Hello there,

There are a lot of sites on the web that tell you to test an extension cord with an ohm meter. But that is hardly a test at all, being only for basic functionality. It doesnt tell us how well the extension cord handles current. The cord needs to be tested with current, for extended periods of time. If it gets too hot there is a problem.

The main reason i am writing this though is because i have tested a number of them now, and find that the receptacle end gets very warm, while the plug end stays very cool. Even a more expensive cord did this with load current from about 5 to 8 amps. All cords rated for 15 amps.

I really want to find out what is going on here.

So the question is, anyone have any idea why this happens, and did you ever notice this too?

 

hi Al,
I have seen a number of my mains extension sockets that have heat 'browning' of the outer plastic around the socket areas.
The extension socket current loading is well below 13Amps [UK fusing]
The internal wiring appears OK, screws secure etc ...

I suspect the problem is caused by low quality metalwork of the actual contacts that are supposed to 'grip' the inserted plug legs.
Insufficient contact pressure between the plug legs and the mating metal socket would be a cause of heating.

E

 

Most extension cords are just crap with weak spring contacts and poorly crimped connections. For long term use we build our own with an electrical box and high quality parts.
http://www.hubbell-bryant.com/literature/BPB103HealthcareBrochure.pdf

 

hi Al,
I have seen a number of my mains extension sockets that have heat 'browning' of the outer plastic around the socket areas.
The extension socket current loading is well below 13Amps [UK fusing]
The internal wiring appears OK, screws secure etc ...

I suspect the problem is caused by low quality metalwork of the actual contacts that are supposed to 'grip' the inserted plug legs.
Insufficient contact pressure between the plug legs and the mating metal socket would be a cause of heating.

E

Yupper! Resistive heating is the getter! --- @MrAl Inasmuch as you have experienced trouble with multiple cords, is it possible the the plug{s} of the connected device{s} are culpable?

Best regards
HP

 

hi Al,
I have seen a number of my mains extension sockets that have heat 'browning' of the outer plastic around the socket areas.
The extension socket current loading is well below 13Amps [UK fusing]
The internal wiring appears OK, screws secure etc ...

I suspect the problem is caused by low quality metalwork of the actual contacts that are supposed to 'grip' the inserted plug legs.
Insufficient contact pressure between the plug legs and the mating metal socket would be a cause of heating.

E

Hi there Eric,

Long time no talkie

I will check this out today sometime. I am pretty sure it makes good contact though, because the prongs of the plug go in pretty tight. But i will check this out better and see if this has any effect.

 

Most extension cords are just crap with weak spring contacts and poorly crimped connections. For long term use we build our own with an electrical box and high quality parts.
http://www.hubbell-bryant.com/literature/BPB103HealthcareBrochure.pdf

Hi,

Yeah i think i have to agree with that. It's funny how crappy they can be.

 

Yupper! Resistive heating is the getter! --- @MrAl Inasmuch as you have experienced trouble with multiple cords, is it possible the the plug{s} of the connected device{s} are culpable?

Best regards
HP

Hi,

That's actually a very good question, and one that i considered and found that the plug can contribute some heating effect in the socket too. I switched to an almost new plug with shiny contacts. I also clean old ones now and then too to keep them shiny. Same with three prong adapters.

I think that this has an effect when plugged into the wall too, where the plug is dirty and thus does not make good enough contact.

The best test seems to be a long hours test run and then use an IR temperature gun to measure temperature.

 

The best test seems to be a long hours test run and then use an IR temperature gun to measure temperature

hi Al,
Modify an old PC web cam, remove the IR filter and view the offending part in the IR region of the spectrum.

E

 

hi Al,
Modify an old PC web cam, remove the IR filter and view the offending part in the IR region of the spectrum.

E

Are CCDs sensitive to far infra-red? --- *very* nice to know if true

 

I've noticed this resistive heating problem in both ends of the cord in overmolded assemblies and have always thought it was caused by a thinned cross-sectional area in the crimps. No doubt we've all seen cases of loose or dirty receptacles causing the problem also but now I'm wondering if the contact alloy is a factor since it's not as conductive as the wire it's attached to. UL probably has statistics on this but I'm not going to research it.

 

Are CCDs sensitive to far infra-red? --- *very* nice to know if true

Many examples on the web.

http://www.wikihow.com/Make-a-Webcam-Into-an-Infrared-Camera

 

Many examples on the web.

http://www.wikihow.com/Make-a-Webcam-Into-an-Infrared-Camera

Thanks for the reply

Note, however, that the linked page states that functionality is extended only to near infrared --- Hence response to far infrared radiation (e.g. 'radiant heat', etc...) seems dubious --- All the same, you've got me interested in the 'response curve' for 'standard' consumer grade CCD imaging devices...

Best regards
HP

 

Hi,

Interesting idea Eric. They also sell IR sensitive web cams pretty cheap. Maybe if it was held close to the plug it would pick something up.
My IR temperature gun has a fine sense diameter at close range, so i can move it up and down the length of the socket (which has three outlets in a row, not all on the same side). I plugged the test wire plug into the center socket because that was the tightest, and i am finding that the hottest point seems to be at the end of the socket set where the wire enters the socket chamber. This leads me to think that the wire is not connected to the metal that makes up the socket very well.
What i might do next is cut the socket chamber plastic away so i can see inside. This will probably help me to spot the bad connection, if that's what it really is. I figure if i do this carefully i can solder the two wires, then retest. If it remains cool then we know what it was for sure.

