Replacing a 4 wire 220V wall heater thermostat.

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Old 08-31-10, 05:16 PM
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Replacing a 4 wire 220V wall heater thermostat.

The old thermostat, an InterTherm TB112, is mounted in a wall receptacle, the heater is across the room, all wiring is inside the walls. The new thermostat is a Honeywell CT410A-B. Both are 2 pole thermostats. I think I have this figured out, but want to make sure I decoded things correctly.

The Honeywell is an integrated unit that has 2 black wires, 1 coming out of L1 and the other out of T1, plus 2 red wires, 1 coming out of L2 and the other out of T2.

The installation diagram shows L1 and L2 going to the power supply with T1 and T2 going to the electric heater. That would mean there would be a black wire (L1) and red wire (L2) going to the power source, and a black (T1) and red (T2) wire going to the heater. Am I correct so far?

The old InterTherm thermostat, consists of 2 individual breakers, each with a red and black wire connected. I am assuming that a black wire from each breaker goes to the power supply, and a red wire from each goes to the heater.

If that is correct, then I should be connecting the Honeywell's black L1 and the red L2 leads to the same power supply feeds going to the InterTherm's black leads. Then connect the Honeywell's black T1 and the red T2 to the wires the InterTherm red wires were connected to, which I assume, go to the heater.

This wire color switch is confusing and disconcerting. I would appreciate having my interpretation of this wiring confirmed.

Also, I have been using a 220V single-pole water-heater timer to shut off the power to one leg of the thermostat at night, thereby stopping the heaters on/off cycles at night.

The Honeywell schematic shows that the L1 - T1 side of thermostat has a thermally activated make/break switch, the other leg has a breaker that trips on a positive off, which I assume shuts off all power to the heater.

A note on the schematic says that the L2 - T2 side leads may be unused. I would assume this means that the L1 T1 side is the controlling side and would be the most logical to break via the timer.

Which leg do you advise as the best one to run through the timer? Or doesn't it make any difference?

Thanks for your help.
 
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Old 08-31-10, 05:58 PM
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I think you are making this more complicated than it really is. First of all, if you have a 2 pole thermostat you have a CT410B, forget the A, the A is a single pole thermostat and only has 2 wires.
http://customer.honeywell.com/techli...0s/67-5169.pdf
I'd forget the colors on the thermostat wires and concentrate on wiring power from your panel to wires L1 and L2 on the thermostat. Then, wire T1 and T2 to the wires going to the heater. You may need a meter to determine which wires are the hot ones from your panel.

As far as your timer, breaking either leg will stop a 240 volt heater, but I don't recommend breaking only 1 leg of a 240 volt heating circuit.
 
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Old 08-31-10, 07:07 PM
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The T-stat will need to break both the hot legs to count as a disconnect means.

The red and black from the panel go the L1 and L2. The leads going out to the heater go to T1 and T2.
 
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Old 08-31-10, 07:14 PM
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OK, the installation pamphlet with this Honeywell thermostat is for both the A & B models (wish they had made that clear). I have the B model - 2 pole.

I was hoping forum wisdom/experience/logic would save me the effort of determining which are the power leads. No such luck. Have meter, will test and then off to L1 - L2 they go. Unfortunately, the hodgepodge inside that wall box would make an experienced electrician flinch. Whites, blacks, reds - all manners of interconnections - makes me hesitant to start this test.

Would appreciate knowing why you don't recommend breaking just one leg of a 220V heater. Seems to work for a water heater - they sell a device specifically for that application. Not wise - why?

Thank you for responding, Joe.
 
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Old 08-31-10, 07:35 PM
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Thanks Boss,

There were several 1 pole 220V thermostats for this application. I chose the 2 pole since that was what the old one was. Guess the single pole would have worked just as well, and it would have only broken one leg of power to the thermostat, leaving one leg live. So why does the thermostat 'NEED' to break both legs, other than to protect the idiot who refuses to turn off ALL power when working on a 220V device like a wall-heater.

Got the connections, just have to find which are the hot ones.
 
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Old 08-31-10, 08:06 PM
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When a disconnect is required for safety it must disconnect bot legs or you still have 120v to ground at the device. Single pole thermostats and timers don't count as safety disconnects but as a way to control the device.
 
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Old 09-01-10, 05:30 PM
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to protect the idiot who refuses to turn off ALL power when working on a 220V device like a wall-heater.
Another way to put it is like this. Most homeowners and many DIYers are not qualified to do any kind of electric work, never ask questions when they are clearly over their heads! This would be a safety to protect them. I commend you for having the common sense to ask.
 

Last edited by pcboss; 09-02-10 at 06:54 AM. Reason: removed comment
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