14 and 12 Gauge and other Beginner Questions

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Old 07-25-07, 07:37 AM
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14 and 12 Gauge and other Beginner Questions

Just a couple questions for my basement project...
I came into some brand new 12/2 250ft wire for 10 dollars and want to use it...the thing is I will need just a little bit more than that and want to know if it is ok to use any combination of 12 and 14 gauge? For example could my home runs to the box be 14 guage while the rest between lights and receptacles use 12? I have 20 and 15 A breakers to use if that makes a difference.

I'm also curious as to whether or not I can have a run from the box on one wire that splits in a junction box using wire nuts to three switches controlling 3 different areas of lights in one big room (no more than a total of 10 lights downstream of the one original wire to the box on one breaker.)

One more (sorry)...the previous builder left up a couple of work lights in our basement...if I want to redirect any of these wires or extend the runs, can I simply use a junction box with wire nuts and some new wire to make existing runs longer?

Thanks (and I promise to have my work looked at by an inspector...just in case some reading this are sweating at my naivety), Rory
 
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Old 07-25-07, 07:55 AM
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You are allowed to mix 14 and 12 on the same circuit HOWEVER you must size the breaker to the smaller wire size. In this case you would use a 15 amp breaker. It is not advisable to do this however since it can sometimes cause confusion later when someone thinks they can up the breaker to 20 amps.

I would advise to use the same gauge wire any circuit. If you don't have enough #12 for the entire job then use the #14 for a separate circuit with only #14 wire. That would be a good choice for lighting circuits.

You can bring a wire in a box and split to use for three light switches.
 
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Old 07-25-07, 08:00 AM
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14 gage wire can only be used on 15 amp circuits. If you have 20 amp circuits you must use 12 gage (or higher gage) wire.

I suggest that you do not mix wire sizes on a circuit. I also suggest that all your receptacle circuits be 20 amp circuits. If you want, you can make your lighting circuits 15 amp.

Mixing wire sizes can lead to confusion or mistakes down the road if someone does not know that there are different size wires on the circuit.

It is legal to split a circuit at a junction box to go several different directions, or even to extend a circuit. However, all junction boxes must remain permanently accessible. This means they cannot be covered by drywall. If they do not contain a switch or receptacle, they must have a blank cover installed and that cover must be accessible.

I do not recommend that you install junction boxes just to make it easier to do the wiring or to save wire. Every junction is a potential problem down the road, if the junction should fail. I only suggest that you make junctions at receptacles and switches, even it means more wire is needed.

I would not use the builders temporary circuit unless they were where I needed them or they could easily be moved. Saving a few bucks is not worth it if it costs you down the road. If you douse those circuits, make sure they are properly done. Something a builder throws up for temporary use may not necessarily be completely to code either due to it's temporary nature or because things have changed from when it was originally put up.

You should buy and read two or three books on home wiring. There are many questions you have not asked that will get you if you don't understand the rules. Start with the book "Wiring Simplified" (available at the big box stores and on-line) and then get one or two more. Look for books with pictures and written in language you can understand.
 
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Old 07-25-07, 09:11 AM
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Thanks for fast reply!!!!

I'm following what has been said and understand. About the junctions...you mentioned making junctions at switches and receptacles...it seems like the switch boxes just couldn't fit all of the splits I would like...is it a case of just dressing your wires neatly to make them all fit...I don't want to do any "cramming" so I thought a box would be a little neater...maybe I'll give a try making junctions at switches and receptacles...
How many black can I connect to one switch or receptacle? Thanks again! Rory
 
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Old 07-25-07, 09:22 AM
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Box fill governs how many wires can enter a box. The calculations are not straight forward. Boxes are a certain volume, in cubic inches. Each wire (not each cable, but each wire) entering a box counts as so many cubic inches (depending on wire size). All ground wires count as one wire. The device itself (switch, receptacle) counts as so many cubic inches. Then you have to deal with clamps on the box. The book I mentioned and others will define this for you.

In general, if you have to cram or it;s difficult, then you have probably exceeded box fill.

Design your layout to minimize the junctions necessary. Again, use more cable to avoid junctions and to avoid exceeding box fill requirements.

One wire per screw terminal. If you have more wires than one per screw then you need to use a wire nut and a pigtail. Do not use back stab connection. Back wire receptacles and switches accept two wires per connection.
 
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