Tap off a 20A outlet to feed 15A switch/light

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  #1  
Old 10-26-06, 07:39 AM
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Tap off a 20A outlet to feed 15A switch/light

Hello all!

At the far end of the barn, outside on the peak, I'd like to install a typical 15Amp motion flood light. There's a 20amp outlet (last of three on its circuit) nearby.

Question: I'd like to tap off the 12/2 20A outlet using 14/2 15A wire, into a 15A switch, then the light. The barn walls are all open, no sheetrock.

Can I do this?

On paper it looks OK, but will the inspector claim that the 20A circuit must have all 20A wire/fixtues? I do not see a heat issue at the end of the line, but there may be a general CODE issue?

The alternative is to run a seperate 14/2 wire, just for the one light, from the sub panel that is at the other end of the barn, about 65' away. Seems like a waste.

Or to run 12/2 wire from the outlet to the light. But I can't find a switch rated for 20A at the home supply store. Can I place a 15A switch in a 20A circuit? Then why not 15A 14/2 wire?

Help me understand. Thanks.
 
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Old 10-26-06, 07:57 AM
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You must use 12/2 wire with a 20 amp circuit.

However, before tapping into the circuit, you must make sure the circuit can handle the additional load. You should only load a 20 amp circuit to about 1920 watts.
 
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Old 10-26-06, 08:00 AM
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No, you cannot do this. And you must have funny paper if you think it looks good on paper, because it most surely does not.

Assuming you are in the US, code (the NEC) reequires that all wire used on a 20 amp branch circuit must be at least 12 gage wire. Period. You are allowed to use 15 amp receptacles (note the 's' at the end of receptacles) on a 20 amp circuit. Code requires that a switch must be sized for the load. This means that a 15 amp switch is fine for this setup.
 
  #4  
Old 10-26-06, 08:55 AM
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Not a problem...

The above posts are correct about the wire size... so, run 12 gauge to the fixture - then install your fixture and enjoy!
 
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Old 10-26-06, 11:36 AM
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Tap off a 20A outlet to feed 15A switch/light

OK OK,

I will use 12/2 wire (and a 15A switch?) and play it safe. Thanks all.

But, unfortunately, I don't actually understand why. Especially, why I'm able to place a 15A weak link switch in the middle of this 20A circuit?

If the circuit is overloaded, then the 15A rated switch will fry (weak link). If the switch won't fry because it is upstream of the 15A load (light), then neither will the 15A wire fry.

In this case, the tap is off the last outlet (#3) in the circuit. The heat should build up between the outlets' load and the breaker. I don't see how heat would build up between the switch along the 15A wire to the little light? Funny paper?
 
  #6  
Old 10-26-06, 11:58 AM
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Nah... funny code!

But, think of it this way.... somewhere down the road, someone else say's "Hey, I've got a 20 amp circuit that I can use in this garage"... They run 12/2 to their fixture, which needs lots of power - unfortunately, you, in earlier years, ran 14/2 along the same circuit - Now, you've got an Ooooops.....
 
  #7  
Old 10-26-06, 03:10 PM
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To clarify: Yes, you may install the 15A switch on the 20A circuit as you describe, provided you use #12 cable. There is no issue with using a 15A switch, or with mixing lights and receptacles.

I still have no idea why the code allows so much use of 15A appliances and devices on 20A circuits, it seems completely contrary to everything else in the NEC. I'm sure there's a perfectly logical reason, but I haven't heard it yet. Either way, this is legal and absolutely ubiquitous, so go on and tap that duplex receptacle with confidence!
 
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Old 10-26-06, 03:53 PM
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> But, unfortunately, I don't actually understand why.

Ultimately the code is a balance of safety and cost. I think this is one of those situations where they look at a 15A switch which is $0.49 and a 20A switch which is $2.50 and recognize that overloading a switch is so unlikely in a residential situation that they will allow the 15A switch to knock a hundred bucks off the price of every newbuilt home in the USA.

They make these concessions with the hope that trained professionals will recognize when a wimpy 15A lightswitch is inadequate and install a spec-grade 20A switch where appropriate.

Moreover, the 15A switch can easily be replaced if it burns up or changed to a 20A switch if future needs mandate it. The cable in the wall cannot be replaced without much more hassle.

As a side note, most of these sorts of exceptions only apply to single-family residential homes where the extra cost burden isn't justified by the risk of failure. Commercial and multi-family residential usually are not granted so many exceptions.
 
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Old 10-26-06, 04:05 PM
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You may use the fixture because the wireing that comes from the factory is not covered under the national code. the fixture is ul listed for this purpose, meaning that it has been tested this way, and is safe.

You may use a 15 amp switch on a 20 amp circuit when the load is less than 15 amps for mostly the same reason. The difference between the switches is what the contacts inside the switch are made of, not the metal conductors inside the switch. Basicly the actual parts that touch eachother and open are better quality on the 20 amp switch so they can obsorbe the arc of opening and closing better.

if you loaded a 15 amp sw with under 20 amps but over 15 you would just burn out the contacts sooner, but you are not likely to cause a fire.
 
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