The Rated Voltage Factor of Potential Transformers is the maximum limit of excess voltage up to which the voltage transformer can maintain its rated characteristics. It is mentioned in percentage of the nominal voltage.
For instance a Rated voltage factor of 1.2 would mean that the Potential Transformer can maintain its rated characteristics up to 120% of the nominal voltage.
| Rated voltage factor | Rated time | Primary Winding Connection |
| 1.2 | Continuous | Between phases in a network Between transformer star-point and the earth in any system |
| 1.2 1.5 | Continuous for 30 seconds | Between the phase and earth in a system whose neutral is effectively earthed |
| 1.2 1.9 | Continuous for 30 seconds | Between the phase and earth in a system whose neutral is non-effectively earthed with automatic fault tripping |
| 1.2 1.9 | Continuous for 8 hours | Between the phase and earth in a system whose neutral is isolated without automatic fault tripping or in a system with resonant earthing without automatic fault tripping |