Here is one for you all out there who may not know this. SOme of you prob know this but for the benefit of those that don’t this seems important.
This morning I replaced a ceiling light fixture. HO complained the light just stopped working and when they would touch it the bulb would be hotter than hell and they heard some arcing/frying sounds.
I disassembled the fixture and saw the problem, the individual conductor wire insulation appeared to be sliced or damaged in some way as to expose a small part of it and it appeared it may have been arcing to the ground, I wasn’t sure. As I pulled the conductors out of the box they began making “toothpick snapping” sounds and I looked at the conductors and the conductor insulation was as brittle as a toothpick. If I bent the wire only a slight radius the insulation would just snap and crack or a piece of it would snap off exposing bare wire.
Having never seen this before I theorized that the wire was just old and not built to last they way it is today. This wire was an old form of “romex” in that it had a thick cloth outter insulation around the bundle of wires, but the conductors inside were individually insulated such that it looked like regular NM-B cable and color coded, etc.
Again not having ever witnessed this before I asked my inspector about it. He said it’s not uncommon. He said often times people will put in a higher wattage bulb than the fixture is rated for. The resulting heat “cooks” the wire insulation, dries it out like the Sahara to where it gets brittle like that. Said it’s an extreme fire hazzard and needs to be address immediately (couldn’t agree more).
I never knew this and frankly been guilty a few times myself of using a stronger bulb for more light than the fixture called for. Ignorance is bliss. For anyone else out there who might do that…don’t.
Replies
Shucks ... I saw the title and thought someone had finally found the receipe for that noodle casserole DW makes ... well, she says it's noodles, but they taste like burnt rubber to me.
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
Older wiring had lower temperature ratings, the maximum temperature it can maintain before it starts to melt, harden or deteriorate. Modern NM, romex has THHN insulation rated to 90C. Older NM was only rated at 60C or 75C. If the fixture is designed to be used with higher rated conductors than 75C it is usually marked.
Old wire under modern fixtures, ones that run hotter, can rapidly melt or embrittle the insulation and make a short very likely.
The other side of this is the lamps, bulbs, used. Most fixtures are only rated for use with 60 watt bulbs. Anything heavier will make the fixture run hotter. Massively overlamped fixtures can melt insulation even on modern conductors.
Taken to the extreme they can melt plastic boxes, make the paper that holds drywall brittle and melt the jacket and insulation off cables going into the box. I have seen the ceiling for a radius of a full foot dried out to the point where it fell out after the fixture was removed. I have seen metal boxes get hot enough to char the framing it was nailed to.
With a little luck the romex has enough slack to get the jacket into the box so the undamaged insulation can be used. Worse case you install a new box in the attic and feed a new length of cable into the existing box. If the cable jacket, the plastic sleeve surrounding all the conductors for mechanical protection, is intact, still flexible, and protruding into the box it should be OK.
The jacket must get into the box to prevent the box edge around the entrance hole from rubbing on the insulation around each conductor. If it doesn't, and the insulation on the conductors is still live, removing the cable from the box and wrapping with friction tape can provide a similar, or better, level of mechanical protection.
If only the insulation on the individuals is damaged it can sometimes be replaced with heat shrink tubing. This will not slide off if you use a little Scotchcoat under the tubing. Be sure to overlap a little of the still good insulation with the heat shrink. This is a tricky operation reserved for situations where the area above the box is inaccessible as in some cathedral ceilings or below a second floor.
Lorn, related questions.
Is soldered splice protected by heat shrink tubing a code approved installation?
What is Scotchcoat and how do you apply it.
What heat source do you use to shrink the tubing?
Tom,
4Lorn can answer for himself, but FWIW, I use a painters heat gun on the low setting, an el cheapo model and it's worked great for shrink tubing. But I hold it pretty far away, just far enough that it's able to do the job. Though I've never used it I could've sworn someone once told me a hair dryer will do the job. Prob would, but I'd rather use the heat gun since I useit to remove paint, so I carry one tool, not two.
