The Onset T-MAG-SPT-300 Potential Voltage Transformer Sensor, 300 VAC is used with the FlexSmart TRMS Module to provide accurate measurement of AC voltage. One or two PTs can be used with each FlexSmart TRMS module. This sensor offers an accuracy of ±1% (from 10% to 130% of rated voltage). Because these transformers tie directly into the line, they should only be used by qualified personnel.