Thermostat Wiring Question


  #1  
Old 08-12-08, 08:03 AM
J
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Thermostat Wiring Question

Thanks for taking my question. I am trying to replace an old, ugly baseboard thermostat with a new one (Honeywell CT410B). I have minimal experience in wiring, but I think I can do it with a little advice. I gently pulled the old thermostat out but left all wiring intact and connected.
FYI, the old thermostat has three connection points...1) the top has one black...this is the input and 2) the bottom black...the output and 3) the bottom...the white. I know the top connection is the input because it is always reading 240V regardless of the thermostat setting. And the bottom is the output because it only reads 240V when the heat is turned on.
The new thermostat has four connections…1) top black 2) top red 3) bottom black 4) bottom red.
Now on to what’s behind the old thermostat in the electrical box…There are two wires coming in the recessed box from the top and one wire from the bottom. The two that are coming in from the top are connected to one another (both black wires connected together and both white wires are connected together). I connected my multimeter to these top wires at their connection point and it was 240V. Last, there is one lone black wire that is connected the two previously joined black wires...this is the one that is going to the old thermostat (input on top). Ok, now on to the bottom of the box. The wire exiting the bottom of the recessed box contains just two wires...the black is connected to the thermostat on the black side and the white wire is connected to the other group of white wires previously mentioned. This whole group of white wires are connected to the thermostat via a single white wire.
All the above makes sense to me, hopefully I’ve described it enough. Ideas on how to begin? What is the red on the new thermostat? I have a picture for details, I will e-mail it if needed.
Here is what I was going to do...I figured I’d ask first.
1) the two black wires coming from the top...they were going to go to the top of the new thermostat on the black side.
2) the two white wires coming from the top...they were going to go to the top of the new thermostat on the red side.
3) the black wire exiting the bottom...it was going to go to the bottom of the new thermostat on the black side.
4) the white wire exiting the bottom…it was going to go to the bottom of the new thermostat on the red side. Note: this was previously connected to the two other white wires coming in from the top, then connected to the only white connection on the old thermostat.
Ideas? Thanks in advance.
John
 

Last edited by jrharts; 08-12-08 at 08:18 AM. Reason: Deleted link to picture...
  #2  
Old 08-13-08, 03:23 PM
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From your description it sounds like you have a 240 volt heater controlled by a t-stat that is only controlling one side of the circuit. You could replace this with a 240 volt 2 pole t-stat.

The junction box you described sound like power in and power out to another part of the circuit. do you have multiple baseboard heaters? They may not be in the same room.

In a 240 volt circuit using only 2 wire cable plus ground the white is actually a 120 volt hot leg. Code now requires that it be re-identified as a hot conductor by coloring it a color besides white, gray or green. This is commonly done with black or red tape or a magic marker.
 
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Old 08-14-08, 06:36 AM
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Thermostat Wiring Question

Thanks for your reply.

I think you are right...there is another small baseboard heater in a different room fed by the additional wires in the box.

So do I connect black on black (thermostat) and white in on red (thermostat)?

Thanks again for your help--I really appreciate it.

John
 
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Old 08-14-08, 06:51 AM
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I reread your proposed connections in Post #1 and agree that that is how the connections should be made.

Your T-stat may be labelled Line and Load. Load would be the pair of wires leading down to the unit. Line would be the power from the panel and continuing on to the other heater.
 
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Old 08-14-08, 07:06 AM
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Thermostat Wiring Question

Thanks! I'll give it a try tonight...

They are labeled L1 (line) and T1 (load...to heater)...just like you said!
 
  #6  
Old 08-15-08, 08:02 AM
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Thermostat Wiring Question

pcboss,

Thanks for your help--everything worked great with the install. I really appreciate you help.

John
 
  #7  
Old 08-15-08, 08:09 AM
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You are welcome. Glad to hear that your problem is resolved.
 
 

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