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I currently have a 20A breaker with 12/3 wire leading to a double gang box which contains two 15A receptacles, that leads into another double gang box with two more 15A receptacles.

I'd like to replace the very last receptacle on the circuit with a switch which will be wired to a lamp socket. The lamp socket will have a 60W equivalent LED bulb.

I only have 14/3 wire on hand, which I know is not rated for use with a 20A breaker. Is my assumption that I should not pigtail the 14/3 into the existing 12/3 wiring correct? Or is it okay because it is the last leg of the circuit or because the light will draw like half an amp?

If it is not safe to use the 14/3 wiring, how would it be different if I wired a plug on on the end of the 14/3 wiring and just plugged it into the existing receptacle? This last part is really what I am hung up on.

isherwood
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dholm
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    25ft of 12/3 Romex is cheaper than an electrical fire in your wall, in my humble opinion. – TylerH May 25 '21 at 14:20
  • I'm curious why this question was downvoted. Hopefully not because it asks how to do something inadvisable? Allowing questions only from knowledgeable people would quite defeat the purpose of a Q&A forum. – jay613 May 25 '21 at 15:27
  • I had thought about voting to close but the end section about the cordage was a little different, since another senior member thought the same I agree there are many answers to be found why 14awg can not be used on a 20 amp circuit. If the question was reworded it could be opened but that answer was also given and rejected by the OP – Ed Beal May 25 '21 at 16:10
  • And that's ... why I don't own any #14 wire. The idea is, #14 is supposed to be cheaper, but that only works if you go through wire in builder quantities. For smaller volume, the capital cost of owning spools of both sizes exceeds the cost savings. – Harper - Reinstate Monica May 26 '21 at 18:43
  • To answer your last paragraph, "Building wire" is not "Cordage". Cordage is the made-to-flex cords found on plug-in appliances. Plug-in appliances are UL's bailiwick, so they define the amp rating of cordage. It's higher because cordage is out in the open, not in walls packed with insulation. Putting a plug on building wire violates several codes: 110.3b, 400.8, the inlet rules I can't find, etc. – Harper - Reinstate Monica May 26 '21 at 18:47

3 Answers3

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You can not use 14 awg wire on a 20 amp protected circuit it would violate code and create a fire hazard.

One example is 14 awg wire can fit into back stabs and even on 15 amp circuits these regularly fail on a 20 amp circuit they would be a fire hazard.

You can use an extension cord and there are several reasons this can be safe. Extension cords are temporary and not made for multiple loads like the premises wiring is.

I bet you did not know that 14 awg extension cords usually have a higher ampacity than the wire in your walls. NEC table 400.5.A.1 Example 14 awg has an 18 amp current rating for most types and some are even 20 amps. Why the conductors are not enclosed by the structure and don’t have insulation around them.

So although it may sound ok it is a huge code violation and liability if there was a fire and someone got hurt you would be the one responsible.

Ed Beal
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  • Your answer is not very helpful. Your first paragraph was address in the question, that was understood. You do not address how using 14/3 just for the last leg is different than plugging it in to a receptacle. I am looking to understand what about going through an outlet makes it different, rather than just memorize what code allows. – dholm May 25 '21 at 14:35
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    @dholm paragraphs 3 and 4 directly address using 14-gauge hardwired vs 14ga extension cord. – Fredric Shope May 25 '21 at 15:03
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    The question contains an easy concrete question (can I do X) and a broader theoretical one (why not X if Y is allowed) and this answer does in fact answer both of them concisely. The professionals tend to answer questions in terms of code because they respect it and they know it's mostly written to prevent horrific things from happening AGAIN. You'll learn to like it. Paraphrasing: Extension cords benefit from air circulation and when they start melting you can smell them and eventually they trigger smoke detectors. Cables in walls ignite sooner and fires in walls are worse. – jay613 May 25 '21 at 15:40
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You can't use 14 AWG permanent wiring on a 20A circuit because the code says so.

There is an exception specifically for switches to allow a 15A switch on hardwired lighting (obviously with a max. load of 15A) on a 20A circuit. But that is quite different from the wire itself.

Among other things, we have many questions here that are essentially: I have a light fixture on a circuit and I want to extend from there to a receptacle so I can plug in stuff. Using this example, you want to add a light - the next owner may want to add a receptacle. They'll not realize you have 14 AWG wire but will see the 20A breaker (when they turn off the circuit to work on it) and assume that they can install a 20A receptacle.

