Circuit & test conditions
Rule note
Test voltage is recorded on the test record only. Use the same voltage and the same test duration for every test you want to trend, and never exceed the cable’s rated test voltage (check the manufacturer data; 600 V and 5 kV cables differ). Insulation resistance falls as the cable warms.
Rule note
Set the minimum from your project specification or the applicable standard. 50 is a placeholder, not an acceptance limit. A reading below the outlier limit’s share of the median is flagged.
Optional. Gives MΩ·km for comparing different lengths.
Readings
One row per measurement. An AGL series circuit cable is normally single-core, so test conductor to earth and use one row per circuit or per section; conductor-to-conductor rows apply only to multi-core cable. The 10-minute reading is optional and only needed for the polarization index. If the megger shows over-range, enter its maximum reading and treat the result as “greater than”.
| Measurement | 1-min (MΩ) | 10-min (MΩ) | At 20 °C (MΩ) | PI | Status |
|---|
Trend vs previous tests
Enter earlier results for the same circuit and the same measurement, taken at the same test voltage and already corrected to 20 °C. The current result is the lowest corrected reading from the Calculate tab. A steady fall between tests is an early warning even when each reading still passes. A slow decline of roughly 10 to 20% a year is commonly treated as normal ageing, so judge each step against the time between tests.
| Test date | IR at 20 °C (MΩ) | Change vs previous | Status |
|---|
Test record
A summary of the latest analysis for filing. It updates as you type. Use Print to print it or save it as a PDF from your browser.
How the readings are analysed
1. Reading analysis
PI = R(10 min) / R(1 min): below 1 = poor · 1 to 2 = questionable · above 2 = good
Flag: reading below the outlier limit × median of all readings
2. Trend
Flag: fall of more than 25% between tests (watch) or 50% (action). These are planning thresholds, not standard limits. A slow decline of roughly 10 to 20% a year is commonly treated as normal ageing, so judge each step against the time between tests.
Engineering note
Engineering note: The halving rule for temperature and the polarization index bands follow common insulation-testing practice (IEEE Std 43 covers rotating machines) and are applied here as general guidance for cable. Where the cable manufacturer gives a temperature correction table, use that instead. The polarization index is less meaningful when the 1-minute reading is very high. Take acceptance limits from your project specification or the applicable standard (for maintenance testing see FAA AC 150/5340-26 and ICAO Airport Services Manual, Doc 9137, Part 9). Disconnect the circuit from the CCR and any monitoring equipment, discharge the cable before and after every test, and follow your lock-out and safety procedure. This tool is for planning and record keeping and does not replace the project specification; see the Legal Notice.