3 Wire RTD Sensor| Wiring a 3 Wire RTD | 3 Wire RTD Probe 3 Wire RTD Circuit. In a three-wire circuit two constant current sources are used, in order to compensate for the disadvantages described above for the two-wire circuits. Similar to the two-wire circuit the current source IK2 is used to measure the temperature dependent resistance RT including the lead and terminal contact resistances. Wiring a 3 Wire RTD - Thermometrics Corporation Why Use a 3 Wire RTD? The three wire configuration provides a compensation loop that can be used to subtract the lead wire resistance from the resistance measurement of the element loop, resulting in a value for just the element resistance.