| No. | Codes | Fault Type |
| 1 | 5000 | B: Partial discharges of low energy density or hydrolysis |
| 2 | 5001 | E: Partial discharges of increasing energy density |
| 3 | 5010 | D: Coincidental partial discharges and conductor overheating |
| 4 | 5100 | C: Partial discharges of high energy density, possibly with tracking |
| 5 | 0000 | A: No fault: normal deterioration |
| 6 | 0001 | N: Thermal fault of temperature range 100˚C - 200˚C |
| 7 | 0010 | I: Insulated conductor overheating |
| 8 | 0011 | J: Complex thermal hotspot and conductor overheating |
| 9 | 0100 | F: Low energy discharge: flashover without power follow through |
| 10 | 0101 | K: Coincidental thermal hotspot and low energy discharge |
| 11 | 0110 | G: Low energy discharge: continuous sparking to floating potential |
| 12 | 0120 | H: High energy discharge: arc with power follow through |
| 13 | 0200 | F: Low energy discharge: flashover without power follow through |
| 14 | 0210 | G: Low energy discharge: continuous sparking to floating potential |
| 15 | 0220 | H: High energy discharge: arc with power follow through |
| 16 | 1000 | M: Thermal fault of low temperature range < 150˚C |
| 17 | 1001 | N: Thermal fault of temperature range 100˚C - 200˚C |
| 18 | 1010 | O: Thermal fault of temperature range temperature range 150˚C - 300˚C overheating of copper due to eddy currents |
| 19 | 1020 | P: Thermal fault of high temperature range 300˚C - 700˚C: bad contacts/joints: core and tank circulating currents |
| 20 | 1100 | K: Coincidental thermal hotspot and low energy discharge |
| 21 | 2001 | N: Thermal fault of temperature range 100˚C - 200˚C |
| 22 | 2020 | P: Thermal fault of high temperature range 300˚C - 700˚C: bad contacts/ joints: core and tank circulating currents |