A couple of days ago one of my extension cords overheated, and the insulation melted off the wires along most of its length, almost causing a fire. I’m puzzled by what happened, since the cord shouldn’t have been drawing much current. For safety in the future, I’d like to understand why this occurred.
It happened while I was out of the house. Fortunately my cleaning lady, who comes once every two weeks, happened to be there. She smelled smoke while she was in another room, and came out to find the rug smoldering under the cord. Luckily for her the circuit breaker seems to have kicked in before she started to do anything about it, or else I don’t like to think what could have happened. When I came home, after she had left, I found she had taken the melted cord from the socket, and left it on a newspaper. There were scorch marks on the rug. I found out what happened after calling her.
The puzzling thing is that the only items plugged into the 3-socket cord were the power cords for my phone and answering machine (6 W each), and a floor fan (55 W) which I don’t think was even on. These same units have been plugged into the same cord for more than a year with no problems.
The extension cord is about 15 ft. long, and is rated for 1625 W/125 V. The last time I looked at it I didn’t notice any obvious problems, such as knicks or kinks.
The electric supply in Panama City, where I live, is basically the same as the U.S., 110-120 V. However, the supply can be somewhat irregular, and in my neighborhood there can be occasional blackouts for an hour or two every few months.
Any ideas about what could have caused the cord to overheat enough to melt?
Good post, if only to point out why you never, never run an extension cord under a rug.
Likely, foot traffic caused the wires inside the cord to wear until you had insufficient copper to handle the current that was running through the wire. Result, heat, and if the cord is under something flamable, fire. The you got to go out and buy all new stuff.
From what you’ve said, it is doubtful that the cord was electrically overloaded.
The statement
(bolding mine) has me intrigued regarding cord damage. A parallel arc fault could conceivably produce what you’ve described, but without viewing the damage in total, further comment is speculative.
You were fortunate, Colibri. I’m glad you’re OK. Message to everybody-stop using extension cords as a substitute for proper building wiring.
Correct, the breaker would trip if the cord shorted. But if the wire simply wore thin, it would happily supply energy to the cord/house burner device until it grounded and started pulling more amps than the breaker was rated for.
Not necessarily. Assuming the numbers in the OP are correct, the cord was rated at 13 A. If it was plugged into, say, a 20-A circuit, and was drawing 19 A, for example, the cord could easily have overheated without tripping any breakers.
EvilGhandi, the OP clearly states that the cord was run on the carpet, not under it. Though you may be correct about the root cause. People tend to be careless about stepping on wires.
What part of the extension cord got hot? From your post it sounds like the entire length of wire got hot. If so, then either the cord shorted at the appliance end or one of the appliances has an internal short. If I were in your shoes, I’d get an ohmmeter and check the fan, then the adapters.
Got to work on my reading skills here, of course, it was friedo that suggested short, and I appologize, I misread the OP and assumed the wire was under a rug, sorry to jump to conclusions.
You assume the appliance cord is rated as low as the extension cord. Bad QED, you know as well as I do that extension cords are frequently far over-rated and that a 14 guage cord, especially a cheapo one, is usually around 16 guage.
Viewing the cord, are there or is there a site on the cord which exhibits localized blackening? This site should be accompanied by visible breaks in the insulation.
:curious:
Colibri, another question would be, is the cord melted along one conducter or both? The wire should have two channels, one will be smooth the other will have ridges on it. Is one half more heat damaged than the other?
Dammit I hate this place, I had to leave about twenty minutes ago but this thread kept me in front of this infernal computing thing. I’ll look in later to see what comes up.
Even cheapo extension cords are typically UL listed (at least here in the US). I won’t buy one if it isn’t. If anything, the cords are often under-rated. My 1000 W (8 A @ 125 V) hair dryer, on the other hand, uses 18 AWG wire, which IMO is cutting it close for such an application. I highly doubt extension cord manufacturers are going to use 16 AWG in products labelled as using 14 AWG, since that would open them up to massive lawsuits.
Not really. There some effects on power factor and maybe some reflected impedance effects, but at 60 Hz, these are completely negligible as far as power draw is concerned. I’ve had dozens of transformers energized by a single branch circuit on a test bench where I used to work making the damn things. If you got a transformer question, I’m the guy to ask.