Oh yeah there is one more possibility i almost forgot about, although i cant see this happening with a brand new extension cord...
The area where the wire enters the socket chamber (molded or not) has no standard cord relief. That means when the cord flexes left and right the wires inside could start to break, one strand at a time, until there are only a few strands left inside the wire. I have seen this happen with appliances that do not have an adequate cord strain relief where the cord meets the appliance body. Eventually one wire breaks completely and that means the appliance doesnt work at all anymore.
I doubt that is what happened here, because this cord was new although kept hanging on a nail for a couple years now, but never used, so the cord would not have been flexed very much if at all. But i thought i would mention this too.

So my guess now is that we are looking at a bad crimp. I just have to figure out the best way to cut this end apart so i can get it back together temporarily for the next test. I dont want to mess up the contacts because then i couldnt test it later, although a bad crimp can probably be spotted by eye as some of the strands will appear to be loose i bet.

Just started testing another cord about a half hour ago. The end with the sockets gets warm too, but this time it feels like the wire within about 6 inches from the socket is what is getting warm. I noticed that with the other one too but attributed it to the socket, not the wire. I'll have to test it a little longer to see if the socket heats up too, but that might mean that the wire heats up the socket not the other way around. This is strange...

Also, found this:
http://www.thermalvision.ie/2013/04/can-i-make-a-thermal-imaging-camera-with-a-webcam/

 

"Far Infrared" is in the freezing region and is used by "radiant heat" sales people as a slogan. Most things on earth are in the 5-20 micrometer range, clearly in the mid band of IR emission. Cameras with Ge:Cd or Ge:Cu sensors are good candidates for this application.

I deal with a lot of 120V equipment drawing 12-15 amps. The problems I fond with overheated cable ends is mostly workmanship. Poorly stripped wire ends (nicked solid wire or strands cut off) and poor and wrong crimping techniques are the main culprits. And don't get me started on the AC outlets in N. A., There are screws there for the wire, but also those little holes to stick the 14 gauge wire in, a cause of much grief! A 14 gauge cable will get quite warm to the touch if you put 15A through it. E

 

Hi,

At 12 to 15 amps i guess you find the bad ones pretty quick

I found one cord now that doesnt get warm, only a little near the joint between the wire and the socket body. Barely warm though. This isnt an expensive cord while the other one i was testing was more expensive but got much warmer, so i am sure that one needs repair, even though it is nearly new (hanging up for a couple years but more or less unused). The more expensive and hotter one was made in the Philippines and branded "Huskey" and sold by Home Depot.

 

...Most things on earth are in the 5-20 micrometer range, clearly in the mid band of IR emission. Cameras with Ge:Cd or Ge:Cu sensors are good candidates for this application

Very interesting!!! I was thinking ca. 120 milli-eV (i.e. λ~10 um) in what products would you expect to encounter CCDs responsive to such wavelengths?

Very best regards!
HP

 

"warm" doesn't mean anything really.. and doesn't necessarily indicate a problem either..
A problem would be as you get close to the 75 deg C range (thats HOT) or in excess of the rating of the wire insulation.
Thats really all the safety agencies care about/test for..

You can't compare price either as an indication of quality nor current carrying capability..

Wire gauge is what you should be looking at..
Expect comparable gauges to be similar in temps..

Not sure how you are determining that the plug end remains cooler than the receptacle end nor how your test is setup and connections are made but one might assume that being exposed directly to the air and not being "shielded" by a poor thermal conductor like plastic/rubber would effect that too along with differing surfaces area..

 

"warm" doesn't mean anything really.. and doesn't necessarily indicate a problem either...

unless efficiency is an issue... of course

 

The physics of the particles bouncing around and moving is what causes the heat isn't it?

That being said, are those particles likely to dam up at the exit end (socket), and bounce around in a tighter space, causing extra heat?

If not at the prong end, but only at the socket end, then maybe physics is playing a role?

If they all do it, then what is the worry?
Just don't run the cord under the carpet.

Heck, I don't know!

Interesting thread.
Thanks

 

The physics of the particles bouncing around and moving is what causes the heat isn't it?

That being said, are those particles likely to dam up at the exit end (socket), and bounce around in a tighter space, causing extra heat?

If not at the prong end, but only at the socket end, then maybe physics is playing a role?

If they all do it, then what is the worry?
Just don't run the cord under the carpet.

Heck, I don't know!

Interesting thread.
Thanks

Actually it's not that complicated. The contact heats up because there is resistance at the points of contact. As all materials have resistance, what's happening here is that the points of contact are fewer than is actually needed, and most current will go through them, instead of going through a larger contact area that will diminish the resistance... it's like having a hose that's being pinched at one point of it's length... water will be strained through that section, and although it will still flow, the flow (current) at the end of the hose will be smaller than it should. And the hose will heat up at the point where it's being pinched... Regarding this water hose analogy, the hose will really heat up, though of course with a negligible temperature increase.