A three-way socket on my bedside lamp gave out recently, but not without first overheating and causing a burned-phenolic-like odor.
When I disassembled the lamp socket, I noticed black material around the point of contact between the aluminum socket shell and a hollow brass tube that was press fit, or swaged, into place. This fitting connects the shell to power-line neutral. Perhaps a loose fit or differences in thermal expansion of materials caused a slow increase in resistance between the brass and aluminum. That resistance led to a hot spot. (This socket, shown below, did not have UL or CSA logos.)
This type of three-way socket has a third contact, which remains rigid and touches a conductive ring on the bottom of a bulb. It makes contact by digging into a contact ring on three-way bulbs, but it lacks resilience. After a while, the resistance between this off-center contact and the ring on a lamp base increases. That resistance can lead to arcing, overheating, and a bad odor, if not a smoldering socket. I have replaced many sockets because of this design shortcoming.
It's a shame that the move to LED lights hasn't sparked ideas for new types of lamp sockets and a new lamp-base style that overcomes design problems. Automotive lamps provide good examples of simple sockets that make bulbs easy to install and extract and ensure good connections. Manufacturers mold the wire contacts into the glass base, and the socket comprises simple contacts. Some automotive lamps use a molded plastic base instead. Contact-on-contact wiping action and resilient metals help ensure low-resistance paths.
Perhaps someone could design a practical and safe push-in/pull-out socket for LED bulbs. This type of socket would simplify changing bulbs, too. Vaulted ceilings require an extension pole with either a wire basket for globular bulbs or a suction cup for flood lamps. If you use a helical CFL bulb in high places, you might have to fashion your own tool to insert and extract them. And if the glass bulb separates from the socket, you must haul out a ladder.
Mismatched materials, cheap manufacturing techniques, and inattention to quality could lead to disasters. For lamp sockets, at least, it's time for a new approach to design, materials, and manufacturing quality. Also, look for UL and CSA markings before you buy electrical products.
Hi, OLD_CURMUDGEON. The electrical code specifies a certain size box given the number and gauges of wires in the box. So if you overstuff a box, your work won't pass inspection. Boxes should have their volume clearly marked and a calculation yields the volume needed for the wires. Fine Homebuilding magazine ran an article that includes an example: http://www.finehomebuilding.com/how-to/articles/more-wires-need-bigger-boxes.aspx.
Jon, I think you're dead on about the need for an update in socket design. I'm also pretty sure it won't happen any time soon just because of the enormous number of installed sockets. If a good design comes forward that could be easily fitted to existing sockets by using a screw in adapter it would have a much better chance.
Your particular problem is primarily because of the 3-way design. In the standard base, the rivets don't have to remain tight because the spring on the center contact keeps them held against the socket shell. Because the third contact of your socket is solid, the only thing holding the rivet tight is the springiness of the socket shell and that doesn't have enough "give" to be much help. If you can't find a socket with a spring third contact the addition of a screw might be your best shot, especially if you add a spring lock washer.
While a brass socket shell SOUNDS like a good idea, it has one major flaw: all modern light bulbs have an aluminum base. Brass sockets went out of favor soon after bulb bases changed to aluminum, probably because electrolytic corrosion started cementing bulbs into sockets.
Best of luck in your quest for the perfect socket :-)
Even aluminum-on-aluminum sockets can have problems, so i always put a thin coat of high-temperature silicone vacuum grease on threads before I screw in a new bulb. I use Dow-Corning "High Vacuum Grease." The price ranges from about $20 to $32 for a 150-gram tube, but it will last for several generations. I also use this grease on outdoor electrical and RF connectors to provide additional water resistance.
Toward the end of the 1960's, aluminum was used for house wiring. There were fires, initially in travel homes, but later, regular homes also experienced fires. The cause was aluminum wires. Aluminum has two properties that caused this problem. First, it is a soft metal, and second, its oxide is a tough film, and an insulator. In the case of the home wiring, vibration in mobile homes during delivery or driving, loosened the screws in the receptacle and socket contacts. This was followed by oxidation and a reduction in the contact area because some of it was oxidized and became an insulator. The result was heating at the contacts.
A similar problem arose with stationary homes. Here, since the aluminum wires were softer than the brass contacts, if the wires at the contacts heated enough, the aluminum would deform because of the restriction of the contact screws. When the contact cooled, the aluminum would contract and now there would be space where the aluminum could oxidize.
It is possible that this mechanism was the cause of the failed socket.
I read so many posts in this publication about the failures of new elecric devices that I have to wonder if any manufacturer knows how to make reliable electrics today. I am a fan of estate sales and have a great deal of luck with refurbishing old stuff.
On the aluminum wiring, I heard years ago that it has a higher resistance than copper, so powering the exact same devices in a house with aluminum wire will cost more than if the wire is copper. Does anyone know if that is correct?
I also replace all "bulb down sockets" with pocelain. Ceiling fans for example and put a drop of WD 40 on aluminum light bulb bases. It seems to make bulbs easier to change.
Yes, aluminum has a higher resistivity than copper, but the resistance overall is so low compared to the load resistance that you lose an insignificant amount of energy in either type of wire. Instead of WD-40, try the silicone grease I recommended in an earlier blog post. WD-40 is a water displacement agent used to help prevent corrosion.
Jon Titus wrote: " I also thought about running a 2-56 bolt through the brass tubing, tightening it and locking it in place. I might do that if I can't find an Eagle or Leviton replacement with a solid connection. We'll see..."
Jon, I've done this. I had to drill through the rivet, thinning it's walls, for the 2-56 machine screw to clear. The repair was easy and successful.
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