Paralleling 14 guage wire on 20 amp circuit

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jselesk2

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Hello,

The information I've found seems to be conflicting regarding this topic. Let me give a simple example - a circuit supplied by a 20 amp breaker is wired with 12 guage wire. It supplies several outlets and lighting fixtures. Suppose that somewhere along the circuit, 14 gauge wire is paralleled off the 12 gauge wire to supply a single 60 watt light bulb. Is this allowed? If not, why? Seems perfectly fine to me because the 14 gauge wire in this case will only draw as much current as the light bulb, which is far less than 15 amps.
 
Thanks guys. After reviewing the articles mentioned, it appears that this is not allowed, unless what I'm doing falls under the "tap conductor" criteria. So, in my example, this would not be allowed unless the 14 gauge wire extended a maximum of 18 inches beyond the light bulb. Is that right?
 
jselesk2 said:
Thanks guys. After reviewing the articles mentioned, it appears that this is not allowed, unless what I'm doing falls under the "tap conductor" criteria. So, in my example, this would not be allowed unless the 14 gauge wire extended a maximum of 18 inches beyond the light bulb. Is that right?
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Paralleling that small of a conductor isn't allowed at all for general power and lighting circuits. Tap conductors are allowed in certain situations, said tap conductor can possibly be only 18 AWG in some situations as well, but there are condition that apply. Common practice I run into a lot that was never acceptable to NEC is to run 12 AWG to all the receptacles in a room and then tap off with 14 AWG to go to the light, or to just use 14 AWG for the "switch loop" of the light.

One of the most common taps like mentioned here that is compliant is to place a junction box above a "troffer" and install "tap conductors" of 16 or 18 AWG in flexible metal conduit between the two.
 
It seems Section 402 on Fixture Wires seems more relevant than call the #14 wire a Tap. I realize that 'Fixture Wires' are meant to be within the fixture, but it seems this situation, where a single small load is supplied by the #14 wire. And yes 402.11 says fixture wires shall not be used as branch circuit conductors. From a physics point of view. If one can use a #18 gauge wire for a fixture wire, why couldn't one use a #14 to supply that #18 gauge fixture wire.
 
tsogrady said:
From a physics point of view. If one can use a #18 gauge wire for a fixture wire, why couldn't one use a #14 to supply that #18 gauge fixture wire.
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From a physics point of view a number of things in the NEC are over kill but, the code is the code.

Roger
 
tsogrady said:
If one can use a #18 gauge wire for a fixture wire, why couldn't one use a #14 to supply that #18 gauge fixture wire.
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Possibly because a switch leg could have a lot of load added, such as a receptacle or more lights, while a fixture wire very little, i.e., the load is known and limited.

For example, you would never want to use small-gauge fixture whips to jump from fixture to fixture.
 
Roger said it best, it is what it is even if it doesn't make sense. I can use a 15 amp switch on a 20 amp circuit as long as the load doesn't exceed 15 amps. I can even use a 600 watt dimmer on that same circuit. Is what it is. :)

roger said:
From a physics point of view a number of things in the NEC are over kill but, the code is the code.
Click to expand...
 
LarryFine said:
Possibly because a switch leg could have a lot of load added, such as a receptacle or more lights, while a fixture wire very little, i.e., the load is known and limited.

For example, you would never want to use small-gauge fixture whips to jump from fixture to fixture.
Click to expand...

Larry,
Thanks for the practical answer. Yes someone could screw in a light socket receptacle adapter into the light in question, and then plug in an electric heater, overloading the #14 or even #18 gauge wire. Dumb, but it could happen.

The answer about Code being Code, I find demeaning to thinking electricians. I believe it is important to know the why. I find this leads to better installations.
thx
 
tsogrady said:
Larry,
Thanks for the practical answer. Yes someone could screw in a light socket receptacle adapter into the light in question, and then plug in an electric heater, overloading the #14 or even #18 gauge wire. Dumb, but it could happen.

