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Electrical Wiring

4-wire thermostat but only 2 wires

12 years ago

All HD had for a 240 V thermostat was a 4-wire Honeywell CT410B. My baseboard heater is apparently wired with power to the heater and a switching wire to the thermostat. I hooked up black to L1 on the tstat and the white to T1. Now the heater is on all the time. What SHOULD I have done. For those of you with protective instincts, yes, I always turn off the breaker when working on wiring.

Thanks

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Comments (8)

petey_racer
12 years ago
You SHOULD have gotten the correct thermostat for the application. Just 'cause HD doesn't have it does not mean it doesn't exist.
Get the proper thermostat from an electrical or plumbing supply house, industrial supply (Grainger, McMaster-Carr, etc), online, etc.
bus_driver
12 years ago
That thermostat should work fine for your situation. One advantage of that one over the single pole is that the CT 410B has a real OFF position. Perhaps you connected it wrong. Why the need to replace the thermostat? Was it heating all the time previously?
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The big reason to use solid vs stranded wire is that solid wire is easier to thread into those terminals. With stranded wire, there can be a problem if a loose strand manages to contact an ajacent terminal. More likely because the terminals in a thermostat are so close together. Just had a problem with our thermostat. It started running 2 degrees past set temperature. (I have it set for a 2 degree temp differential because the heater was constantly kicking on, running for just a bit and then kicking off...which was driving me nutz.) After a bit of sleuthing, I found that the caulking backer rod that I had shoved under an exterior door (across the room from the thermostat) had become unwedged and there was a significant draft from underneath the door. (The backer rod was supposed to be a temporary fix that I did a couple of winters ago but forgot all about it...) Once I got that hole plugged up (with a better temporary fix), the thermostat quit heating past set temp. I don't know for sure if the draft was the reason the thermostat got weird or if it was a coincidence.... Whatever, I did buy a new thermostat to replace the old one but haven't installed it since the problem seems to be resolved. Just tossing my recent experience out there as a potential cause because a new therm hasn't fixed your problem. (Yes, I know my thermostat is in a poor location and should be moved away from drafts from opening/ closing exterior doors. Just no good or easy place to relocate it to and it's a low priority problem.)
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Ron Natalie
12 years ago
I disagree with Petey (and with Bus). There is nothing wrong with the thermostat in this application. 410A would have been a better fit but all you're doing is leaving out the second pole on the 410B.

You've wired it wrong, though for the life of me I can't think of how you did it. If you'd hooked up the wrong terminals it would be OFF all the time. I suspect you've somehow shorted the wires together separate from the thermostat itself.

The color of the wiring isn't particularly obvious. I got it wrong myself (my dumb fault for not reading the instructions).

There's not much to this device, the operation is purely mechanical which closes the two switches.
brickeyee
12 years ago
There is no reason to switch both legs of a 240 V load exepct at a disconnect.

The hazard for something like a heater that ay have exposed elements (even if they are out of touch range) is that only switching one side leaves the heating element with 120 V on it.

If anything touches the heating element is is electrically hot, even though it is not producing any heat.
yosemitebill
12 years ago
I think you may have connected the wiring to the L2/T2 side.

According to the Honeywell datasheet, L1/T1 is thermostatically switched AND also breaks when turned to the off position. L2/T2 is NOT thermostatically switched and ONLY breaks when turned to the off position.

If wired on the L2/T2 side only, the heat would always be on unless the control was turned to the off position.
Ron Natalie
12 years ago
Thanks Bill, there ya go.
petey_racer
12 years ago
yosemitebill is right on. That is the reason I said what I said. Both poles of a 2-pole t-stat are not the same.

Rather than have a DIY try and figure out which is which I simply suggested using the correct one.
HU-177562966
5 years ago
Hello guys, I stumbled on this site from bouncing around the net for a solution. I am in the same boat as Pete-racer. My garage heater from Dr.Heater has an internal thermostat with power already wired to the thermostat. The heater has an option to bypass the internal tstat and use a wall stat by connection two wires between the 2. My problem is that the tstat I want to use from Cadet is a double pole with 4 wires - 2 Load (red/black) and 2 Line (red/black). The Cadet has a display and I guess requires some power. So my question is (u probably already figured it out): how do I attach the 2 cables from the heater to the 4 from Cadet?

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