I don’t suppose the extension cord could have been coiled neatly? The induction effect might cause the overheating damage you mention, but it would have to be coiled for the whole length of the damaged bit for this to be a viable theory.
Coiling won’t make one bit of difference from an induction-heating standpoint. First of all, an inductor doesn’t generate heat. (An ideal one, at least.) Secondly, the magnetic flux produced by the hot & neutral conductors would mostly cancel, thereby greatly decreasing the impedance. (This is because the hot & neutral conductors are very close to each other, have the same current magnitude, and have opposite directions in current.) Thirdly, if there’s some induction in the cable and there’s a short at the end of the cable, the extra impedance would only serve to decrease the overall current.
Now having said that, it is true that coiling an extension cord can cause a fire. But this is only due to I[sup]2[/sup]R heat buildup in the deeper parts of the coil.
I have a completely different take on this one.
I suspect that your cleaning lady may have pulled the extension cord out of the socket and stuck it in your oven, baking it until it had melted. She then plugged it back into the wall with the intention of creating a small fire that she would ‘heroically’ extinguish.
Her reason for doing this would likely have been to create a lot of ‘drama’ in her life and to draw a great deal of ‘attention’ toward herself, which she desparately desires.
Next week she’ll probably have a miscarriage while she’s vacuuming your rug, the week after that someone will rape her while she’s scrubbing your toilet, the week after that someone will cut her brake lines…
I receivd the cords today, and a preliminary examination is rather disturbing. A vernier caliper measurement of the exposed wire reads .033", which is roughly 20 AWG solid, or 21 AWG stranded–WAY too thin for its ratings (1625 W @ 125 VAC). Additionally, the three-outlet female end is not a molded assembly, but rather is a snap-together unit with brass stampings for contancts, to which the wires were soldered. There was no crimping or any other form of strain relief present. One of the solder beads is intact (on the neutral side), and appears as if the wire was broken off right at the joint. The other (hot side) appears to have been melted off, most likely due to the overcurrent heating. This is most likely the source of failure: one wire broke loose and made momentary contact with the other inside this connector, causing the overloading and subsequent cord damage. If only one or two strands of the wire made contact, it is conceivable that there was an insufficient load to trip the circuit breaker while drawing enough current for a sufficient length of time to do the damage seen, especially given the undersized wire used. I have not yet determined why the neutral side of the cord seems to have suffered more damage than the hot side–both sides used the same wire gauge.
These cords are poorly made and extremely dangerous.
I took some low-res shots with my webcam.
- The outlet end opened for an inside view.
- The damage to the cord itself.
- The solder attachment of the wires to the inside of the female end. (The “strain relief” was cut off to show the connection).
Thanks very much! It’s very helpful to know that the source of the problem seems to be the cord, rather than the other appliances.
I guess they must have been ones I obtained here in Panama. (It’s possible that they were here in the apartment when I moved in.) I’m not sure where they might have been manufactured - the tags are in English. I’ll check all the others I have in the house and make sure they from the U.S. and are rated by the UL. (One can purchase U.S. manufactured cords here with UL certification.) I’ll toss any for which I have any doubt.
I had cable/DSL installed in my apartment earlier in the week the incident took place. It’s possible that one of the workmen might have stepped on the cord or plug or otherwise somehow initiated the damage.
Once again, thanks.
Just to add a thought that nobody else has brought up - why are we assuming that the melted wire was the neutral? In the US, it’s pretty hard to find a non-“safety” outlet with one whole larger than the other, but I would not assume the same in Panama.
QED, were the male prongs of different sizes? (The cord doesn’t seem to have ground, so there shouldn’t be a grounding pin).
Colibri, do your outlets have different sized holes, forcing you to plug a cord in only one way?
Our house in Jamaica had funky old outlets, and you could plug a safty plug in either direction - my dad and I had to replace all the outlets. Some of them were wired incorrectly as well (missing ground, usually). :dubious:
Not to rain on the parade, but here is a CPSC report involving counterfeit UL labels.
This is a CPSC link regarding undersized cords and UL/CSA markings without listing numbers.
I’ve been away from the business for a while, but I do remember harmonics causing overloading in the neutral of certain (non-linear ?) loads. But that was mostly with laser printers and other such equipment. (Blank)-switching loads, IIRC.
Sorry, me own lovely synapses seem to be zero cross-firing. 
Peace,
mangeorge
Just as a thought, if you haven’t tossed any cords yet, should you think about severing them so they can’t be used by someone else?
