Heating wiring size

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Old 08-01-04, 01:32 PM
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Heating wiring size

The existing fan heater in my garage is a wall recessed unit located in the middle of the opposite wall of the 2 garage doors and has never kept the garage warm. I want to replace it with 2 baseboard heaters which will be located adjacent to each door and thus distribute the heat evenly and quieter. The existing fan heater is 4000 watts / 220V and connected to a 30A breaker with about 15 feet of #10/2 heater cable and there is nothing else on this circuit. The new 2 baseboard heaters will be 1500 watts / 220V each (no space for longer ones).

Due to my layout and available access, I plan to install a new junction box (JB-A) where the existing heater is to get the power and from there go to my new wall thermostat with about 25 feet of #12/2 heater cable and after to another junction box (JB-B) with about 10 feet of #12/2 heater cable. From JB-B one cable will feed one baseboard with about 20 feet of #12/2 heater cable and another cable about 40 feet of #12/2 will feed the other baseboard.

I am not sure if the #12/2 heater cable is sufficient or I should go with #10/2. Thanks.
 
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Old 08-01-04, 01:39 PM
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I'm not quite sure how replacing 4000 watts of heat with 3000 watts of heat will solve your problem with never kept the garage warm. 12/2 will be enough, but you'll need to downsize the 30-amp breaker to a 20-amp breaker.
 
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Old 08-01-04, 06:06 PM
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Heating wiring size

As I explained before, the 4k fan heater was to far away from the doors and thus not sufficient to heat the garage properly. The two 1.5k baseboards will be close to the doors and able to provide heat where it is actually needed.
What is the relationship between wire size and breaker size? What will happen if I leave the 30A breaker with the #12/2 cables? I don't intend to do so but I would like your answer as an education. Thanks for your time
 
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Old 08-01-04, 06:57 PM
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Heating wiring size

Perhaps I made a mistake when I said that the existing #10/2 heater cable was connected to a 30A breaker. In the panel, there are two breakers connected together with a bar for this garage heating circuit and each breaker shows 30 on its handle. A small tag on the breaker shows among others “2 pole 120/240. Is this breaker considered a 30A or 60A?
 
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Old 08-01-04, 07:51 PM
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The relationship between wire size and breaker size is probably the most fundamental of home wiring concepts. If the wire is too small for the breaker, the breaker will trip after the fire starts rather than before. Most people think that this is bad.

A double-pole breaker with 30 on each handle is a 30-amp breaker, not a 60-amp breaker.

I certainly don't mind you asking these questions, but the nature of the questions suggests that you should read two or three books on home wiring before beginning this project.
 
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Old 08-02-04, 08:07 PM
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As I mentioned above, the power to my first junction box (JB-A) comes from the 30A breaker with about 15 feet of #10/2 heater cable and from there all the remaining heater cables are #12/2. When I replace the existing 30A breaker with a 20A breaker, does it matter that I have about 15 feet of #10/2 cable on this circuit? John I know that it can be frustrating to read stupid questions like mine but I am not an electrician and therefore I try to be as careful as I can.
 
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Old 08-02-04, 08:30 PM
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It's okay to have #10 wire on a circuit protected by a 20-amp breaker.
 
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