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240V stat

I was thinking one leg was +120 and the other leg was -120. This gives the 240-volt potential difference. Checking either leg to ground should read 120 volts. I'm guessing there is a DPST relay behind terminals 3&4 and the stat controls the relay coil. There are a number of different ways to wire this. What's behind the terminal strip? Here is one of many ways to wire this A/C circuit.


  • Paul Rohrs_4
    Paul Rohrs_4 Member Posts: 466

    does a 240V (ac) line feeding this floor heating stat not need a neutral? Both 120V hot lines feed terminals 1 & 2 from the 240V, but I can just wire-nut off the White Common? This stat is feeding two electric infloor radiant heat cables and it is wired correctly, I am just curious about the neutral on the 240V.

    (Power then feeds from terminal 3 to the load and 4 is the neutral.)



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  • Empire_2
    Empire_2 Member Posts: 2,343

    What is the actual in floor radiant load,...120, or 240vac? Looks like there are 2 loads being energised off the t-stat. If your load is 240 both lines are 120 vac and it does need a ground wire (there is no common) in case a short develops.

    Often times there is a double pole break if 240, to kill the power to the elements so that no voltage at all is present when the circuit is off. This would eliminate any partial heating if a short occurs in the elements itself. It is for safety and fire hazard. If your element shorts half way, the 120 to ground would still try to power the circuit to ground, increasing your amp draw and possibly causing a fire or insulation melt. Also it would help if you had more info on the set up of this control. From what I see It could be 120 or 240 vac. WHere are you thinking of using a wire nut? at the stat, on the board?

    Mike T.
  • carol_3
    carol_3 Member Posts: 397

    One of the strange things in life is that 240V doesn't have a neutral. That's because 240V is alternating current, and alternating current alternates. Picture a sine wave here. :) As one side is high (240V), the other side is low (0 volts, or neutral) It's all about the "potential" difference between the two.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Each leg alternates between +120 and -120 in direct opposition to the other.

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