Question about light fixture - 60 / 90 degree wiring

[DooD]

Bought a house last year,one of the first things i did was check all the light fixtures in the house to make sure there were not 100w bulbs in the 60w max fixtures. Of course there were. So fast forward a year and the hallway light is blinking. so i remove the fixture and the wire leads from the socket are dark and overheated looking and generally not safe looking(i suppose from however long the 100w bulb was in there) So i go the home depot and the wife picks out a fixture, single bulb 60w max. So i open the box and see a tag on the wires that there is a warning to only use with 90 degree wiring. Never have i come across this before. So, i go up into the attic and check the wires and they are marked NM and not NM-B.

First question. Am i correct in assuming that wire marked with only NM is 60 degree wire.

Second question. Why is it that this new single 60w max bulb fixture i bought that is labeled use only with 90 degree wiring, generates more heat than other single 60w max bulb fixtures and requires that it be used with minimum 90 degree wiring.

Thanks for any and all responses.

Billy

[Dennis J Sunday]

Look for the letters NMB on the jacket of the wire. The NM means nonmetallic sheath cable (Romex) and the B suffix means that the cable's conductors are rated for a maximum operating temperature of 90°C 194°F. We can assume that wiring made prior to 1984, without the B suffix, is rated at 60°C 140°F. This is the type of wiring found in most older homes that were built before

1982.

Newer light fixtures require that the temperature rating of the wire feeding these fixtures be at least 90 degrees C. This is the temperature rating for these light fixtures. It's important that the temperature rating for the wiring feeding these fixtures match or exceed the rating for the fixture. If the temperature rating of the wiring is lower than the 90 degrees C. required, the insulation around it becomes brittle and may break away. This allows arcing between bare wires, which causes heat that melts the fixture and could be a fire hazard.

[HerHusband]

Billy,

Judging by all the lights we recently purchased, this seems to be the standard these days. Fortunately, the higher temp NM-B wire seems to be the standard too.

If the wire does not have the "B", it's most likely the older low temp wire.

The easy solution is to mount a junction box a couple of feet away in the attic. Disconnect the low temp wire from the light fixture and reroute it to the junction box. Then run a short section of the newer high temp wire from the junction box to your light fixture. Make your connections in the junction box, install a blank cover, then wire up the new light fixture as you normally would.

Anthony

[Toller]

My wiring is NM from 1982, but the fixtures are all 1982 also. No temperature problems then? Right?

[donald girod]

It is very unlikely that lighting fixtures today generate more heat than lighting fixtures of yesteryear. However, because of charred wire problems such as you describe, and just general experience, they decided to increase the required rating on temperature resistance for wiring insulation. One could reason, "in order to be safe, I'll just find an old 1982 fixture at a garage sale and use it with the old 1982 wiring, and it should be just fine". A moment's thought shows that this can't possibly make sense--if the problem is that the old wiring was getting damaged by fixtures putting out more heat than the wire could stand, and thus the industry decided to increase the heat rating on the insulation, why would they then permit fixtures to be made which put out even more heat than the ones which were burning up the old insulation????

The new fixtures probably produce LESS damaging heat than the old ones and would be at least as safe to install as an old one. On the other hand, if you already have damaged wire at the box, it makes sense to replace it if possible with higher-rated wire. A junction box in the attic is a good solution. When this happens in a location where you can't get at the wiring from above, it is not as pleasant to fix things, and may require a lot of drywall patching.

[Mark or Sue]

Yes.

I don't think it does, and it is probably better insulated than the older fixtures. There is just more awareness of the problem now as 30 years of baking wires has caused problems. How many of these problems were caused by 100W lamps in 60W fixtures I don't know.

There is one more thing to consider. In the 60's wires were typically run to the ceiling box and then branched "octopus" style to the receptacles. This means that all the current in the receptacle circuits flowed through the wires in that hot light fixture box. This compounds the heat problem.

While not specifically legal, I use the following rule. If the light fixture only has a cable for that light fixture, or perhaps two cables and the second ONLY goes to another light fixture, then I'll use the older 60C wire on that fixture. If you have receptacles downstream of that light fixture, then I won't do it. Another option is to buy a slightly larger fixture that will take a single 75W or two 75W lamps, but use 60W lamps in them.

