We recently purchased a fixer-upper 1950’s cape cod with many, many challenges. While renovating the bathroom we removed the old overhead light fixture (rusted and broken) and promptly bought a new one to replace it. The new fixture has a warning that says the fixture can only be used with 90 degree wiring, not widely used prior to 1985. What is 90 degree wire? Should I replace all of the wire (no way!)? Should I replace the wire from the fixture to the switch or all the way back to the breaker box?
This site has an answer and explanation: http://www.findarticles.com/cf_dls/m1080/2_50/59086076/p1/article.jhtml
The wire is rated to withstand temperatures of 90 degrees C. If I understand correctly, it would only be needed in and near the fixture where there could be significant heat build-up. Perhaps an electrician could confirm that.
Actually, it’s the insulation that’s rated, not the wire. If you are doing the installation yourself, you’ll be fine with running 90 degree wire back to the first junction box. If the city is going to inspect it, all bets are off. We recently had an inspector come in on one of our larger projects and insist that we had to replace all of the 60 degree wiring with 90. Makes no sense whatsoever, but it’s tough to argue with them.
Thank you both - excellent information that makes perfect sense.
I will be running the wire myself - I already bought ROMEX for the job. This will be my 3rd (fingers crossed) electrical project and so far I haven’t Wyle E. Coyoted myself.
If the insulation on the wires in the cieling box appear to be cracked or brittle then you need to address the issue (probably replace the wiring). If the wires are OK then I would opt for some 90 degrees C shrink tubing and slide that over the wires. Also, the good 3M 33+ tape is rated at 90 degrees C.
However, you seem to be ready to replace the wires to the nearest box or the switch so I would continue with that project.
The concern is that the lamps in the fixture will heat up the insulation and break it down over time - resulting in brittle or cracked insulation. Your wire nuts (wire connectors) need to be rated for 90 degrees C also.
It isn`t necessary to replace ALL the wiring at this time since the only part of the wire that is affected are the parts exposed to the heat of the lamps inside the junction box. You would only need to replace all the wiring back to the breaker if you intend to change the amperage of the circuit (15 amps to 20 amps or such) or if there is damage to the rest of the wiring on that circuit due to some other type of overloading and subsequent heat buildup throughout the conductor.
Come back if you have any other Q`s regarding the details of your project. 
We’ve been sidetracked by a few more important projects and in the meantime my father-in-law suggested using a lower watt bulb in the fixture to reduce heat buildup. I was thinking I could use a fluorescent bulb (one of the fluorescents that screw into incandescent sockets) and that would produce very little heat. Is this acceptable instead of replacing all of the wiring?
Incidentally, we found that the wiring continues from the overhead light to points unknown, so replacement of the wiring is a much bigger job than anticipated and we’d like to avoid it, if possible.
Chunky
No that wouldn’t be acceptable. There is nothing to prevent anyone else from putting in a bulb compliant with the rating of the fixture, so it’s not allowed. I would go with the heat shrink tubing (but I don’t know if your inspector would agree.)
As others wrote, high temp electrical tape or tubing is much better, legal, and trivial to do.
If for some reason you have to replace the wiring at the fixture, you don’t (always) have to go all the way back. If the space above the fixture is accessible (in an attic, for instance), then you can place a junction box a few feet away from the fixture, run romex to the fixture, and tie into the old wiring (with wirenuts) at the junction box. Not the greatest fix, but better than nothing and legal.
Thanks again - I’ll look for the heat shrink tubing.