As far as I know, IEC has not mentioned medium voltage in any of its standards except in IEC 61000-3-6.
The following table provides the different voltage levels as per IEC 61000-3-6.
| Voltage Level | Range (line-to-line) | |
|---|---|---|
| LV (Low voltage) | Un ≤ 1kV | |
| MV (Medium voltage) | 1kV < Un ≤ 35kV | |
| HV (High voltage) | 35kV < Un ≤ 230kV | |
| EHV (Extra high voltage) | Un > 230kV | |
NOTE The boundaries between the various voltage levels may be different for different countries
It is good to note that [1] is the only IEC standard that mentions about Medium voltage. All other IEC standards consider voltages above 1kV to be high voltage.
References:
- IEC/TR 61000-3-6
Electromagnetic compatibility (EMC) – Part 3-6: Limits – Assessment of emission limits for the connection of distorting installations to MV, HV and EHV power systems