15 gage wire on 20 amp circuit

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There are some cases where you can use smaller wire for a subbranch than the branch breaker permits[1], but sticking a lightbulb via 14ga on a 20A residential circuit ain't one of them.
The rationale being that it's okay to finesse a few "special purpose" circuits (ie: high amperage) that are unlikely to be futzed with and are unlikely to have faults.
But not with an ordinary 15A or 20A circuit, because 5 years down the road the DIYer is going to be wiring an outlet to supply a 2000W heater, or he'll throw the electric razor in a fit of anger, and the light fixture will fault such that it conducts 19A over a 14ga circuit and won't trip the breaker.
[1] Mostly to do with motors, tho, downsized short branches for separate cooktop/oven combinations are also permitted in some circumstances, and would be just about the only time you'd see that in residences. Sometimes known as the "25' rule". [details vary from locale to locale]
--
Chris Lewis, Una confibula non set est
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Usernet User wrote:

Some 14 gauge wire can handle 20A if it is in conduit instead of made up into cable, but the electric code doesn't let you do it and I don't know why. Not enough margin for error? You're probably using NM-B or armored cable, so it's a moot point. The 14 gauge cable is only rated for 15 amps. You would think you could use 14 gauge wire for a lighting tap on a 20A circuit, but you can't because you don't know if some idiot will later extend that tap to several more lights and a ceiling bathroom heater and exhaust fan, and 2 outlets in the next room ;-)
The *fixture* wires can be 16 or 18 gauge (probably 105 degrees wire) because they can't be extended to another outlet. If you look closely, the fixture has a UL or CSA label somewhere, and the fixture wires are part of the fixture. Someone has tested it to make sure the wire is big enough.
Best regards, Bob
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zxcvbob wrote:

If I remember correctly, that in NOT in a conduit, but in free air and if I remember correctly that is acceptable via code. However, my memory is far from great.
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Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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That wouldn't be conduit. Especially plastic. Remember the conduit fill tables in the code books are for ampacity _DE_rating.
Free air melt point for bare 18ga, 25C ambient, is 100A. Whereas its inwall safe rating is around 5A.
Environmental considerations and safety margins play a vastly bigger role than most people think. Wire sizes in electronics and transformers, for example, follow different rules.
There wouldn't be many times that a 14ga wire would be acceptable at 20A _inside_ a house if it's acceptable _anywhere_. "Free air" doesn't really apply enough indoors to be worth considering.
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Chris Lewis, Una confibula non set est
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Usernet User wrote:

> Oops. I meant 14 gauge wire on a 20amp circuit. > > There is only one 20 receptable on the bathroom circuit. The only use > of that is probably just hair dryer. So adding a 100W light should be > no problem. > > Now if the bulp is on a lamp, you might be able to use a 18 gauge wire > (to connect to an outlet). But when it is ceiling light, you have to make > the wire 12 gauge. Why? > > UU >
If condensation from the shower forms on the bulb and it shatters from the uneven cooling following which the filament holders short out drawing excessive current do you want the breaker to open or that undersized fourteen gauge wire to act as a fuse and burn up inside your wall or ceiling?
What is so dam difficult about using twelve gauge wire? Are you trying to save a buck, as in one dollar or less, by using the undersized cable? The reason that the lamp cord can be so much smaller is that it's entire length is available for inspection and if you have the brains God gives an idiot you will repair it if it starts to deteriorate. You have no way of watching over the condition of a cable that you install in a wall or ceiling that is the breakers job.
I was called out in the middle of the night by an elderly women who had a light in her basement ceiling that wouldn't go off. When I got to the house the light turned out to be a piece of lamp cord that was glowing in the dark. It had been used to supply an outlet that when it was installed was only used for a reading lamp or table radio. It was now supplying an air conditioner because the elderly occupant didn't know what her deceased husband had done. Right now you plan on a single bulb. The next occupant may convert that outlet to a radiant ceiling heater that draws between one and two thousand watts. If the cable is twelve gauge the breaker will open on the overload and no damage will occur. If the cable is fourteen gauge the cable could short out and start a fire.
You don't like our answers and want someone to bless your half baked installation. Fine. It's your families lives your risking do what you please. I'm an electrician but I'm also a volunteer fire fighter. I have carried out people who were burned beyond recognition and little children that looked like they were just asleep. What they all had in common was being dead. One of every ten structure fires in the US is of electrical origin. USE THE NUMBER TWELVE AMERICAN WIRE GAUGE CABLE FOR THE LOVE OF ALL THAT'S HOLY. Yes I was screaming at you. -- Tom Horne
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easy there, Tom...

make
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Chuck wrote:

Tom has a right to be a little uneasy. A lot of fires are started by someone who cheats the code. People do die. It is just totally foolish to cheat the code because you think you know better. The code is NOT a guide it is a rule and should be treated as such.
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Joseph E. Meehan

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I didn't think he yelled loud enough ;-)
His yelling may better have been aimed at some of those people who were telling him it was okay. I just hope he saves that rant for reuse.
Can I borrow it for the electrical wiring FAQ Tom?
--
Chris Lewis, Una confibula non set est
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Do you have a wiring FAQ? I'd like to see it.
bmason at accesswave dot ca if you could please send it, thanks.
- Bill

by
to
guide
telling
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check out www.homewiringandmore.com
This has more on wiring than any place I've ever seen
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This is one of the canonical places that get updated as it's reposted:
http://www.faqs.org/faqs/electrical-wiring/part1/preamble.html http://www.faqs.org/faqs/electrical-wiring/part2/preamble.html
You can find it on google quite easily, but many of those don't automatically update.
--
Chris Lewis, Una confibula non set est
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