A friend had a question for me, which means now I have a question for you guys

They moved a light switch from one side of the doorway to another. The wire to the switch that also feeds another light switch and two wall outlets was about 1 1/2 feet too short so he extended it. The wiring is 14 gauge, and the 1 1/2 foot extension is 12 gauge.

The only answer I had to his questions (one also being about the joining of the two) was to be sure to enclose it in a metal box after capping it with wire nuts.

I don't understand electricity flow enough to understand what will happen with the change in the wire size. It seems it will speed up when it gets to the 12g, but then what happens when it gets to the switch itself and then moves back to the slower 14g and then on to the other light switch and outlets?

Thanks for any help for me on this one.

Kay

 

Electricity moves the same speed no matter what. In branch circuits, 12 gauge is rated to safely carry 20 amps, while 14 gauge is rated 15 amps.
Since he added a LARGER size wire, I see no problem with his installation.

 

You can safely use 12 gauge wire on a 15 amp circuit.

Many people, however, don't recommend mixing wire sizes on a circuit without a clear amd legitimate reason for doing so.

The danger is that someone later on will attampt to extend this circuit by adding a receptacle outlet. They just might see 12 gauge wire and think that they can safely add a 20 amp receptacle outlet. This would of course, not be legal, and would be a fire hazard.

Now it is unlikely that someone would make this mistake when wiring from a switch, especially if the circuit is a switch loop, but it could happen.

Your friend could have very easily bought a few feet of 14-2 wire, probably at the same store where they bought the new switch box. The home improvement stores sell the various wire sizes by the foot, in addition to selling the larger rolls.

 

Also, the box in which the splice was made must remain accessible.

 

racraft...your incorrect with your statement. (the danger is that someone later on will attampt to extend this circuit by adding a receptacle outlet. They just might see 12 gauge wire and think that they can safely add a 20 amp receptacle outlet. This would of course, not be legal, and would be a fire hazard. )

there is no danger if you add a 20 amp receptacle to a 15 amp circuit. The danger is if you change the breaker out from a 15 amp to a 20 amp breaker because of noticing the 12 gauge wire...

 

Adding a 20 amp receptacle to a 15 amp circuit would allow the use of electrical appliances that draw in excess of 15 amps of current. Theoretically the breaker should trip before it poses a problem, however, the wires are going to be overloaded until the breaker does trip. Eventually, after this cycle repeats itself several times, the wires will probably be damaged to some extent.

While I agree that swapping out the breaker poses a greater threat, installing a 20 amp receptacle on a 15 amp circuit is also asking for trouble.

The bottom line is, it is usually bad practice to mix wire sizes on the same circuit and should be avoided.

 

Not really, How many devices in your home have a true 20 amp male end???

 

None, but if I did have any they would definitely not be on 15 amp circuits. Although that's not really the point. Just because most people don't have a true 20 amp appliance , that doesn't make it okay to put a 20 amp receptacle on a 15 amp circuit. Not if you are looking for a code-compliant installation anyway.

 

Okay, you guys have gone way over my head now. My concern was not future additions, etc, but concern about the possible damage to the wiring and I guess code because on the consumer end (them) it can mean whether or not insurance would cover any damages due to fire.

I will recommend that while they are enclosing the joined wires in an accessible metal box, to go ahead and replace the short piece of non-matching gauge wire while they're in there. I believe I have some 14g in my shop.

Thanks!

Kay

 

hotarc, I appologize. I know i was nit-pickin about how many 20 amp male ends that are in the average home. Bad day.