Alternatively, since most people never install 20A receptacles, they'll install a standard 15A duplex receptacle (which is legitimate for a 20A circuit) and plug in a typical space heater = 12A continuous on one receptacle and something else drawing several amps on the other receptacle and burn up your 14 AWG wiring without tripping the 20A breaker.

manassehkatz-Moving 2 Codidact
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    The exception that allows a 15 amp switch to be use requires the switch to carry the load (the load has to be less than 15 amps). 15 amp receptacles are allowed on a 20 amp circuit but there must be 2 or more the actual receptacle is wired for 20 amp feed thru. – Ed Beal May 25 '21 at 15:35
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    Ed Beal is right, (ONCE AGAIN!) 15 & 20 amp receptacles are practically interchangeable given the minor restrictions he mentioned. ....I do have a question for Ed: when I built my house, I did all outlet circuits in 12/2 20 amp and used 20 amp outlets (the ones where one of the blades has a horizontal part connected to the vertical part). Are those legal to put on a 15 amp (14ga) circuit....just curious. – George Anderson May 25 '21 at 15:40
  • @GeorgeAnderson It only goes one direction: You can install 15A (as long as at least 2, which can be a single standard duplex receptacle) on a 20A circuit - the 15A receptacles being rated for 20A passthrough and the idea that having 2 allows full utilization of the circuit capacity. But not 20A receptacles on 15A circuit, because that would invite using a 16A continuous device (20A rated, derated for continuous) or 20A non-continuous device on a 15A circuit - both of which could lead to overheating of 14 AWG wire without necessarily tripping the 15A breaker first. In fact a 15A continuous – manassehkatz-Moving 2 Codidact May 25 '21 at 15:44
  • load might never trip a 15A breaker (and 16A could take a long time) but would not be good for the 14 AWG wire (which is why 15A is supposed to only have 12A continuous). etc. – manassehkatz-Moving 2 Codidact May 25 '21 at 15:44
  • @manassehkatz-Moving2Codidact I think you misunderstood my question, which was: Is a 20 amp receptacle OK, to put on a 14/2 cable protected by a 15 amp breaker? Code is vague on this. Odd part of the code that allows interchangeability of outlets rated at 15 or 20 amps. I wouldn't put a 20 amp outlet on a 15 amp circuit, even if properly protected, I was just curious if it was even allowed....probably shouldn't be. – George Anderson May 25 '21 at 16:50
  • @George I understood the question. The answer is "No" and I was trying to explain why. – manassehkatz-Moving 2 Codidact May 25 '21 at 17:25
  • @manassehkatz-Moving2Codidact Not meaning to belabor this, but how is a 16A continuous device plugged in to a 15 amp outlet any different than it being plugged into a 20 amp outlet if both were on 14ga wire protected by a 15 amp breaker? Again, I wouldn't do it, but I don't understand your explanation. The breaker sizing is to protect the installed wiring, not devices. So if 15 amp breaker on 14 ga wire, what's the issue? – George Anderson May 26 '21 at 00:31
  • The difference is that you won't find a properly designed device drawing more than 12A continuous that is capable of being plugged into a 15A receptacle. Such a device can only be plugged into a 20A receptacle because of the required plug design. – manassehkatz-Moving 2 Codidact May 26 '21 at 00:46
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I sounds to me like you have a MWBC (multi wire branch circuit) that's probably feeding outlets in a kitchen. Have I divined this correctly? If so, those are required to be DEDICATED outlets and can't be shared with other outlets or lighting.

Next point: You can't use 14/3 on a 20 amp circuit unless you swap out the breaker for a 15 amp breaker and mark the wires in the panel stating part of the circuit is 14 ga. ...OH BUT WAIT, if kitchen outlets, they are required to be 20 amps, at least 2 circuits.

Lastly, likely yes, if fitted with a plug and plugged into a receptacle. (you are in the USA, right?) you could do that, but why 14/3? why not just a SJ lamp cord? Much easier to work with. My last worry is that an inspector might view 14/3 NM cable stapled down as a permanent installation and require physical protection according to NEC code.

George Anderson
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  • No, this circuit is an extra basement room. I do not have SJ lamp cord on hand but I do have extra 14/3. The real part I don't understand is what makes it safer to have either lamp cord or 14/3 plugged into a receptacle versus pig tailed in? – dholm May 25 '21 at 14:30
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    @dholm It's a code thing. Overcurrent protection is to protect permanently installed wiring, not devices connected to it. For example, if you had a bathroom heater that shorted out(true short) the breaker would trip to protect the installed wiring. The device (heater) is probably toast at that point anyway. Once you use a receptacle and plug, it becomes a "device" that's not covered by the NEC and not considered permanently installed wiring. Good devices might have a UL rating, but not always. ...comment continued next, bc I'm running out of space on this one! – George Anderson May 25 '21 at 14:51
  • I tend to think of wiring methods in 3 ways: 1) not to code and unsafe, 2) not to code, but probably fairly safe, and 3) Up to code and safe. Of course I always personally do #3. It's safe to use the 14/3 on a plug /socket. It just can't be permanently installed (pigtailed, wired in the wall, or conduit without derating the breaker according to code. Most table/portable lamps are fed with 18 ga lamp cord, plugged into a 15 or 20 amp circuit. So if you use the 14, you'll be safe, but if hard wired, you won't be code legal. – George Anderson May 25 '21 at 15:00