I have only done the shrinking act once using a hair dryer and yes it worked...really slow, and I had to cover part of the intake to get the heat up. I thought someone might use a pocket butane torch or something.
Once I dismantled a furnace blower motor and found the same thing as you described.
I have used both. Good call. One is a little slower than the other. Blowdrier is also good for starting charcoal. Did this a short ime ago. Really speeds things up. Important when a storm is bearing down.
"Is soldered splice protected by heat shrink tubing a code approved installation?"
Sorry, no. Especially if it is not within an accessible box with a cover. Still not approved in a box but I have seen far worse so if you have done a few, and done them well, I wouldn't run out of the house screaming. For house and fixture wiring wirnuts are pretty much the industry standard. I twist before putting the nut on firmly. Use good quality wirenuts.
You could use crimps, lugs or other methods but, IMHO, all these are harder to get right and certainly take more time and effort than just twisting on a wirenut. No need to reinvent the wheel here.
"What is Scotchcoat and how do you apply it."
Scotchcoat is a painted on coating. It is used to keep moisture out of underground, underwater, splices. Some use it under the tape wrap. Applying the tape while the coating is still soft. More commonly it is painted over a taped splice and onto undamaged insulation a bit to seal any pinholes and provide extra abrasion resistance.
It comes in cans with a brush under the cap similar to PVC cement. As a liquid it is thickish and rust brown. It dries by evaporation to a tough, hard to cut this stuff if laid on thick even with a sharp knife, air and watertight coating. By adding coats you can build up a considerable thickness. Once dried the material is a good insulator and highly resistant to solvents.
In the case I laid out with the heat shrink tubing the Scotchcoat is used only as a glue to keep the tubing from sliding down the wire and exposing the conductor at the other end. I have done this without Scotchcoat and it worked out fine but if I have this chemical handy the extra few seconds spent seems worthwhile. I had a friend that used superglue for a similar effect.
You can buy Scotchcoat in any good electrical supply house but I have seen small cans, I can do a lot of splices with a small 6 oz. can, in home stores. Lowe's, HD, etc. It is handy stuff. I have also used it to patch holes in yellow rain slickers and rubber boots.
"What heat source do you use to shrink the tubing?"
A hairdrier on high will work. This will also speed the drying of Scotchcoat so you can recoat more quickly. A heat gun, a glorified and ballsy hair drier, works a little faster than the hair styling unit. A propane torch, if you use care and a light touch, can work well but don't set the attic on fire. A Bic lighter or Zippo can be used in a pinch. Again use care with the open flame.
A spray bottle full of water, add a few drops of dish soap to allow it to penetrate insulation, makes a cheap and effective, low impact, fire extinguisher when using open flames. Especially in attics. Keep a bigger model or hose handy in case things get out of hand.
Hey 4Lorn, that was really educational, thanks for elaborating so much. I mean, who'd have thunk it? Indeed this wiring is the much older style of "romex." It is 14/2 W/ground but it has that old rayonlike cloth outer "jacket" as insulation but the normal "plastic" like insulation around the individual conductors.
The HO said the unit was very much hotter than normal. In other words she's observed thru the years of cleaning and changing bulbs, etc, that it was hot, but "not as hot as it is was before I called you" as she said.
Anyways, I'm gonna need luck. To replace this wire will be a huge PITA because the area overhead is completely inaccessible. This is a 50's style home. No "attic" but it has "side attics", kinda like dormer attics but very little room and certainly not enough room to try and look overtop the stairs hallway where there is. Your idea of shrink tubing was an excellent suggestion, I didn't think of that. My own prob is I don't believe there is any slack. When I bent the wires to remove the old fixture the insulatoin cracked on the hot wire right up where the cable enters the box. I could not pull any slack. I'm gonna remove the box to see if I can knock off a staple closeby and borrow that way, but....as you correctly noted, a little bit of luck is needed.
I really appreciate such an informative response, makes a lot of sense, but I never thought of it and prob never would have were it not for this situation.
