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.
I'm convinced it's the difference in the thermal coefficient of expansion between the brass rivet and the aluminum shell. I've replaced several Edison sockets over the years. Though the ones in the little 150W PAR cans I use in a small stage-lighting rig are ceramic rather than phenolic, the construction is similar. Over the years I've had a couple of the replacements (from a U.S. manufacturer) fail as well, always with the same problem. But I'm old enough to remember Edison sockets with identical construction except that the shell was also a brass, bronze or copper alloy, not aluminum. I don't recall seeing this particular failure mode back then.
Not sure how drugs are examined to identify counterfeit, but the Independent Distributors of Electronics Association offers certification in identifying counterfeit electronic components. Apparently there are signs to help inspectors identify counterfeit components even though the counterfeiters are getting very clever (such as having legitimate components sitting on top of counterfeit components).
There's probably ONLY two manufacturers of these devices left in the U.S. / Canada, and that's LEVITON & EAGLE. You know that even IF they manufacture some items in China, they have rigid quslity control procedures in place to prevent such anomalies.
Jon touched on the very essence of the problem with this socket. An aluminum shell with brass rivets. That's the same lethal combination that was present in the late 1960s when copper was scarce due to the Viet Nam conflict, and houses were being built using aluminum wiring. Even the revised copper-clad aluminum wiring still posed a potential threat. IF you did any electrical work during that period, you learned very quickly to bathe the terminals in "NO-ALOX", or another anti-oxidizing compound to inhibit the formation of Al Oxide. And, terminals on devices were relabeled w/ the CU/AL logo to identify them as safe for either copper wire, copper-clad wire, OR aluminum wire.
Jon, thanks for this article and even more for your comment about counterfeit UL labels. How scary is that?! I knew about fake chips and drugs, but fake electrical compliance labels is something we can't "watch out for" as consumers--how the heck are we supposed to know they are fake?
Good point, TJ. We have counterfeit semiconductors imported from Asia, so it's no big deal to put a UL or CSA label on a component such as a light socket, particularly if purchasing and manufacturing occur somewhere in Asia. And it's not just counterfeiting of electrical and electronic materials. The FDA has many cases of fake drugs--Avastin, for example--coming from overseas "suppliers." In the case of Avastin, the source of the fake drug didn't even bother tp try to reproduce the type of label Genentech puts on the real drug and it still got through several distributors.
Naperlou, the independent party testing label is still not a guarantee of a good design, or even of a valid part. UL is constantly watching out for parts with counterfeited labels. The parts most commonly seen with such false labels come from overseas because it is difficult to prosecute.
Jon is correct. You really need to look for the UL, or similar, testing labels. Cheap parts are nice in that they keep the price of products down. On the other hand, as Mydesign points out it can be dangerous if you are dealing with electricity.
As for an new design for lightbulbs, the reason this has not been changed is that the manufacturers don't want to force the cost of an upgrade on the consumer. This is nice, but it also perpetuates poor design choices of the past.
Jon, quality and finishing matters a lot, especially anything related to electricity. It's not safe to handle any devices made of poor quality materials, which can end up in electric shock. Proper design to handle the device is also important.
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