Yes, they are polarized outlets (or else they appear to be - you can’t be sure of very much in Panama).
[quote=Just as a thought, if you haven’t tossed any cords yet, should you think about severing them so they can’t be used by someone else?[/quote]
Yes, I thought of that and will do so. I wouldn’t want my cleaning lady recycling them! (But I think she had enough of a scare not to do so.)
danceswithcats, thanks for the links. It looks like this is not just a third-world problem. I’ll just have to be as careful as possible about the cords I use.
I missed this thread until today but the cause seemed clear to me while reading the OP.
If the wires shorted directly to each other, as in the case of a stepped-on break, the breaker would have tripped at once.
For the slow burning action as decribed and having now seen the pictures, the cord must have been overloaded. I immediately thought of a vacuum cleaner. These often advertise high amperage draws as a selling feature.
There are, in general, two classes of high powered household devices: motors, as in power tools air conditioning, and vacuums, and heat-generators, as in lighting, space heaters, tanning lamps, hair dryers, and coffee pots. There’s others (RF like microwaves and transmitters, for example) but these aren’t as common or seem silly (toaster oven in the bathroom, etc).
Not to accuse the cleaning lady of anything criminal or whatever but my money is on that she used the cord for something it wasn’t made to handle.
As I said, I’m pretty sure she didn’t. The vacuum cleaner was not operational, and I can’t think of anything else she might have tried to plug into that socket. If she were using the iron, she would have used it in the laundry room.
For the record, my cleaning lady is extremely reliable. She has worked for me for 12 years, and has her own key to my apartment so she can come in while I’m at work. (She also works for several of my friends.) She has always told me right away when she has accidentally broken something, over-bleached a shirt, or had any other problem. If I leave money in the pockets of my clothes in the laundry, I always find it set aside on the kitchen counter. The next time I see her I will ask her again, but I would be very surprised if she were misrepresenting the circumstances of what happened.
Not necessarily. In the case of a very small contact area (in other words, relatively high resistance), thee can be considerable current flow without necessarily tripping a breaker immediately. Given the extent and nature of the damage, it appears it happened relatively quickly, say on the order of a few minutes. There also is NO damage whatsoever to either the male two-prong polarized plug, or the three-outlet female end, indicating the absence of a severe overload. No, it was almost certainly an internal fault caused by the shoddy construction and substandard materials used.
Sign up our VIP Q.E.D for CSI PDQ.
I second. So moved?
QED, is your only sticking point the fact that the “return” was more melted than the “live”? I suspected that the outlet was not polarized, but Colibri swears it’s not so (thanks, btw, I could not remember the term! sheesh). So I’m gonna fall back on the not unlikely possibility that the outlet was just miswired, swapping live for return.
Colibri, you should cease henceforth from buying extension cords that are designed to kill you, and resort to killing yourself in normal ways, like drinking excessively and indulging in dangerous sports. And get a cheapo tester and check your outlets. We’d miss you otherwise.
All I can say is that all the wall outlets in the apartment have 3-prong polarized sockets. I have not yet investigated the outlet concerned, as it is behind a bookcase (the reason I was using an extension cord in the first place). How would I recognize a mis-wired outlet? Would that have an effect on any appliances plugged into it? As I said, the appliances work fine. This is the first problem of this nature that I have had in this apartment.
Thanks. The way I expect to go is in a helicopter crash on a remote jungle mountaintop, or in the course of being kidnapped by Colombian guerillas. Or maybe a Bushmaster bite. Or Ebola fever. (All occupational hazards in my line of work.) An extension-cord electrocution is a bit too pedestrian.
I usually consider myself to be a guy who likes history, comedy and sharp witty rejoinders. I like human drama and BBQ-pit smackdowns.
However…
This has been just about the best thread I’ve read all year. I can’t explain how fascinated I was. It was like a murder mystery. I only wish I could follow all the electrical engineer terms with having to google back and forth to understand them.
I want more info on that “Killer Kord” ! I’ve got to point this out to my electric wholesale friend, he’d get a kick out of this.
Thanks, guys.
Oh great. Not only is he dimmer than a 10-watt bulb, and got us into what even Cecil calls a “damn fool war”, now you’re telling me he’s venomous?!
Well, no, it’s a Bushmaster, and that would be Cheney. 
In any case, you definitely don’t want to tread on one.
The scientific name is especially apt: Lachesis muta, after the one of the three Fates in Greek mythology who measured out the length of one’s life, and muta, meaning silent. In other words, “silent death.”