Electricians... household wiring rating question

I’m getting ready to install a new lighting fixture in my kitchen, it is a flush mounted unit with a 55watt fluorescent bulb. The fixture there now is a hanging unit with a 100watt incandescent, so the wattage shouldn’t be a problem.

My question regards a big warning on the main section of the new fixture that says “MIN 90[SUP]o[/SUP]C SUPPLY CONDUCTORS” with additional warnings about a risk of fire. It also mentioned that “most” dwellings built before 1985 have wire rated 90[sup]o[/sup]C.

My place is a bit on the older side, and is wired with armored cable for that box. Am I OK to put this fixture in, or should I return it and look for a different model?

90 °C is the temperature rating of the fixture. Therefore, it would make sense that the wiring it connects to should have an equal or greater temperature rating.

Why? Because the ballast gets hot. Some of this heat conducts along the copper conductors and into your house wiring. The insulation of your house wiring must be able to withstand this heat. If, for example, a ballast operating at 80 °C was connected to wire rated for 75 °C, the insulation might become brittle and break away (which could cause arcing). A ballast operating at 80 °C connected to wire rated for 90 °C would be O.K.

So let’s assume you have 75 °C wiring in your house. Will your house wiring ever see temperatures above 75 °C if you use this fixture? It’s hard to say, since it depends not only on the fixture/ballast but on the temperature in the attic (which depends on ventilation, insulation, etc.) But why take a chance? Return the fixture and get one rated for 75 °C. If you can’t find one, then I would install four or five feet of 90 °C wiring.

Crafterman probably nailed it. He`s mostly right-on with this stuff.:wink:

Does the wire that comes out of the armored cable have a cloth type cover on it? Or is it the smooth, shiny, insulation?
The cloth (older) insulation may not be rated at 90 degrees C. ( its probably 75 or 60 and its impossible to tell with out stripping back the armor and reading the rating on the wiring)
The newer insulation (THHN) IS rated at 90 degrees C.

You could either get a different fixture or change the ballast out to an electronic ballast. The electronic solid state ballast will accomlish the same thing except they are more efficient and run much cooler. They are also more expensive, hence they dont come in all fixtures from the factory. If you really like the fixture then you could keep it and simply swap out ballasts. Its simple to do and the new ones will come with a wiring diagram, which usually ends up being color for color anyway (hard to screw up). Youll have to get the new ballast from a lighting distributer if the other stores dont stock them.

If you choose to install the current light and aren`t sure of the wires rating I would be worried about insulation breakdown even though it may take years for it to occur.

I’m pretty sure it is the smooth insulation, so I guess I’m ok with it. Thanks for the electronic ballast idea, I’ll probably look into it anyway, just in case. Thanks so much for the info, the maintenance guy didn’t know a darned thing!

One thing you may want to do (as I mentioned in my first post) is buy a few feet of 90 °C cable and wire it between your fixture and older wiring (use wire nuts). It would be very simple and inexpensive. And I’m very confident that, if the fixture was truly operating above 75 °C (which I’m guessing is unlikely), the few feet of 90 °C cable will dissipate enough heat such that your existing wiring will be O.K…

Thanks for the accolades, but I prefer cold hard cash. Please send it to my P.O. Box on my web page at your earliest convenience. :wink:

[sub]Just joking. You’re pretty sharp with this stuff too.[/sub]

Does “am I ok” mean according to the 2002 NEC or according to what some posters think would be safe? Not too sure, but I think the code calls for all the wiring back to the breaker to be rated at the temp rating of the fixture. Let’s say you did as advised above, installed a few feet of hi temp wire and had a fire. If the code says otherwise and you did an improper install, what happens next? (if you live through the fire)
Check the existing wire without making assumptions about it based on shininess. Before changing ballasts, remember that when you modify the fixture, you void the UL listing.
Or…just do as the other posters suggested and you’ll probably be safe. Just never sell the house with all this on record here!

I think the biggest problem with the “buy a few feet of 90 °C cable” idea is that any splice in the wires has to be in a junction box and accessible (that is, you can’t just stick the wire nuts in the ceiling). And if the wire nuts and several feet of wiring are in the junction box adjacent to the light fixture, you’ve pretty much defeated the purpose of the higher temperature wire.

Correctomundo. Ever see a light fixture somewhere and a blank plate a foot or so away? This little dodge involves running a “pigtail” of 90° wire out of the box the fixture is mounted to and making the transition to “regular” temp wiring nearby. Kinda funky looking, but a common retrofit practice as it saves you from having to rip out all the wire between box and switch.

There’s no requirement that all the wire in the circuit needs to be 90° or whatever. Just where it’s hot. The requirement MajorTom is probably thinking of is wire gauge - you can’t use thinner wire on the way back to the breaker. You can, however, use thicker (lower gauge number) wire for a long run back to the panel, but the breaker must be sized to suit the smallest wire and/or the device (lamp, receptacle, etc.)

No, the wiring all the way back to the breaker does not need to be the rating of the fixture.

What Crafterman suggested was to extend* the old wiring from the box to the fixture with the new 90 C. rated wire.
What happens is this; you mount the light fixture but the wires from the box hardly ever reach the wires on the flourescent fixtures. So, you have to make the pigtail extensions with the new wire. Make the splice to the old wire and tuck it inside the box (cover with insulation if desired). Now you only have the new wires running from the splice in the box into the fixture where the heat is. Case closed.
PS, the newer cables that don`t have the cloth insulation are rated at 90 C. (The shiny wires) There really is no other way to describe the wires. You would have to strip back a bunch of the cable in order to read the listing on the insulation.

Finagle Not really. The heat will affect the wires closest to the ballast. The wires in the J-box will be alright as long as the ballast isn`t mounted directly under it (in essence covering the opening).

gotpasswords - Almost correct. You can install 15 amp receptacles on a 20 amp circuit. You can also plug a lamp with 18 guage wire into that circuit too.
What you cant do is put a 20 amp breaker on a circuit with 15 amp wire feeding the branch circuit. The 80 percent rule says that you cant load a circuit continuously at over 80 percent. 80 percent of 20 is 16. 1 amp more than what the 15 amp wiring is rated at. In short, you must always size your breaker according to the feeder size. It doesn`t matter what you have plugged into the ciruit (lamps, receptacles, etc.)
NEC article 210-24 (table) allows a 20 amp branch circuit to have either 15 amp or 20 amp devices installed.
A 15 amp branch circuit may only have 15 amp devices however.

Yea yea, I know that shoving the loose wire nut junctions into the ceiling is not exactly “by the book” according to the NEC. But (in my humble opinion) there’s nothing inherently wrong with it. (That’s what I would do.) If it makes you feel better, I will suggest to Cheesesteak that he put the junctions inside a cheap plastic junction box and throw it up in the ceiling…

Which assumes the existence of a largish hole in ceiling.

Cable joins in the ceiling space outside a junction box violate the double-insulation principles. They really can be:

a) a personal hazard to anyone working in the ceiling space, and
b) a fire hazard.

Whatever. :rolleyes: I guess I’m just an out-of-control maverick when it comes to wiring…


Nothing personal, but its guys like this that make The Milwaukee Saw-Zal a necessity when you cant find the splice that should be in a junction box and end up cutting open the dry wall looking for the rogue splice.:wink:

I went into a house that the homeowner wired himself. He used 10/3 romex to wire EVERYTHING. You can`t fit more than one 10/3 cable into a box comfortably so the guy made all his splices outside of each box and behind the drywall and just brought in the pigtails to the outlets. He had an open hot somewhere and I had to get out the trusty Saw-Zal to find it.