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Old 12-07-2010, 12:22 PM   #1
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Connecting line voltage thermostat


Posted this in HVAC but I'll try here also
I am wiring my shed and have decided to wire my two 1500W/120V radiant heaters to there own circuit with a line voltage thermostat. I was thinking about getting a honeywell CT410B because the price was right ($17 at sears). My question is how to connect the wires? The thermostat says it's 120/240 capable and has 4 wires - 2 black(L1 - T1) and 2 red(L2 - T2) for a positive off rather than just a lowest setting. I want to be able to turn the heat completely off when not in use. Since I am wiring 120 do I connect both line wires to the black from the circuit breaker and both load wires to the black from the heaters and twist the white wires together? Or should i just use 1 of the line and the same color load? or should I connect the black to black and white to red?

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Old 12-07-2010, 03:27 PM   #2
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Connecting line voltage thermostat


Assuming you are using two 120 volt 20 amp circuits, 3000 watts is too much for one 20 amp circuit, L1 and T1 would control one circuit and L2 and T2 would control the other. You only use the thermostat between the hot conductors. Do not switch the neutrals.


Last edited by brric; 12-07-2010 at 03:29 PM.
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Old 12-08-2010, 11:48 AM   #3
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Connecting line voltage thermostat


Thanks, what was I thinking! I am running them on one circuit from a 30 amp breaker with 10/2 wire. But your right I checked the thermostat and it's only rated at 22 amps, 2 1500 watt heaters would be 25 amps, if I did my math correctly. Is there a 30 amp thermostat on the market? Or if I run 10/3 could I put both the black and red on the breaker and use the red for one and the black for the other? The way I'm running them is: C/B --> outlet for heater 1 --> thermostat --> outlet for heater 2 (the heaters have 120 cords on them)
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Old 12-08-2010, 12:11 PM   #4
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Connecting line voltage thermostat


Can you just switch the breaker to a 2 pole to run these at 240 volt? This will cut the amps required in half.
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Old 12-08-2010, 12:15 PM   #5
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Connecting line voltage thermostat


JP or br, could this be run as a MWBC? Does the continuous load rule apply?
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Old 12-08-2010, 12:19 PM   #6
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Connecting line voltage thermostat


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JP or br, could this be run as a MWBC? Does the continuous load rule apply?
Yes it could be. Continuous load rules apply but should not be a factor @1500 watts.
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Old 12-08-2010, 12:31 PM   #7
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Connecting line voltage thermostat


Two 1500 watt heaters at 120 volts is 25 amps times the 1.25 puts it at 31.25 amps so it looks like the 10 awg is even undersized or am I doing this wrong?
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Old 12-08-2010, 12:58 PM   #8
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Connecting line voltage thermostat


A 12-3 MWBC would provide two 120 volt 20 amp circuits capable of providing 1920 watts continuously each.
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Old 12-09-2010, 07:17 AM   #9
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Connecting line voltage thermostat


OK, good schoolin', thanks. So at the risk of sounding cheap I already have enough 10/2 and 12/2 wire so... I could either return my 30 amp breaker for two twenty amp and run 2 12/2 to the thermostat and then one to each heater, or buy a 20 amp double pole breaker and just enough 12/3 to go from the breaker to the thermostat and then run 12/2 to each heater?

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