# Why did my extension cord melt? **URL:** \ **Category:** Factual Questions\ **Created:** [May 22, 2004, 9:03pm UTC](https://boards.straightdope.com/t/why-did-my-extension-cord-melt/246572 "2004-05-22T21:03:14Z")\ **Posts on this page:** 12\ **Page:** 5
**Author:** ![Drum\_God](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drum_god/32/44_2.png) [@Drum\_God](https://boards.straightdope.com/u/Drum_God)\ **Post date:** [June 2, 2004, 10:03pm UTC](https://boards.straightdope.com/t/why-did-my-extension-cord-melt/246572/81 "2004-06-02T22:03:32Z")
> [@David Simmons](#): > > Once again illustrating the deficiency in the electrical code and the UL listing process. It is entirely possible to start an electrical fire and never trip the breaker. Many flourescent light fixtures, and table lamps have wiring that is only adequate for the expected load in the fixture which might be a couple of amps. So they allow a big safely factor and put in wire rated at 5 amp. You plug this into a 15 amp receptacle, a short or partial short develops in the light fixture which draws 10 or 12 amps and Bingo! you’ve got a fire. Happens all the time. > > We need to start a movement to demand that each appliance plug contain a fuse rated for the current the appliance draws. I think this happened to me. Last week, I turned off a 3-way lamp in the living room and went to bed. In the morning, no one went into the living room and the lamp was never turned on. At lunch, my wife discovered that the plastic knob had melted on the socket. She turned the switch anyway, heard a “sizzle”, and unplugged the lamp. When I came home and discovered the problem, I disassembled the socket. There were severe burn marks on the bulb base and inside the socket. When I removed the socket interior, the scorches continued onto the power cord. The heat must have been intense, because it melted the plastic knob on the switch. In fact, the heat likely saved the house – it seems that it burned through the switch, which disconnected the power. Maybe the switch was intended to be a fuse. I replaced the socket interior, replaced the bulb, and have had no further problems. I can’t imagine what would have caused the lamp to burn like that. The light bulb was well within the limits on the lamp’s label. Nothing unusual was done with the lamp. It was plugged directly into the wall - no extension cord. I have another matching lamp that now I’m worried is going to spark. ---
**Author:** ![BMalion](https://avatars.discourse-cdn.com/v4/letter/b/e274bd/32.png) [@BMalion](https://boards.straightdope.com/u/BMalion)\ **Post date:** [June 3, 2004, 11:39am UTC](https://boards.straightdope.com/t/why-did-my-extension-cord-melt/246572/82 "2004-06-03T11:39:30Z")
> [@Drum God](#): > > … Maybe the switch was intended to be a fuse… Is this possible? Is this ever done? ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [June 3, 2004, 5:20pm UTC](https://boards.straightdope.com/t/why-did-my-extension-cord-melt/246572/83 "2004-06-03T17:20:22Z")
> [@Colibri](#): > > 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. You can buy a gizmo called a **three prong tester** for about $8. One end has a two blade and round pin plug that will fit into a wall socket. The other has three LEDs, two green and one red. You plug it in and see which LEDs light. Okay is two green. Only one green or a green and a red means there’s something wrong. A bitty chart on the body will tell you what (Crossed hot and neutral, missing ground, etc.) Any time I move I check the sockets in the new place to make sure they’re up to snuff. It’s well worth the peace of mind. DD ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [June 3, 2004, 5:27pm UTC](https://boards.straightdope.com/t/why-did-my-extension-cord-melt/246572/84 "2004-06-03T17:27:07Z")
> [@BMalion](#): > > Is this possible? Is this ever done? Not insofar as I’m aware. Switches are designed to…wait for it…switch. Certainly, they may burn out if their current-carrying capacity is exceeded, but to rely on this happening or to engineer a switch to double as a fuse strikes me as somewhat silly. I think in this case, it was merely a fortuitous occurrence. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [June 3, 2004, 6:29pm UTC](https://boards.straightdope.com/t/why-did-my-extension-cord-melt/246572/85 "2004-06-03T18:29:38Z")
> [@mangeorge](#): > > 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. Why would harmonics cause more current to show up on the neutral vs. the hot? If there’s no ground fault, then the current on the hot must _exactly_ equal the current on neutral, regardless of anything else. (However, the current _density_ could be different if the gage of the wires are different.) ---
**Author:** ![danceswithcats](https://avatars.discourse-cdn.com/v4/letter/d/9e8a1a/32.png) [@danceswithcats](https://boards.straightdope.com/u/danceswithcats)\ **Post date:** [June 4, 2004, 10:46pm UTC](https://boards.straightdope.com/t/why-did-my-extension-cord-melt/246572/86 "2004-06-04T22:46:10Z")
[Here is an article](http://www.ecmweb.com/mag/electric_fundamentals_harmonics/) on the subject of waveforms, [and another.](http://www.pge.com/docs/pdfs/biz/power_quality/power_quality_notes/harmonics.pdf) Google for “triplen harmonics” and you’ll have a bit to read. This is the reason why I suggested use of an oscilloscope for modern diagnostics-a VOM cannot read waveforms. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [June 5, 2004, 2:31am UTC](https://boards.straightdope.com/t/why-did-my-extension-cord-melt/246572/87 "2004-06-05T02:31:43Z")
