beginner wiring ?

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  #1  
Old 01-31-07, 09:53 AM
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beginner wiring ?

The other day, I was replacing a 15A switch w/ a like 15A combo. switch.
Knowing I had to pigtail the neutrals from the box, I referred to my HOME DEPOT book to see what gauge wire to use. It listed 14 gauge wire for 15A circuit and 12 gauge wire for 20A circuit. I checked my circuits at the breaker box and they're all 20A.

My beginner question is this:

a. Is it common to have 15A switches & receptacles on 20A circuits?
(Seemed ok to me)
b. How can I tell if my existing wiring is 14 or 12 gauge (so I can use the same for my pigtail connection)? Currently have 3 wires (black, white & ground) Would I be correct in saying that I have 12/3 wiring???

thanks
 
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Old 01-31-07, 10:04 AM
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If it is on a 20A breaker, you need to use 12 gauge wire.

Some people like to use 15A for lighting circuits and 20A for receptacles. Some people like to use 15A for all residental, as you most likely will never pull that much load in a home. Some other people just run all 20A because 12 gauge is sooo easy to work.

If you just have black, white, and ground, you have 12/2 w/ ground. You don't count ground as a conductor.
 
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Old 01-31-07, 10:17 AM
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If you have all 20-amp breakers, and if it's wired to code, then the existing wire is 12 gauge. If you want to double-check, go to your home center and spend a few pennies to buy one foot of 14-gauge wire, and one foot of 12-gauge wire. Take the samples home to compare.

As is (very, very) often discussed here, 15-amp receptacles and switches on 20-amp circuits are common, safe, and to code. However, 14-gauge wire is not allowed on 15-amp circuits, so be sure to use all 12-gauge.
 
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Old 01-31-07, 10:19 AM
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John I think you mean '14-gauge wire is not allowed on 20-amp circuits, so be sure to use all 12-gauge'.
 
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Old 01-31-07, 10:23 AM
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If you are trying to convert a switch to a switch/receptacle combo you CAN NOT do it. With only the 12/2 wire in the switch box you do not have a neutral. It can not be done without some additional cable being pulled into that box.
 
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Old 01-31-07, 11:12 AM
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thank you, everyone!!
 
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Old 01-31-07, 11:19 AM
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Thanks fuente for catching my error.

And good work joed for discovering that all the questions are moot because the task is inherently impossible.
 
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Old 01-31-07, 03:41 PM
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Yeah, I noticed that too.....the "neutral" you're referring to, if hooked to a switch, is actually a switch leg. The only way it may be possible is if there is more than one 3-wire cable in the box.
 
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