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Old 01-11-2012, 03:51 PM   #1
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Questions about wiring a line voltage thermostat


[x-posted from HVAC - sorry for the duplicate post. Doc Holliday suggested I post in this forum as well]

Hello DIYers,

I am attempting to replace a line voltage thermostat for my electric baseboard heater. I had a few questions, please bear with me:
The old thermostat has screw terminals where the wires attached (photo #1), but the new thermostat (photo #2) has wires directly attached. How should I attach these wires to the wires in the wall - wire nuts?
The old thermostat had a green grounding screw, but I don't see any such thing in the new thermostat (photo #2). Where does the ground wire from the wall need to go?
I am not sure how the wires match up. In the wall, there are 2 sets of wires - each set has 1 white and 1 black. In the new thermostat, there are 2 sets of wires - but each set has 1 red and 1 black. Does black go to black and red go to white?
There is some green corrosion and some blackening on a few of the wires in the wall. Could this be from moisture? Is the wire still OK to use?
It's hard to see in the photos, but the plastic electrical box in the wall is broken - a piece of the plastic broke off from the main one. Do I need to put a new box in?

Thank you so much - sorry for all the questions, you guys are always so helpful!

// Joe
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Old 01-11-2012, 03:53 PM   #2
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Questions about wiring a line voltage thermostat


line to RED
load to BLACK

Done

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Old 01-11-2012, 04:05 PM   #3
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Questions about wiring a line voltage thermostat


The new thermostat is plastic so it doesn't require a ground.
Look in the instructions and verify which wires are line and which are load.
Does the thermostat have an OFF on the dial?
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Old 01-11-2012, 04:50 PM   #4
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Questions about wiring a line voltage thermostat


The wires have become too hot because of the faulty thermo or loose lug screws. Cut them back to where they are in good condition. Someone for the box question and you are good to go.

Nice meter BTW.

Last edited by zappa; 01-11-2012 at 04:53 PM.
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Old 01-11-2012, 05:17 PM   #5
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Questions about wiring a line voltage thermostat


That box is both old, and broken. Since it appears to be mounted in an easily combustible surface, and from the look of those wires you've already come close to having some unanticipated combustion, I'd go ahead and replace the box. That box also kinda looks like it might have been too small for that many wires to begin with. You can cut/break out the old box, and install a remodel box in its place. You may have to slightly enlarge the wall opening.
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Old 01-11-2012, 05:27 PM   #6
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Questions about wiring a line voltage thermostat


The line wires are labeled L1 and L2 on the T-stat.
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Old 01-11-2012, 05:36 PM   #7
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Questions about wiring a line voltage thermostat


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The line wires are labeled L1 and L2 on the T-stat.
Whoa, good catch.
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Old 01-11-2012, 05:38 PM   #8
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Questions about wiring a line voltage thermostat


Looking at the picture it looks like black is one contact and the red is another contact. L1 is line and T1 is load(heater).
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Old 01-11-2012, 05:42 PM   #9
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Questions about wiring a line voltage thermostat


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Originally Posted by joed View Post
Looking at the picture it looks like black is one contact and the red is another contact. L1 is line and T1 is load(heater).
Thanks for the confirmation.
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Old 01-11-2012, 08:20 PM   #10
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Questions about wiring a line voltage thermostat


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Originally Posted by a7ecorsair View Post
The new thermostat is plastic so it doesn't require a ground.
Look in the instructions and verify which wires are line and which are load.
Does the thermostat have an OFF on the dial?
Yes, it has an OFF position.
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Old 01-11-2012, 08:20 PM   #11
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Questions about wiring a line voltage thermostat


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Originally Posted by joed View Post
Looking at the picture it looks like black is one contact and the red is another contact. L1 is line and T1 is load(heater).
Which wire goes to which line wire on the thermostat? Do I match the black wire to the black wire and white to red? Don't want to hook it up backwards
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Old 01-11-2012, 09:31 PM   #12
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Questions about wiring a line voltage thermostat


I would put the whites to the red air and the black to the black pair.
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Old 01-11-2012, 10:41 PM   #13
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As long as the pairs are correct to line and load it does not matter.
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Old 01-12-2012, 03:07 AM   #14
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Questions about wiring a line voltage thermostat


Interesting. There appears to be no consistent standard for the color coding of terminals on 2-pole thermostats these days. The last person who asked here (a couple weeks ago) I foolishly advised that the red pair would be one pole and the black pair the other pole. It was the only way that made sense to me. That resulted in a dead short! Each pole had one red and one black. This thermostat, on the other hand, is wired exactly as I had assumed. I guess the bottom line is that one must read the manual or use a meter to be sure.
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Old 01-12-2012, 07:48 AM   #15
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Questions about wiring a line voltage thermostat


Quote:
Originally Posted by thinksincode View Post
Yes, it has an OFF position.
Since it has an OFF, that means both sides of the T-stat interrupt a power leg. If you don't have the manual and the wiring isn't labeled you will need a meter to check the two connections through the t-stat.
I just took another look at the picture and I clearly see L1 and T1 marked on the base. I'd guess the other side will say L2 and T2.
The L1 and L2 go to the supply power and T1 and T2 to the load.


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