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Discussion Starter #1 (Edited)
Remodelling a bedroom and want to install a better looking thermostat for baseboard heater.

Happened to have a new one - Honeywell CT410A. Single pole line voltage thermostat. It has just two terminals Line in and line out. Like this:







Took the old one out. It is a Federal Pacific Electric of Canada model 27-111. Sticker says "SINGLE LINE BREAK" :-




Existing wiring had Black to 1 and 3. And a single White to 2. Like this:





Checking on bench:

- On old thermostat, connections 2 and 4 are connected together so tsta has no effect. Presumably just a pass through?

- 1 and 3 are switched by the thermostat.

- There is about 115kohm resistance between 2/4 and 3 when tstat is off and vs both 1/3 when on.

One other piece of info - panel breaker and wiring feeds this thermostat/heater as well as a second tstat and heater in an adjoining room.

The baseboard heaters are only used to back up a central heat pump system and are normally turned totally down.

Finally questions!
1. Is there any reason that they connected the single white wire to terminal 2?
2. Can I just connect the two blacks to the new tstat. Does it matter which one is load and which one line? Just cap the white wire?
3. Is there any reason I should not use the new tstat?
 

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Having never seen that configuration, I can only offer a guess.

But I think you're correct. My interpretation is that you can connect line in from the breaker box, both hot and neutral, to 1 and 2 (respectively.) Then you could connect 3 and 4 (hot and neutral, respectively) from there to the heater itself.

Of course, if your power comes in to the heater, then you'd only need two wires, 1 and 2, from the hot wire in to the heater, back to the hot terminal on the heater.

So why is that white wire on #2? Where does it come from? It certainly doesn't seem to be doing anything for the heater.

My only guess would be if the thermostat had a backlight, or some programmable functionality, and it needed power for those functions. The new one doesn't, so you don't need it.
 

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Connect the two black wires (1&3)to your new stat. Cap the white.

If there is another white that was possibly connected to 4 then join the two whites with a nut.
 

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Discussion Starter #4
Connect the two black wires (1&3)to your new stat. Cap the white.

If there is another white that was possibly connected to 4 then join the two whites with a nut.

Thanks for confirming that! No other white pigtail. But whites from panel, to room heater and to bathroom heater do join at wire nut. White pigtail came from same wirenut.



I was just puzzled as to why someone had gone to some trouble to add a pigtail from where other whites joined in box, out to tstat. Been like that for the 46 years we have lived here!
 
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