Unipolar or Bipolar Thermostat: Understanding Polarity and Wiring

This article explains the difference between unipolar (2-wire) thermostats, which cut a single conductor and remain energized, and bipolar (4-wire) thermostats, which cut both conductors, completely interrupting the power supply. Unipolar thermostats do not require specific polarity, while bipolar thermostats require adherence to LINE and LOAD polarity for safe installation.

Understanding wire polarity is essential for properly installing a thermostat and ensuring the safe operation of your heating system.

Single-pole thermostats (2 wires)

Single-pole thermostats interrupt the current on only one conductor of the power supply line.

This means:

  • The thermostat and heating devices remain energized at all times, even when the heating is not running.

  • Only one side of the power supply is interrupted when the system is off.

Baseboard thermostats in the TH1120, TH1121, TH1123, TH1124, TH1143, and TH1144 series are equipped with two non-polarized wires.

In summary: the wiring direction does not matter.

Installation on a four-wire circuit

It is possible to install a single-pole thermostat on a four-wire setup.

In this case, simply:

  • Connect the second line (L2 / N) together using an appropriate connector.

Double-pole thermostats (4 wires)

Double-pole thermostats interrupt both conductors of the power supply line.

This means:

  • When the thermostat is not calling for heat, power to the heating devices is completely interrupted.

Thermostats in the TH1500 series are equipped with four polarized wires:

  • The power supply wires are located at the outer ends and identified as LINE.
  • The wires intended for the heating device are located in the center and identified as LOAD.

⚠️ It is important to respect the indicated polarity (LINE and LOAD) during installation.

Product models associated with this article:

  • (Wi-Fi) TH1123WF, TH1124WF, TH1143WF, TH1144WF, TH1500WF
  • (Zigbee) TH1123ZB, TH1124ZB, TH1500ZB
  • (Others) TH1120RF, TH1121RF, TH1500RF, TH1120P, TH1120, TH1124NP

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