Breaker and wiring for baseboard heaters

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  #1  
Old 02-14-05, 03:10 AM
boardsonfeet
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Exclamation Breaker and wiring for baseboard heaters

I am installing two electric baseboard heaters in my soon to be finished basement and need advise on what size breaker and wiring I need to use. The first unit is 220 V/ 2000 watts and the other is 220 V/ 1500 watts.

I will use a line voltage thermostat (Honeywell CT1950A or CT62B), so will I have to run one 30 amp double throw breaker with #10 wire for the whole circuit, or just to the thermostat and then #12 to each heater?

Or, is there a completely different/ correct way? I will have to run the wiring in the next few days, so any help or suggestions will be greatly appreciated. The units are Fahrenheat/ Marley models F2548 & F2546.

Thanks
 
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  #2  
Old 02-14-05, 04:16 AM
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You must use 10 gauge wire for the entire circuit. You cannot use a smaller size wire on a portion of a circuit just because the anticipated load on that portion of the circuit is less than the load of the entire circuit.
 
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Old 02-14-05, 01:47 PM
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Why use 10 gauge wire?

2000 watts + 1500 watts = 3500 watts.

3500 watts divided by 240 volts = 15 amps (rounded off to the next higher number).

15 amps X 1.25% = 19 amps.

Use #12 wire and a 20 amp two-pole circuit breaker.
 
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Old 02-14-05, 02:30 PM
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In thinking about my original answer, I may have hurt more than helped.

Thinman's post correctly computes the current draw, at just less than 15 amps. This is not a continuous draw, so you don't have to figure the breaker at 125% as he did. However, it's not a bad suggestion.

If this were my house, I would use 12 gauge wire and a 20 amp breaker. However, if you think you may want to someday put another baseboard heater on this same circuit, then you might want to run 10 gauge wire. I would still use a 20 amp breaker until I added that new load.
 
  #5  
Old 02-14-05, 02:36 PM
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Yes you do have to use the 125%. It's not the continuous load rule, but this falls under a different 125% rule.

(Bob, you really should buy yourself a copy of the NEC, just for your own amusement.)
 
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Old 02-14-05, 02:55 PM
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My apologies, I stand corrected.

John, when did this change? The baseboards heaters in my basement do not folow the 125 percent rule for the breaker (it is close).
 
  #7  
Old 02-14-05, 05:09 PM
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Sorry Bob, I don't know how old the rule is. How old is your baseboard heat?
 
  #8  
Old 02-14-05, 07:22 PM
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My heat is not that old. 3 years. It's in the now finished basement, and we have only used it three times, as we only need it when it is extremely cold, and it supplements the furnace.

I'd have to double check the units, but I think we have 4000 watts on a 20 amp circuit. That of course would translate to 16.67 amps, which would jump to 20.83 amps at 125 percent.
 
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Old 02-15-05, 05:55 AM
boardsonfeet
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Thanks for your help

I had looked up some of these calculations myself after posting and figured on the 20 amp breaker with #12, but I feel better that you've now confirmed it.
 
  #10  
Old 02-15-05, 06:31 AM
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Bob, look carefully at the specs. Many appliances are rated at 125 volts. For example, we get questions here about why an 1875-watt hairdryer can have a 15-amp plug. The answer is in the fine print. The hairdryer says "1875 watts at 125 volts". Maybe your heater is rated at "4000 watts at 250 volts".
 
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