> [@danceswithcats](#): > > [Here is an article](http://www.ecmweb.com/mag/electric_fundamentals_harmonics/) on the subject of waveforms, [and another.](http://www.pge.com/docs/pdfs/biz/power_quality/power_quality_notes/harmonics.pdf) > > Google for “triplen harmonics” and you’ll have a bit to read. It is true the neutral can be overloaded in a _polyphase system_. But we’re not talking about a polyphase system here; we’re talking about an isolated load with a single hot and single neutral going to it. In this case, the instantaneous magnitude of the current in the hot wire must _ **exactly** _ equal the instantaneous magnitude of the current in the neutral wire (assuming no leakage current to ground) regardless of harmonics. But while it is true the current in the neutral wire must equal the current in the hot wire, the _resistance_ in the neutral wire may be different than the resistance in the hot wire. Furthermore, the amount of insulation around the neutral wire may be different than the amount of insulation around the hot wire. This means the hot and neutral wires may be at different temperatures, even though they both have identical currents. ---
**Author:** ![Klaatu](https://avatars.discourse-cdn.com/v4/letter/k/e0b2c6/32.png) [@Klaatu](https://boards.straightdope.com/u/Klaatu)\ **Post date:** [June 5, 2004, 3:21am UTC](https://boards.straightdope.com/t/why-did-my-extension-cord-melt/246572/88 "2004-06-05T03:21:11Z")
Well, as was mentioned, the cord was plugged in behind a bookcase, so maybe said bookcase was pushed up against the cord, effectively jamming the cord against the termination/plug thus over time causing wire wear/breakage creating a short. Occam’s Razor and all that… ---
**Author:** ![danceswithcats](https://avatars.discourse-cdn.com/v4/letter/d/9e8a1a/32.png) [@danceswithcats](https://boards.straightdope.com/u/danceswithcats)\ **Post date:** [June 5, 2004, 3:57am UTC](https://boards.straightdope.com/t/why-did-my-extension-cord-melt/246572/89 "2004-06-05T03:57:44Z")
From my second link: Single-phase non-linear loads, like personal computers, electronic ballasts and other electronic equipment, generate odd harmonics (i.e. 3rd, 5th, 7th, 9th, etc.). The troublesome harmonics for single-phase loads are the 3rd and odd multiples of the 3rd (9th, 15th, etc.). These harmonics are called “triplens” and because the A-phase triplen harmonics, B-phase triplen harmonics and C-phase triplen harmonics are all in the phase with each other. They will add rather than cancel on the neutral conductor of a 3-phase 4-wire system. This can overload the neutral if it is not sized to handle this type of load. While I don’t believe triplens to be causal in this situation, given the data posted by **Q.E.D.** , they are worthy of investigation, which was the point I sought to make when originally speaking of them. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [June 5, 2004, 5:14am UTC](https://boards.straightdope.com/t/why-did-my-extension-cord-melt/246572/90 "2004-06-05T05:14:49Z")
> [@Klaatu](#): > > Well, as was mentioned, the cord was plugged in behind a bookcase, so maybe said bookcase was pushed up against the cord, effectively jamming the cord against the termination/plug thus over time causing wire wear/breakage creating a short. No, that wasn’t the case. The cord wasn’t jammed against anything. In any case, **Q.E.D.'s** results indicate the problem was inside the 3-socket female plug, which was not behind the bookcase. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [June 5, 2004, 11:10am UTC](https://boards.straightdope.com/t/why-did-my-extension-cord-melt/246572/91 "2004-06-05T11:10:52Z")
**Danceswithcats** : For single-phase loads, they’re not talking about the neutral _ **at** _ the load. They’re talking about _ **another** _ neutral that this neutral connects to. This “other” neutral is sometimes a polyphase or shared neutral. So for the third time, I repeat with utter confidence: for an isolated load connected by a single hot wire and single neutral wire (such as the case with this extension cord), the current on the extension cord’s hot wire must be _ **exactly** _ the same as the current on the extension cord’s neutral wire. At _all_ times. _Regardless_ of harmonics. Or anything else. Look up **Kirchoff’s Current Law** if you have time. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [June 5, 2004, 4:03pm UTC](https://boards.straightdope.com/t/why-did-my-extension-cord-melt/246572/92 "2004-06-05T16:03:24Z")
> [@Crafter\_Man](#): > > …for an isolated load connected by a single hot wire and single neutral wire (such as the case with this extension cord), the current on the extension cord’s hot wire must be _ **exactly** _ the same as the current on the extension cord’s neutral wire. At _all_ times. _Regardless_ of harmonics. Or anything else. Indeed. If this were not the case, then GFCIs would be utterly worthless. [Previous page](https://boards.straightdope.com/t/why-did-my-extension-cord-melt/246572.md?page=4)