Using #14 wire for one light on 20A breaker

[maradcliff]

I am wondering how the code views this. I was just wiring my barn and ran out of 12-2 romex. Rather than buy more, I decided to just use

14-2 since I had 200 feet of it. This 14-2 is only going to one light, one of those porcelin fixtures that are rated at 100W.

As far as safety, I am not worried in the least. It's only going to run one 100W bulb (or less). As far as being inspected, I am also not worried. In barns and sheds they really dont care, unless there are bare wires or some obvious danger source. I'm just curious how the code views that? For example, if I but a common house type ceiling fixture, they generally have 8 inches or up to several feet (on a chandlier) of #14 standed wire as part of the fixture. So, if I am running a 20A circuit I am already using #14 in the circuit.

In my case, I have one center light fed by #12, and one light on the left another on the right. Each of those lights are fed off the center light with about 16 feet of #14.

Thanks

Mark

[Toller]

The problem, as the NEC sees it is two fold. If somehow the light started drawing too much current, the breaker would not protect the wiring. Or, if that seems too farfetched, someone after you might change the light without realizing the wire is inadequate.

[dpb]

If you don't care, why ask? :)

By code, it's not up to snuff, because code is designed to protect the fixed wiring, not the fixtures or other end load. I agree it's not an inherent safety hazard as described as long as the use remains as is.

I would be somewhat suprised if an inspection (assuming you're in a place where zoning applies and it will be inspected) didn't point it out as a deficiency, but that would be dependent on, as you say, what your local inspector's penchant/foibles is/are...

Of course, you can easily alleviate the issue by putting a 15A breaker in the panel for that lighting circuit and be over-sized rather than under-sized in a portion of the circuit.

Me being me, I'd probably have just got another roll of 12 and finished it out simply for the self-aesthetics of the job and knowing that eventually I'd use that roll for other stuff around the place, but again, that's just me having had to grow up under my grandpa and dad... :)

[Steve Barker LT]

OH, but that would have cost $8.

[Bill]

Hummm... I just figured out why there are so many barn fires in which insurance companies refuse to pay for damages!

[Doug Miller]

As a violation.

Fixture wires generally have a much higher temperature rating than supply wires, which enables them to carry higher current on smaller wires.

[Goedjn]

Back when they still used knob and tube, you'd just stick a ceramic fixture with a 15A fuse in it between the heavy wiring and the lighter wiring.

Do they still make things like that, or is it a full-blown sub-panel or nothing?

--Goedjn

[Abe]

Why not avoid any potential problems and just buy a 15 amp breaker for a few bucks?

[emailaddress]

Where can you buy 50 feet of 12-2 for $8. Please tell me. I'll but

100 rolls immediately.

[Don Klipstein]

Code actually requires all wiring in a branch circuit to be of the same size. However, I cannot guarantee that this item is in the NEC as opposed to being merely in a local building code. I am under the impression that at least most items in that page are actually specified by NEC.

- Don Klipstein ( [e-mail])

[Don Klipstein]

Since resistance increases with temperature, actual ampacity does not increase much with an increase in temperature rating. And ampacity according to the code does not increase at all.

- Don Klipstein ( [e-mail])

[Doug Miller]

Must be a local code. The NEC specifies minimum requirements for conductor sizes, but has no requirement I'm aware of that all conductors on a circuit be the same size.

[Doug Miller]

The temperature rating of a conductor depends on its *insulation*, not the conductor itself. Ampacity *does* increase substantially with an increase in temperature rating, due to the ability of the insulation to withstand a higher conductor temperature.

Example: for copper wire, #8 TW has an ampacity of 40 amps; #8 THHN has an ampacity of 55 amps.

Another example: #18 copper wire is permitted to carry 14 amps, IF it has 90 deg C insulation (e.g. THHN or THHW).

This simply is not true. See NEC Table 310.16 for abundant proof that the Code absolutely does recognize increased ampacity for increased temperature ratings.

[Chris Friesen]

I'm going to have to disagree with that.

For simplicity, look at the "single conductor in free air" tables. (The other tables show it too, just the absolute values are lower.)

With 60-90C rated insulation, a #14 wire is rated for 20A. With

110-125C rated insulation, that same size wire is rated for 40A. If you go up to 200C insulation, you can put 45A through it.

Chris

[Steve Barker LT]

No, he said he needed 16 feet. That's $8. You can buy it by the foot also.

[Don Klipstein]

This sounds to me specific to appliance cords, as opposed to romex.

- Don Klipstein ( [e-mail])

[Don Klipstein]

Somehow, I suspect that upgrading from 110 or 125 C insulation to 200 C insulation only improving ampacity from 40 to 45 amps supports my point!

Meanwhile, also consider that wiring in a building is usually not single conductor in free air, but 2 at least current-carrying conductors close to each other and heating each other up with a sheath around them and the environment outside the sheath usually not being "free air".

Add to this the fact that extra high temperature rating wire is used more where ambient temperature is higher, and I see good reason for AWG 14 romex to be only allowed by code to be used in circuits up to 15 amps regardless of temperature rating.

- Don Klipstein ( [e-mail])

[Doug Miller]

Nope, wrong again. It applies to *all* premises wiring covered by the NEC. There's a lot more than just "romex" involved.

Like I said... See NEC Table 310.16

[Doug Miller]

Quite the opposite: it clearly contradicts your assertion that it "does not increase at all". And, of course, the difference between 20A at 60 deg and 40A at 125 deg makes that contradiction even more clear.

That was just an example -- and maybe not a real good one. But it does show that (not to put too fine a point on it) you don't know what you're talking about when you say that "ampacity according to the code does not increase at all".

That's just not true.

See NEC Table 310.16 for abundant proof that the ampacity of a conductor -- ANY conductor, ANY size -- absolutely DOES increase with increasing temperature rating of the insulation.

That's a completely separate issue from the ampacity of the wire, which Code specifies as being, for example, 25A with THHN insulation. In a separate article, Code limits the overcurrent protection for 14 and 12 ga conductors to

15 and 20 amps, respectively, despite their having a higher ampacity.

[gfretwell]

This whole issue really doesn't have anything to do with the ampacity of the wire. 310.16 says #14 is good for 20a at 60c,. This is really a

240.4(D) issue which builds the "80% rule" into the code for "small conductors". I agree 100% it is a code violation but since a single lampholder is a fixed load of 250w or less I can't see this as being the worst violation I have seen and I wouldn't lose any sleep over it. If he later put a receptacle up there he would be moving into that "uncontrolled load" territory 240.4(D) was written for. It forces the 80% limit with a lower rated breaker than the wire ampacity can support and he is losing that protection