I am installing new lights in a 1950s house. The lights have the warning regarding using 90°C rated wire (NM-B). The house is obviously not wired to that standard. If I install the new lights, do I need to wire NM-B all the way back to the breaker? (I guess the sub-question is: is it the light itself producing the heat requiring the NM-B (in which case a short run of NM-B away from the ligth will suffice) or is it the electrical draw itself in which case the whole run should be NM-B?) Thanks in advance for any help.
If the instructions say "use 90 degree wire," that is a real hint that the fixture fot over 75 degrees using the largest permitted bulb, installed per instructions. There is a lot of room for "professional judgement" as to just how far that hot zone will extend, depending upon the installation. What is not so obvious is that the fixture will also affect other thing that are close to it. As an example, I would say that in the case of a fluorescent fixture in a drop ceiling, the wires only need to be 90 degree rated to the end of the whip. For a recessed can in an uninsulated confined space, I'd want all wires in that space rated. For a lampholder with a PAR or halogen lamp 'poked through' an outside wall, only the wires to the fixture need be rated. I think these examples show how the entire installation is relevant. The instructions do not, however, imply that you need to run 90 degree wire all the way to the panel.
One solution I have (reluctantly) used is to install high-temperature sleeving. It is manufactured as electrical insulation and comes in a variety of materials and temperature ratings. I read about it in a book, and decided that, in an emergency, it would be acceptable. The other solution is a "throw away box..." Pry out the existing box, splice a short piece of new cable, and push the old box aside (throw it away) to make room for the new one.
I recently spoke to a UL representative about this. He said that the heat from the fixture is the reason for the warning. He also said that this is a concern for them because the fear of fire in the 'old' wiring is very clear. He suggested rewiring, I know that is not always easy, but it is easier (mentally) than rewiring after the fire. My suggestion is, do not bury old wire in the ceiling or wall to make the job easier, in the long term it could become a big problem.
It is the heat from the light fixture that you have to worry about, not the heat from the current flowing in the wires (assuming the wires are sized large enough). See 410.67 for recessed fixtures, you can slice the wires in an outlet box at least one foot away from the fixture. Also see 410.11 and 410.33. At any rate, you shouldn't have to run new wire back to the breaker box.
410.11 noted Steve66, especially the wording in the 1st sentence.....
410.11 Temperature Limit of Conductors in Outlet Boxes. Luminaires (fixtures) shall be of such construction or installed so that the conductors in outlet boxes shall not be subjected to temperatures greater than that for which the conductors are rated. Branch-circuit wiring, other than 2-wire or multiwire branch circuits supplying power to luminaires (fixtures) connected together, shall not be passed through an outlet box that is an integral part of a luminaire (fixture) unless the luminaire (fixture) is identified for through-wiring.
FPN:See 410.32 for wiring supplying power to fixtures connected together. Branch-circuit conductors run to a lighting outlet box are not permitted to be subjected to higher temperatures than those temperatures for which they are rated. For example, conductors are rated 75°C and are to supply a ceiling outlet box for the connection of a surface-mounted luminaire or attached outlet box of a recessed luminaire. The design and installation of the luminaire should be such that the heat of the lamps does not subject the conductors to a greater temperature than 75°C. These types of luminaire are listed by Underwriters Laboratories Inc. based on a heat-contributing factor of the supply conductors of not more than the maximum permitted lamp wattage of the luminaire. Exhibit 410.2 illustrates recessed luminaires listed by Underwriters Laboratories Inc. for one set of supply conductors, and Exhibit 410.3 illustrates luminaires listed for a feed-through installation.
so by virtue of the small print disclaimer, the majority of luminaires marketed are done so unethically.
[This message has been edited by sparky (edited 06-26-2003).]
you see Steve66, there is no clear answer that we, as trades(people) can offer , especially inclusive of every application.
This has been a perenial Q on the DIY, as well as professional forums ad nasuem.
It serves as example for the manufacture's to pass on liability for cheesy products, leaving the trade with obscure codes , indifferent testing lab advice, and fine print all of 'interpetational' caliber.
Unless of course, rewiring, sheetrockers, mudders, painters are recommended by the majority here ( as well as that big orange place) et all ......
Yet have no doubt, if there was an AFLI (arc fault luminare interupter) the trade mags would be full of code gurus and manuf. reps touting the evils of those cheap ignitable's marketed....
~Steve aka sparky
[This message has been edited by sparky (edited 06-27-2003).]
Ahh, for the bad old days when a light fixture could be screwed to a box (why take the time to fiddle with those extra parts?) and one could put in the bulb(s) large enough for Grandma's dim eyes. . . .
Steve, there is another choice: limit ones selection of new luminaires to those that suit the situation.
I know that this requires the customer to be educated about the specific limitations of the specific outlet in his dwelling, but, really, it's not our fault that the wiring in that j-box has been shown to degrade in excess heat. The old R, RH, T, TW, NM, etc. was designed within the knowledge of the time, as were the fixtures. In the pre-1985 home one accepts, by ownership, the liability of the older infrastructure along with its charm and character.