Basement Finishing/Wiring

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  #1  
Old 02-23-05, 07:43 AM
Jwichman
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Basement Finishing/Wiring

Converting my unfinished basement to a finished room. Have the first of probably many questions on the electrical portion.

First, I have two existing circuits coming into the basement, one for lighting and one for outlets (not counting furnace and washer dryer circuits). When examining these two circuits I found that each have a 20 amp breaker at the panel, are wired with 12/2 w ground romex, and then contain 15 amp fixtures (outlets and switches). I checked a couple circuits in the finished portion of my house and found the same 20 amp breaker with 15 amp outlets. Is this ok?? Are these considered 15 or 20 amp circuits? What happens if 16-20 amps are pulled through a 15 amp outlet?

Second, how many wires can be installed in a 22.5 cu in plastic wall box with a single pole light switch? Is there a rule of thumb that says you can wire x number of wires per cu in of box that can be used for all sizes of plastic wall boxes? When counting wires a 12/2 w ground and a 12/3 w ground count as 6 wires (count 1 ground and all hots and neutrals)?

Thanks for the help
 
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Old 02-23-05, 08:23 AM
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15-amp devices are specifically allowed by code on a 20-amp circuit. Don't worry. They can handle it.

Most wiring books describe how to compute box fill. If you don't already have some wiring books, get several. Start with Wiring Simplified, a $6 green paperback available in the electrical aisle of most Home Depot stores, or at Amazon if not.

When using #12 wire, each "unit" is counted as 2.25. So a 22.5 cubic inch box can hold 10 units. The switch counts as two, leaving 8 for wires. All the grounds taken together count as one, leaving 7 for other wires. So you can have up to seven wires that are black, red or white. That would mean, for example, two 12/2 and one 12/3.
 
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Old 02-23-05, 12:03 PM
Jwichman
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Additonal Question and a Clarification

Thanks for the quick response to my questions. I have a couple of additional questions:

I have a 6 inch stud wall (2X6 studs). I would like to mount light switches in the same stud cavity on both sides of the wall. One side will have a 4 gange switch box and the other side a 2 gang switch box. Both boxes are the plastic type. The boxes will physically fit in the area of a 2x6 stud provided that the back of the boxes are in direct contact with each other. Any problems with this?

Also, in the response to my initial post regarding the number of wires allowed in a wall box, it was stated that a switch counted as 2 units. Is a 3-way switch counted as 3 units and a 4-way switch counted as 4 units.

Thanks,
 
  #4  
Old 02-23-05, 12:10 PM
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No problem with back to back boxes.

All switches count as two.
 
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