Electric Thermostats


Old 01-02-06, 04:14 PM
Thread Starter
Join Date: Jan 2006
Posts: 1
Question Electric Thermostats

I'm replacing the old thermostat to our baseboard heater. How do I determine which line is the 'load' wire and which is the 'line' wire ? I thought I could just connect red to red, black to black, etc.
There are 4 wires (2 red and 2 black) in the box. On the back of the old thermostat there were only two (red and black) wires. The old wiring had the 2 red wires from the box wire-nutted together and the two black wires connected to the red and black wires (1 on each) of the thermostat.
Can anyone help ?
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Old 01-02-06, 04:24 PM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Your old thermostat was a 120 volt thermostat. Your new one is a 240 volt thermostat. As you see, you can use a 120 volt model in some 240 volt applications, however it is not recommended.

In your setup one red wire and one black wire are load wires, and one black and one red wire are line wires. The two line wires are hot, the two load wires are not except when the thermostat decides that heat is necessary. If the wires come from two different cables or conduit then the two load wires will come from the same cable or conduit, as will the two line wires. If they all come from the same conduit then it could be wither pair.

With the four wires exposed and separated, use a two wire tester to test for voltage on the wires. The two with voltage are the line wires, the two without voltage are the load wires. You can use the two wire tester between two wires or between one wire and the ground. You can also use an analog multimeter and look for 240 volts between two wires.

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