insulation resistance is temperature-sensitive, and an uncorrected comparison across different temperatures can make a genuinely improving trend look flat, or vice versa.
Typical Mistakes
Common Mistake
Filling in only the baseline and one "final" reading, skipping the intermediate days — this defeats the entire purpose of the record, since the trend (not the endpoints alone) is the evidence.
Common Mistake
Using a test voltage that doesn't match the machine's rated voltage class. Always confirm against the nameplate first.
