Circuit Load

Old 01-30-03, 11:39 AM
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Circuit Load

I was an electrician's helper for a while but never calculated load requirements...I'm currently finishing two rooms in the room will be an office and the other a bedroom.

Currently there is 12/2 run in each of the rooms, each on a separate circuit, I want to put a computer, 4 tube florecent light, and a plug in electrical heater in each room.

Questions: Should I be using a 15 or 20 amp breaker and what is the maximum wattage heaters I can use in the rooms?


Last edited by ltbsolomon; 01-30-03 at 12:51 PM.
Old 01-30-03, 01:23 PM
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On 12/2 wires the maximum size of breaker that can be used is a 20 amp. Which on a 120v circuit it is 120 multiplied by 20 to get the maximum wattage. At this point you can only load to 80% of the max so the formula is votlage x Amps x 80% = 1920watts.

Therefore wattage divided by voltage multiplied by 1.25 will tell you the amps needed. Recepticles and lighting are not to be put on a breaker larger then 20 amp and the minimum of 15 amp. If you exceed the 1920watts then you'd have to install another cirucit.
Old 01-30-03, 05:41 PM
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Even two 20-amp circuits is going to be marginal. A 20-amp circuit can supply a maximum of 2400 watts. A typical portable space heater that you buy at the home center is 1500 watts. That leaves only 900 watts for everything else in the room. The four-tube fluorescent light is 120 watts. The computer, depending on the size of the monitor and how much you have connected to it, could take another 200 to 500. You might not have enough left to run a television.

Putting two circuits in each room instead of one will give you more flexibility for the future.

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