The answer about Code being Code, I find demeaning to thinking electricians. I believe it is important to know the why. I find this leads to better installations.
thx
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Well, code is code and I'm sorry that hurts your feelings but, if you want to find out why something is in the NEC go to the NFPA website and start researching past ROPs and ROC's, it can be a long task but there is a good chance you will find a proposal that started the rule.

Roger
 
tsogrady said:
From a physics point of view. If one can use a #18 gauge wire for a fixture wire, why couldn't one use a #14 to supply that #18 gauge fixture wire.
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This will likely not be a completely satisfactory answer. But it is all I can offer.

The difference is that the #14 is part of the branch circuit and the #18 is part of the fixture. Why is that relevant? Because the fixture is tested by its manufacturer in accordance with the rules for the listing. As long as it passes the tests, it can be sold and installed. The #18 wire is attached to the fixture while those tests are being conducted. That is why we can have confidence that it is OK for the #18 wires to be there.

But the #14 is not tested as part of the listing. So it must be treated the same way that other feeder and branch circuit wiring is treated. That requires that it be protected against overcurrent in accordance with its ampacity. Since it is one of the “small conductor” sizes, it must also be protected with a breaker or fuse rated no higher than 15 amps (despite it having a higher ampacity in the tables). So you can’t protect it against overcurrent with a 20 amp breaker.

Finally, the installation described in the first post would not meet the requirements of the tap rules. All of the tap rules require that the overcurrent protection that is not provided at the point of the tap (which is what makes this a tap in the first place) must be provided at the other end of the tap conductors. The OP talked about tapping a #14 onto a #12 and connecting it to a light fixture, without putting an overcurrent device upstream of the light fixture. That would violate the tap rules.

 
charlie b said:
This will likely not be a completely satisfactory answer. But it is all I can offer.

The difference is that the #14 is part of the branch circuit and the #18 is part of the fixture. Why is that relevant? Because the fixture is tested by its manufacturer in accordance with the rules for the listing. As long as it passes the tests, it can be sold and installed. The #18 wire is attached to the fixture while those tests are being conducted. That is why we can have confidence that it is OK for the #18 wires to be there.

But the #14 is not tested as part of the listing. So it must be treated the same way that other feeder and branch circuit wiring is treated. That requires that it be protected against overcurrent in accordance with its ampacity. Since it is one of the “small conductor” sizes, it must also be protected with a breaker or fuse rated no higher than 15 amps (despite it having a higher ampacity in the tables). So you can’t protect it against overcurrent with a 20 amp breaker.

Finally, the installation described in the first post would not meet the requirements of the tap rules. All of the tap rules require that the overcurrent protection that is not provided at the point of the tap (which is what makes this a tap in the first place) must be provided at the other end of the tap conductors. The OP talked about tapping a #14 onto a #12 and connecting it to a light fixture, without putting an overcurrent device upstream of the light fixture. That would violate the tap rules.
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Hold on there, 240.21(B) is for feeder taps and there is overcurrent protection on both sides of the conductor - but the one that actually is sized per conductor ampacity is at the load end.

240.21(A) is for branch circuit feeder taps - and there are some specific cases where the "tap conductor" can have lesser ampacity then the overcurrent protection, and such protection is on supply side.
 
Sure, if that's all the load that was ever on that wire, number 14 would be fine for a 60 watt bulb. To continue this train(wreck) of logic though, for the same 60 watt or half an amp load,, number 16 would also work, so would number 18, so would 20 gauge t-stat wire
.. I believe that even Cat5e with 24 gauge conductors will carry a 0.5a load... you could even use the green pair for the ground. :happysad:

There has to be a cut off somewhere, and with the NEC being as conservative as it is, is just as well that it does not allow 14 gauge wire on a 20 amp circuit, with few exceptions that do not include lights.

That 14 gauge wire is allowed on a 20 amp circuit for switch legs has got to be one of the top 3 handyman wiring myths. Every time I open a switch box and find 12 and 14 intermingled on the same circuit, I know it was wired by a handyman, nothing was inspected, and to expect anything.
 
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