I have a question about an old federal pacific baseboard heater thermostat's wiring. I disconnected this thermostat 2 weeks ago, thinking that we were going to remove the heater. Now we've decided to keep the heater, and I don't remember how the thermostat was wired. The therm box has two lines in it: one in, one out. Each line has 1 black, one white, and one bare ground. I have attached a pic of the back of the thermostat. It only has 3 places to connect. Poles 2, 3, and 4. Can anyone help me out and tell me what hooks to each pole?

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  • Wait, terminal 1 is missing? Is this a 120V heater, not 240V?
    – Ecnerwal
    Sep 17, 2019 at 18:04
  • I would agree on not connecting backwards, but one of the line terminals looks unused. It was common to only break 1 side of a 240v heater in years past. Then one of the lines would directly connect to one of the loads., tried posting this to your answer but it would not let me
    – Ed Beal
    Sep 17, 2019 at 18:08
  • All 3 terminals appear to have been hooked up. I can see a small scratch or indent under each screw.
    – Roadie
    Sep 17, 2019 at 18:19
  • I just added another pic. There are 2 heaters on this line. Each have their own thermostat. This is a very crude diagram of the first heater's thermostat wiring.
    – Roadie
    Sep 17, 2019 at 18:37
  • Maybe that will help give an idea of what the guy was doing when he installed these?
    – Roadie
    Sep 17, 2019 at 18:39

1 Answer 1


This is 240V split-phase, so both hots are equivalent. The white wire should be remarked one of the 8 legal hot colors, since it is not a neutral. If I were wiring this in conduit, with the choice of any of 8 colors, I would use black and black because the hots are interchangeable; no need to distinguish hots from each other.

This thermostat is single pole. They make a double-pole version where terminal 1 is populated, that one connects 1-3 and also 2-4. This one simply leaves in terminal 3 as a convenient splice block, it connects to no other terminal ever.

Pick one wire from each cable; join them (I don't care how as long as it's code legal; feel free to use terminal 3 as a splice block).

Of the two remaining wires, put one on each of the terminals 1 and 3.

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