240v heater

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  #1  
Old 09-08-08, 08:57 AM
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240v heater

quick question,
I ran 12-2 cable from a 20 amp double pole breaker (2-110's) to a dig. programmable T-stat and cable to the heater. I have power into the T-stat, but no display image or power coming out of it. the T-stat is an Aube th115, 240d. it's new.

Is the T-stat toast? how can I test it to determine this?

thanks
 
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Old 09-08-08, 09:08 AM
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Have you used a neon bulb or multimeter to test for voltage on the supply lines at the thermostat box? You should have 120V from each hot to ground and 240V from hot-to-hot.

If voltage tests come out okay, then I would lean toward a defective thermostat.
 
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Old 09-08-08, 09:51 AM
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Looking at the instructions for your tstat, there's really nothing that can go wrong unless:
- you have a defective tstat
- you have the incoming power connected to the LOAD wires (should be connected to the LINE wires)
- your tstat is not making good connection to the baseplate when you snapped it on
 
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Old 09-08-08, 10:28 AM
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I'm not sure about this thermostat in particular, but many of them (especially digital ones) have a battery inside that runs the electronics. Probably a long shot... but worth a check.
 
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Old 09-08-08, 10:59 AM
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from your instructions

 
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Old 09-08-08, 02:18 PM
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I made sure the line and load wires are correct. I'll put a voltmeter on the line wires and see what I'm getting at the end. the breaker is new QOT two switch, double pole, 20amp. my thought is the T-stat is bad, but I'll follow up later.

thanks
 
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Old 09-08-08, 02:44 PM
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That is your problem. The Q0T is not a double-pole breaker, it is a tandem breaker which cannot be used for a 240V circuit. You need to get a double-pole breaker, which is twice the width of a single-pole breaker. Part #Q0220

You can confirm the problem with voltage readings. Measurements will read 120V line-to-ground and 0V line-to-line. A double-pole breaker will measure 240V line-to-line.
 
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Old 09-08-08, 06:21 PM
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This what the QOT2020 look likes



that useally work for 120 volts circuits

but here is the real deal for 240 volts QO220 breaker look like



Merci,Marc
 
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Old 09-09-08, 07:43 AM
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Interesting. I'm getting 120v from both line wires. but yes, 0v from line to line. however, The QO (not QOT) breaker I have shows on the tag either 120v or 240v. salient details on the breaker

Square D QO2020 - QO 20/20A Twin Pole 120/240V Circuit Breaker

why is this? thanks for all the info
 
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Old 09-09-08, 08:08 AM
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The breaker you have can supply 2 120 volt circuits in the space normally taken up by a breaker that would supply 1 circuit.

As others have said you need a QO220, not the QOT2020. They are entirely different animals.
 
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Old 09-09-08, 08:12 AM
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I believe that line in the description means the breaker is for use in 120/240V residential panels as opposed to say 120/208V or 277/480V commercial panels. I agree it could be misleading.
 
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Old 09-09-08, 08:13 AM
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Either your breaker has a bad connection on the buss, or the breaker is bad or the main is out on one leg. The latter can go unnoticed more likely if you had a gas water heater and appliances instead of 240 electric.

If applicable according to what I said, you might want to voltmeter check across the two terminals on the main breaker, to see if 240 there. But -

-[Use caution whenever checking out a main breaker as these are completely different than the other breakers. The wires going into the main breaker stay live, even when turned off!!!! And the amp potential is extremely high, and woud kill in heartbeat if you handled something wrong, whether with hand or tool.]
 
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Old 09-09-08, 08:14 AM
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so if it's a "double pole" tandem breaker, why is it that it won't supply 240v? I understand what's needed at this point, I'm just curious as it's all rather misleading.
 
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Old 09-09-08, 08:17 AM
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Originally Posted by pcboss View Post
As others have said you need a QO220, not the QOT2020. They are entirely different animals.
The poster in his post #9 said he DOES have the QO breaker, and not the QOT breaker. Although, he also has the 2020 tag, along with it. ???
 
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Old 09-09-08, 08:23 AM
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Are your *2* tandem breakers, taken as one unit, the same size as one normal large-size SINGLE breaker?, or twice as big as a normal large-size SINGLE breaker?
 

Last edited by ecman51; 09-09-08 at 08:27 AM. Reason: revised
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Old 09-09-08, 08:54 AM
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The QO2020 is a tandem breaker used as a replacement breaker in older panels. See the difference here form QO catalog:

 
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Old 09-09-08, 09:02 AM
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Originally Posted by Widge View Post
so if it's a "double pole" tandem breaker, why is it that it won't supply 240v? I understand what's needed at this point, I'm just curious as it's all rather misleading.
The breaker is only attached to one of the hot busses in the panel. For 240 volt circuits you need to attach to both the hot busses.

What you have is 2 120 volt breakers in the space of one.
 
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Old 09-09-08, 04:05 PM
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Sometimes for the life of me -

There'd be no confusion if post #9 answered post #8. It be settled.
 
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