I had the same problem in my kitchen and bath (80 yr old house); do they have an old-fashioned, enclosed "barrel" type fixture? They get hot, and if someone uses a 100 watt bulb the wires are toast.
For the bath I was able to run a new wire in from the switch, but the kitchen I had to go back 2 feet to get to good wire (which is old metal clad, cloth-covered wires) and put in a junction box to connect new new to old. All in a plaster ceiling. Yuck. Probably easier to re-wire from scratch.
I hate to show my ignorance but...I'm not sure what you mean by a "barrel" fixture. This was a ceiling fixture, single socket with about a 6inch round base that attached to the box/ceiling and a typical glass globe.
like this: the globe looks somewhat like a barrel http://www.lowes.com/lkn?action=productDetail&productId=78222-1185-7710WH
Another option is to remove the old box and see where the wire goes, if you can go back downline a couple of feet you can put in a splice box and decorate it with a working 120v smoke detector or another light. From there just put in a new feed to the old light location.
bake
Good idea. I have also, when forced and laking time and options used one of the better designed textured round 'blank' plates. Once painted they disappear quite well.
This is slightly off the subject, please forgive me, but: couple days ago the guy I work with was doing lots of wiring and I sort of noticed an odor, but before the thought fully reached my brain, the guy wrinkles his nose and says he smells something. I said I did too. He says it smells like burning wire. Not a good thing when you're wiring! So I grab his battery work light so he can go back in the attic to look things over and the light is hotter than a five dollar pistol. Turns out it fried itself somehow. The bulb was still good, but the socket was burnt and melted. Although he had a ruined worklight, at least we didn't burn the house down! I hate explaining that to the owners!
The old wiring problem is often exacerbated by the HO using oversized bulbs in the fixtures (often 100-150W in a unit rated for 60W). But it occurs to some degree anytime a close-to-the ceiling fixture has been in place for several decades.
Re the new fixtures that require higher temp wiring, I suspect that this doesn't represent any sort of change in the design of the fixtures, but rather a change in rules by UL and others, recognizing the above problems.
It would be nice if someone would make a double-compartment rework box for this situation -- something double-deep with a removable metal partition between the upper and lower parts. Would allow the wiring to be spliced with reasonable safety.
I replaced some old, square "can" hights in a basement
I am guess from the 60's or 70's.
They where rated for 150 watts and had fiber (asbestos?) insulation on the wire. If I remember correclty they where labeled to connect to 105C wiring. but where instead connected to old cloth romex.
But I did not pay too much attention to the condition of the wire as I was ripping the whole mess out. But one pair of them stopped working before I got to that part of the job.
This is the type of problem that HO DIY'ers should only investigate early on a Saturday morning, and preferably on a 3 day weekend. ;-) Mine was an intermittently functioning bathroom ceiling fixture. As I lowered the fixture the fixture wires started to pull apart the wiring in the 4" octagonal box such that it just rained little BB sized pieces of baked insulation. It was all twisted together, some soldered connection that were wrapped with tape. All wires came in through holes with no clamps or protection from cutting/abrasion. The box was a mess with 4 pair of wires coming into it and no clue as to who was who. Only after they were pulled could I identify incoming power, wire to switch, wire to mirrorlight, and light to adjacent room (which further fed the remainder of the branch.* This unfortunately was late on a Sunday in December, hence my warning about starting early. The other problem is that the attic area above the fixture was occupied by a gas furnace. I did at least have access to the wires going in and out of the box so I could pull new 14-2, slip on protective grommets, and make proper connections. I also replaced the ceiling fixture with a larger 2-bulb 60W unit so as to avoid temptation of anyone using a single 100W in the future.
This is something which I believe should be considered when purchasing an older home. All enclosed ceiling fixtures should be suspect. Those which might be buried in insulation will have the problem exacerbated. Unfortunately you can't tell what they are really like w/o taking them apart, AND, taking them apart may be irreversible as was mine. At a minimum circuits containing those suspect fixtures should probably be put on arc-fault breakers.
*There is no substitute for a complete mapping of all branch circuits in a house.