Others have mentioned the porper solution, which is to run a short segment of NM-B to that light fixture. However, that can be a lot of work and desruction depending on the access you have to the light fixtures and the other wires, or you willingness to have a blank box cover on the ceiling near the light fixture.

-- Mark Kent, WA

[Jeff Wisnia]

Can you fit a CF (compact flourescent) in that fixture? They put out a LOT less heat for the same lumens.

If a CF fits inside, and you want to be anal about being sure it is OK, you could jam an oven or candy thermometer inside the fixture and see how hot it gets. If it's less than 60 C you should be home free if you stick your own label on the inside that reads "Maximum XX Watt - Compact Flourescent Only."

Just my .02

Jeff

[Eric Tonks]

It is interesting that 90 degree wire was only mandated in 1982. Here in Canada, I was building my house in 1970, and it was just then that cable was mandated to be 90 degree for ceiling light fixtures.

Here cable is labelled NMD-7 (Non Metallic Dry use) for 90 degree use. Previously the 60 degree cable was labelled NMD-3.

Canadian electrical standards have in many areas been more stringent than the US standards. Ground wires and 3 prong plugs have been the standard since early 1960's.

The labelling of ALL new fixtures for 90 degree cable is mostly "lawyer talk" to protect the manufacturers and lawmakers for lawsuits. The new fixtures generate the same heat and they always did for the same bulb size. Keep your bulb size to 60 watts and you should be OK until you decide to rewire your entire house. Just watch out for and repair any crumbling toasted insulation on old wires.

[Michael Daly]

Not just in electrical - structural building codes are the same. One of the reasons is that Canada has a more centralized authority (used to be called NRC) that covered a lot of code standards. In the US, lots of state authorities had local jurisdiction but there was no national authority with clout comparable to the NRC and others. As a result, the Canadians were able to get national standards in place quickly compared to the US. OTOH, states like California could put together structural codes for earthquake that were several years ahead of Canadian standards, since they were in full control of their own jurisdiction (and, in the case of earthquake, motivated).

Over time, all the standards tend to move to the same level of stringency.

One curious thing is that this seems opposite to the way the governments are set up. The US, being a union, has weak states and strong central gov't. Canada, being a confederacy, has strong provincial governments and a relatively weaker federal gov't. Yet the code authorities operate in reverse.

Mike (whose grad research added one sentence to the Canadian building codes back in the '70s)

[DooD]

Thanks everyone for the replys. So, i suppose it is safe to use this fixture. and i may as a few suggested add the junction box and then go to the fixture with some 90C wire. But my question on that is(this is just in general, not specifically to my fixture and wiring situation) does the heat not generate down the length of the wire, or is it just concentrated at and close to the fixture itself? I can go that route as this is in an easy place to get to, it is a hallway light with the attic stairs right there at it. Must add that on this same circuit is one plug in one bedroom and all the plugs in the master bedroom. Also the wires to the fixture look fine, all of that looks really good. It was just the little pigtail leads from the fixture itself that were darkened and brittle and coming apart were they connect to the socket. Everything else appears to be good. We plan to rewire one day, as we have a breaker system in the house now that one person i talked to called them "obsolete" . The Federated (believe that is the name) breakers that i can only get from one place in town and they is pricey. any ways, i tried to touch on everything here in one post in response to everyone so as not to make a bunch of little posts saying the same thing. Again thanks everyone. I appreciate all the info.

Billy

[HerHusband]

Billy,

The heat is from the light bulbs, not the electrical current. I suppose a little heat will travel down the electrical wire by conductance, but that is going to very minimal. Touch a light bulb that has been on a while, and you'll know where the heat is coming from... Ha. Ha.

Even if the fixture had two light bulbs, you're only looking at 120-200 watts or so. That's only a small fraction of the capacity of typical 14 gauge wire.

In our house, we replaced the bulbs with compact fluorescents. About 25 watts instead of 200 watts, very little heat output, and more light as well. Only downside is the additional cost, but then we haven't had to replace a bulb since we switched over.

Anthony