20 gauge wire in 120volt light fixtures
| Posted in Energy, Heating & Insulation on
Just finished replacing a pendant light fixture. The pendant was suspended by the cord and held in place with a set screw. As the pendant head moved, the set screw cut into the cord and shorted the hot to the neutral. The wire totally melted and the glass pendant crashed to the ground. The wire size was approximately 20 gauge.
Just wondering why light fixtures are allowed to have 16 gauge and thinner wire in them when the house wiring by code has to be 14 gauge or bigger. (on a 15 amp circuit). It seems to me that light fixtures that have thinner wire should be required to be fused or have a built in circuit breaker.
Edited 12/7/2003 10:01:28 PM ET by Unisaw
Replies
Because the thickness is relative--over the length of the wire. Longer wires must be thicker. Thinner wires must be shorter. 20 ga. is pushing it, however.
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934
Boris--
I'm gonna ask you to educate me. Seems to me that once you connect the fixture to the house run of 14-2 NMD or whatever, then the wiring inside the fixture becomes part of the entire run from the power source; hence no matter if it's only 12" long inside the fixture, it may now be up to 30 meters back to the hot box.
What's wrong with this reasoning, if anything?
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
He is referring to the voltage drop.
I understand voltage drop in a long run. What I don't understand is how the section of wire that came with the fixture can be considered a separate short run once it's electrically and physically connected to the 30-meters or whatever of house wire. Seems to me that electrically, it's all one run once the connection is made. So the controlling parameters on that run would have to be based on the total length of run, not on the 12" or so inside the fixture box.
???
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
Yes you are absolutely right that it is one run from the breaker to the lamp. I think what he was referring to was the fact that since it was the end of the run and it was a short length, the wire size could drop a bit without much consequence.
If you would let me explain it in plumbing terms, it's like your main supply lines are 3/4 and the branches going to the fixtures are 1/2.
See if he'll respond so we don't have to keep guessing.
Snow your way?
Yup. This was taken Saturday afternoon at our local cross country ski centre. That's my little guy; 5 years old, on his third season of XC ski already. Just graduated him to 140cm skis. He flies!
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
You must feel really proud.
Mine aren't that cute anymore, 25 and 23.
When he's a hundred and forty, he'll still be my little boy--but he's already my big man, and has been since he grabbed my finger in the delivery room and hung on tight....Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
Ok I was in Sutton on Saturday and it was just starting to snow. We got 18 inches by Sunday. Took my Dad and I two hours to do his driveway and the neighbours. Went home on Sunday afternoon and Montreal had only 2 inches.
Where in La Belle Provence are you?Ham and Eggs are a days work for the chicken but a life long commitment for the pig
Disneyland North (also known as Intrawestville....)
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
Lenght does not have anything to do with it. He was wrong.
The reason that it is allowed is that you have a limited load. Even with a multiple bulb fixture it hard to get more than 300 watts load.
Also a section in NEC that allows current based on wire temperature rating.
Have seen 18 AWG used for 30 A 3 phase circutis (only a few inches) and 20 AWG used for 20 A circuits. In both cases the conductors used as fail safe fuses in missile systems. 260C rated wire - nickel plated copper conductors, teflon insul.
Betcha that there Chinese fixture does not have 260 C wire.
Different set of rules. The fixture wires are assumed to be enclosed within the fixture or junction box and so not subject to the vagaries and dangers associated with being enclosed inside a wall or exposed to flammable materials. For the most part the assumptions are justified. Those fires, thankfully most were minor, I have seen with fixtures would not have been avoided had they used a larger gauge of conductor.
4lorn1 and Boris, thanks for the info. It just seems that we spend so much time making sure the house wiring is done right, just to install light fixtures that are sub-standard. Even some of the UL approved fixtures seem dangerous.
Just re-read NEC Article 402 on fixture wires. 18 gauge is the smallest allowed. Allowable ampacity is 6amps.
