Reference / IR Temperature Correction
Quick reference · Grade G
IR Temperature Correction
Insulation resistance falls roughly exponentially as temperature rises. Readings taken at different temperatures are only comparable after correcting them to one reference temperature.
Multiplier to reference temperature θ = 10 °C
| Test temperature | to 20 °C | to 40 °C |
|---|---|---|
| 0 °C | 0.250 | 0.063 |
| 5 °C | 0.354 | 0.088 |
| 10 °C | 0.500 | 0.125 |
| 15 °C | 0.707 | 0.177 |
| 20 °C | 1.000 | 0.250 |
| 25 °C | 1.414 | 0.354 |
| 30 °C | 2.000 | 0.500 |
| 35 °C | 2.828 | 0.707 |
| 40 °C | 4.000 | 1.000 |
| 45 °C | 5.657 | 1.414 |
| 50 °C | 8.000 | 2.000 |
| 55 °C | 11.314 | 2.828 |
| 60 °C | 16.000 | 4.000 |
| 65 °C | 22.627 | 5.657 |
| 70 °C | 32.000 | 8.000 |
| 75 °C | 45.255 | 11.314 |
Example
A cable reads 800 MΩ at 30 °C. Corrected to 20 °C with θ = 10 °C: 800 × 2^((30 − 20)/10) = 1600 MΩ. The same insulation measured on a colder day would read higher; correcting both readings to 20 °C makes the trend meaningful.
Exponential approximation of insulation resistance versus temperature. IEEE Std 43 and NETA MTS/ATS are cited as pointers only; their tables are not reproduced. © RokBench.