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Old 12-29-2010, 12:03 PM   #1
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baseboard heaters in parallel


right now i have one heater installed with a thermostat on the wall in one room. i want to put another one in a separate room with its own thermostat using the same wire from the basement. the heaters are 240 volt, 1500 watts. i used 12/2 wire up. its on two 15 amp breakers. is there a way to use this same wire?

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Old 12-29-2010, 12:59 PM   #2
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baseboard heaters in parallel


i am thinking if i put a box in the attic i can tie into the wire coming up, and switch the breakers to 20 amp and it should be ok.

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Old 12-29-2010, 01:08 PM   #3
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baseboard heaters in parallel


3000 watts / 240 volts = 12.5 amps.
Electric heaters are treated as continuous load. 15 amp circuit * .8 = 12 amp maximum. As long as you've used 12 gauge all the way, you can junction the wire from the breaker before the first tstat and run a new line to your proposed new tstat. Change the 2) 15 amp breakers to a double pole 20. Don't forget to remark your whites.
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Old 12-29-2010, 01:14 PM   #4
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baseboard heaters in parallel


i ran 12 all the way to first tstat then from there to the heater is 14. but i want to tie in before the first tstat for the other heater. also where did .8 come from in the calculation?
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Old 12-29-2010, 01:25 PM   #5
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Heat is considered a continuous load, so the circuit is limited to 80% capicity.
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Old 12-29-2010, 01:26 PM   #6
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baseboard heaters in parallel


With 14 gauge wire continuing on to one heater, you may not up the breaker to 20 amps.

The 0.8 is an arbitrary number specified in the National Electric Code to multiply the amperage rating by when there are hard wired (not plugged in) appliances of certain kinds (designated as continuous loads) on the circuit.

Is it easy to string a new cable (12 gauge) to the first heater?

By the way, the total circuit load of 12.5 amps is less than the existing breaker rating of 15. The total load of 12.t amps through the first 12 gauge leg is less than 80% of 20 amps (16 amps) for 12 gauge. The load to each heater via its 14 gauge wire is 6.25 amps well within the 80% of 15 amps for 14 gauge.
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Old 12-29-2010, 01:28 PM   #7
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For a continuous load, like a heater, you can only use 80% (.8) of the maximum capacity. I do not think that even with a 14 gauge dedicated line going from your existing stat to heater and the load is only 6.25 amps, you can increase the breaker to 20. I'm sure a pro will chime in.
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Old 12-29-2010, 01:59 PM   #8
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baseboard heaters in parallel


No. The experience of another user on here shows why.

Imagine the heating element breaking inside the tube and shorting to the case. The element is now still in the circuit, but is shorter. A shorter element has less resistance, and pulls more current.

It may seem that you only have a 6.25A load, and that 14awg wire would be safe (still not legal either way), but there are certainly ways in which the heater can wind up pulling more like 18A, which, of course, will not trip a 20A breaker, but will exceed the 15A limit of the wiring.

That's the science answer. The code answer is simply "thou shalt not put 14awg wire on a 20A circuit."
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Old 12-29-2010, 02:08 PM   #9
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Thank you for the science answer.
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Old 12-29-2010, 02:33 PM   #10
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i could replace the 14 piece with 12. its easy to get to. or should i just hook up the second with 14 also and leave the 15 amp breakers in?
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Old 12-29-2010, 02:37 PM   #11
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oh wait 80% of 15 amp is only 12. the two heaters are 12.5. so i guess i should replace with 12 gauge and go 20 amp.
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Old 12-29-2010, 02:41 PM   #12
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If you have the chance, replace it and the breaker.
This way, if you decide you need a bigger heater, you could add another without much work.
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Old 12-29-2010, 03:00 PM   #13
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yeah but if i did add another that would 18.75 amps which exceeds the 80% limit of 12 gauge wire anyway. so its really of no use.
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Old 12-29-2010, 03:01 PM   #14
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i guess there would be some room for a bigger heater though. another 3.5 amp would still be available before the 80% is exceeded.
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Old 12-29-2010, 05:42 PM   #15
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I would hook up the second heater from the existing thermostat box and keep the circuit at 15 amps until I could replace the 14 gauge section with 12 gauge at my leisure. The shared 12 gauge wire section is not being oveloaded.

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