Nothing substandard about them as long as they have a genuine UL listing. Only very rarely do I see truly substandard units. Saw some at the flea market, alongside the fake Rolex watches, that carried no UL sticker and one that had a fake sticker. UL stickers are usually not misspelled.
Some may not meet your standards, largely because I don't think you understand what is required and why, but they are designed to be safe under the conditions of use and to not start fires. In this they do quite well. The only fires that I have seen associated with fixtures typically because of massive overlamping or because of a failed thermal overload, the light had been blinking on and off for weeks, in a 8' florescent fixture not because the wire size was too fine.
18ga wires are pretty standard to many small fixtures. I don't think any great, possibly any, gains in safety would be had if we required the fixtures be wired in #12. It is not a problem.
If you wish to militate for safer fixtures there are far more pressing improvements to be had than demanding larger wire sizes. Many standard Edison sockets are IMHO substandard. Banning the cheap bakelite versions. Eliminating any with an aluminum shell and/or aluminum rivets holding them together would also save a lot of trouble. Porcelain sockets with brass, plated or not, shells and screws instead of rivets, particularly aluminum rivets, should be the minimum standard.
Then again I, unless forced by a specification or a HO, don't buy cheap units with cheap sockets. The same goes for quartz tube floods. Most burn so hot they destroy the fixture as a matter of course. The bulbs seldom last more than a few weeks if used regularly. By the fourth or fifth tube the terminals are shot. Necessitating jury rigging or replacement or the entire fixture. I steer my customers to florescent floods, much more efficient and each bulb lasts for years, or other options like HPS.
But then again electrical standard are not designed to provide efficient and useful fixtures. As far as regulations go as long as it doesn't start a fire when it goes bad it matters little if it just fails to work a week after being installed.
The perfect example is the approval of the modular devices, box and device in one and you don't even need to strip the wires, common to many mobile homes. I have never seen a fire caused by a modular device that could not have gone the same way with a standard unit. These puppies are not reliable but they seldom fail catastrophically. Saw one blow off its side but I've also seen a loose connection and a heavy load melt the box from around a standard receptacle. Generally they just fail to work.
Any electricians with experience, suffering, with this trash is more than welcome to wade in with an opinion of these devices but this is a family forum so they may have to restrain their enthusiasm a bit. Only reason I know to like them is that they guarantee a steady run of service calls.
4lorn1,
I was disappointed that the fixture failed. I installed it in 1998, and purchased it from a reputable supplier. I now realize that the label read, "conforms to UL" not UL listed.
My goal is not to militate (yes, I had to look up the meaning) the use of larger wire size, but to understand why the fixture failed. The more I review it, the more it seems that the set screw that tightened against the cord was the culprit.
So I guess my mistake was being deceived by "conforms to UL" verses "UL listed".
Might not have helped. UL just tries to keep it from causing a fire or electrocuting you when it fails. I assume it didn't cause a fire. Unless you typing from the hereafter I take it a read that your not dead.
The other thing is 14 gauge is rated for 15A circuits but the light fixture by itself is not going to draw 15A and the current to the fixture is the only current going through the wire. The fixture is rated for lamp wattage so they would know exactly what maximun load the wire is going to carry.
TOMCHARK,
I question designing the light fixture around the lamp load. We don't design house circuits around the load, but around the smallest wire size. If a dead short occurs in the light fixture the load will be as high as the circuit breaker protecting the circuit.
Dear Unisaw: Just keep in mind that the wiring in the light fixture is of the gauge (i.e. #20 ga.) designed to carry the wattage for that light only. House wiring ( in this case #14ga./#16ga.) is designed to carry wattage not only to the light in question BUT also to all additional outlets on the same circuit. Hope this helps. My policy in wiring a circuit is to use #12ga. wiring as wiring is relatively cheep compared to installation and you improve capacity by approx 30%. This may help later on if you require more capacity and the drywall has been installed. Hope this helps. Harry