Replacing Wall Fixt. Needs 90C Wiring - How to tell?


Old 05-17-04, 05:20 PM
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Question Replacing Wall Fixt. Needs 90C Wiring - How to tell?

Hello. I'm replacing a wall fixture above the mirror in the bathroom.

The new one has two 150w halogens (300w total) and, unbeknownst to me before it arrived, requires 90C wiring.


- How can I determine whether 90C wiring is already in place? The home was built in 1974 and judging from the old/existing light fixture (incandescent globes), is probably still original

- If 90C wiring isn't there, is it possible to use smaller bulbs (e.g. 100w) instead and be safe?

I'm disinclined to rewire, so if this light isn't possible to use safely, I'll just return it and find one that doesn't require 90C.

Thanks in advance for any help you can offer!
Old 05-17-04, 08:57 PM
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90 degree wiring only started to be used around 1985 or 87.

If you have non-metallic cable you could look for it to say NM-B on exposed cable near your panel. Without the -B you have 60 degree wiring.

No you cannot just use smaller bulbs. This would still be a Code violation as you are not using the product as designed.
Old 05-17-04, 09:32 PM
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Thanks for the quick reply. I'll pull the old fixture tomorrow and check the cable for the markings. I'm assuming the news will be unfavorable, so I guess my options are:

- have an electriction upgrade the wiring to 90C to accomodate the fixture
- get a different fixture

I'm inclined to do the latter ($ issue), so here's a followup question if you don't mind:

Is the requirement for 90C wiring based on the type of lighting (halogen vs. incandescent) or the total wattage of the fixture itself? Or something different?

There was no indication on the outside of the packaging that 90C was required for this particular one...just a note in the installation instructions. I'd like to narrow the search to a viable fixture if there is a rule-of-thumb. For example, should I be looking only at fixtures using LESS than a certain wattage or be avoiding halogens, etc, to be able to safely use the existing wiring?

Thanks again!
Old 05-17-04, 09:34 PM
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Conforming to the 90-degree requirement isn't usually too difficult. You only need the last couple of feet to be 90-degree wire. This can usually be done by installing an extra box a couple of feet away, and running NM-B between the boxes. Both boxes must remain permanently accessible. If there is an attic above this room, it can be accessible from the attic. If there is no attic, you'll need a blank cover plate on the extra box.

Or you can replace the cable back to the nearest existing box.

Or you could just buy a different fixture. Not all of them require 90-degree wire.
Old 05-17-04, 09:44 PM
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Many fixtures, both incandescent and halogen, require 90-degree wire these days. It depends on the design of the fixtures. The fixtures that do not require 90-degree wire are usually those that hold the bulb some distance away from the wall or ceiling.

Alas, it is all too frequent to have warnings and limitations inside the box that aren't evident from the outside. Companies are reluctant to put anything on the box that might cause you not to buy it. That's why I always open up the boxes and read the directions in the store before I buy it. If the store doesn't like it, they should insist the manufacturers put essential information on the box. Another example of this is appliances, such as air conditioners and space heaters, that proudly say "120 volts" on the package, but don't mention how many amps. It's only when you open the box that you find out that they will blow your circuit if you plug them in.
Old 05-17-04, 10:09 PM
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Thanks for the additional info, John.

So, the 90 degree requirement is a function of both the fixture's current draw/wattage (which creates heat in the wiring, I suppose) and the proximity of the bulbs to the wall/ceiling (ambient heat)? If the 90C "rule" can be satisfied w/a 2-foot final run, then is the proximity of the bulbs to the wall/ceiling a greater factor? If that's the case, would it be fair to say that for the same wattage, an incandescent is les likely to require 90C wiring than a halogen, since the incan tends to burn cooler? And a flourescent would probably be least likely to require the 90C wiring (though that's out for the bathroom as it's above the vanity).

Always interesting to learn! Just thinking out loud so I understand more

I guess I'll be cracking boxes @ the store depending on my findings behind the current fixture. This particular one was an internet order. Ah well, It was nice to save 50% for a day
Old 05-18-04, 04:19 PM
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Just NM on the wiring. Returned the fixture and picked up an alternative one. FWIW the new one uses incan's rather than halogen (all the halogen wall fixtures @ a couple of local stores required 90 degree wiring).

Thanks again for the help. I'll be back in a few weeks when I try to replace kitchen overhead flourescents (in a "dropped" ceiling) with recessed lighting. Now I know to look for ones compatible w/existing wiring along with IC. Off to surf for other tips re: that project in the meantime.

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