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#3600029 - 01/14/15 01:02 PM Some Extension Cord Testing
jstutz Offline


Registered: 10/06/08
Posts: 1556
Loc: NC
Last week i did some testing on my extension cords and thought i would share my findings. It is known that most cords fail under high load and at the ends. So here is how i decided to do the initial testing. I have a radiator heater that draws 1500 Watts on high which at my household voltage of 123V is 12.2A continuous. Run the heater on high for 5 mins through each cord and observe where the heat is generated and how much of it. I didnt go as far as to measure the temp with a thermometer but just touch and note if it is cool, warm , hot ect.

I tested 15 cords total
1) Bulldog Tough, 14 awg 25ft, OEM ends
1) MilSpec, 12 awg, 20ft OEM ends
1) US Wire Extreme, 50 ft , OEM ends
1) Voltec 16 awg, 25 feet extreme cold weather cord
3) Homemade with 16 awg and 14 awg computer cords with the end cut off and a duplex metal box attached to the end
1) Harbor Freight 12 awg 50 ft OEM ends
7) Various cheap orange cords 14 awg and 16 awg with OEM ends and some with aftermarket ends.

My rough findings are this.
The only three OEM cords that did not get warm or hot was the: US wire extreme, Milspec Direct, and the Prime Bulldog Tough. The 12 awg HF cord got barely warm but it is new, i have no doubt with minimal usage the ends would be fatigued and it too would heat up.

All the cheap orange cords got warm and a few got very hot. The worst was my 14 awg 50 footer that has been well used. In all cases the cords got hot at the ends and was usually both male and female ends ( I expected the female ends to fail more). The 16 awg cord, excluding the ends, did not get hot at all. After letting one of the 16 awg cords run for 20 mins you could start to feel a difference in the actual cord temp not just the ends. It was barely warmer than the cords laying on the floor with nothing plugged in.

The Voltec cord was fine on the male end but the female end was getting warm.

None of the cords that had aftermarket ends on them, male or female, got warm.

One of the worst cords which was the 14 awg 50 footer. This one I actually stopped the test after about two mins because the female end was getting very hot so there was no use in continuing. I cut the ends off and replaced with Leviton aftermarket ends and retested. No temp change observed. Proving that in this cord it was in fact the ends causing the temp increase.

I tested several cords since this experiment but they were all heavy gauge with aftermarket ends on them and none of them got warm at all. I didnt list them because one would expect 12 awg cords with good ends on them would not get warm and they dont.

I did this experiment to determine if it was necessary to run heavy gauge cords around the garage , less than 50 feet, or just use lighter cords with good ends. What I concluded is that if you use good quality ends, your probably in good shape even with some moderately heavy loads. For me , again < 50 ft , no need for 12 awg cords. A 14 awg cord with good ends will supply all the power i would use. If fact a 16 awg cord with good ends on it will cover 90 percent or more of what i need.

Outcome/ Summary
1) All cords that got warm or hot, did so at the ends.
2) I would not feel comfortable running much more than 12-13 amps, for any length of time, through a 16 awg cord regardless of the ends.
3) Be cautious when running large loads through cheap extension cords or ones with very used ends on them. Some of the cheaper ones that failed were not used all that much at all. The ends were not wore out. In fact the one was just about new so it leads you to believe that the ends are just not connected very well.
4) If i ever need to buy an extension cord, which i probably wont in my lifetime, I will most likely get SOOW 14/3 and put my own ends on it. This is definitely not the most cost effective though. Actually some SOOW 16/3 cords with nice ends would make great garage cords especially in very cold weather. Just be careful not to overload it. Many inexperienced people will see it and think it is thick so it must be heavy wire.

I realize everyone has different uses for cords and they may not be the same as mine. Some of my cords that failed and i cut the ends off of, you could probably use for another 20 years if your just running a drop light or something.

I just wanted to share my findings. Be careful guys when using old cords. The one that failed the worst, still got very warm even with the heater on medium which should only be 9 amps. For a 14 awg cord, it should have handled that easily.

I have a lot more detailed information in my notes about each test but dont want to type it all out here. If you have any specific questions, let me know.


Edited by jstutz (01/14/15 01:06 PM)

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#3600037 - 01/14/15 01:10 PM Re: Some Extension Cord Testing [Re: jstutz]
HerrStig Offline


Registered: 08/24/11
Posts: 9560
Loc: Boston, MA
Shore power cords for marina use are very well made.

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#3600058 - 01/14/15 01:47 PM Re: Some Extension Cord Testing [Re: jstutz]
Lapham3 Offline


Registered: 12/23/13
Posts: 849
Loc: Minnesota
Nice work-something to think about. I like to use 12 gauge and generally will replace the moulded after not long and with 'difficult' contact mating plugs with decent screw together.

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#3600067 - 01/14/15 01:57 PM Re: Some Extension Cord Testing [Re: Lapham3]
jstutz Offline


Registered: 10/06/08
Posts: 1556
Loc: NC
Originally Posted By: Lapham3
Nice work-something to think about. I like to use 12 gauge and generally will replace the moulded after not long and with 'difficult' contact mating plugs with decent screw together.


Yep your probably safe. Most of the ends i have are the 10 dollar Hubbell Industrial or the 5 dollar Leviton ends(reasonable price and good quality). Like the one in the link

http://www.homedepot.com/p/Leviton-15-Am..._-100011602-_-N

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#3600242 - 01/14/15 04:47 PM Re: Some Extension Cord Testing [Re: jstutz]
eljefino Online   content


Registered: 06/15/03
Posts: 32640
Loc: ME
I have a pricey 10 ga "Yellow jacket" cord that I cut perfectly good ends off of so I could use 220 plugs for my welder.

This bugger does everything right, and the insulation gets stiff in the cold but not unbearably so.

You could repeat the test with a power strip on the heater end and take voltage readings so you can see for sure how things drop off with use.

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#3600246 - 01/14/15 04:54 PM Re: Some Extension Cord Testing [Re: jstutz]
Rick in PA Offline


Registered: 01/04/03
Posts: 3203
Loc: Southeastern, PA
One thing I to do with screw terminal connections is a tightening sequence. I'll tighten the screw, back it off, tighten the screw, back it off, tighten the screw, etc... I find that in each cycle the screw turns just a little bit more. I'll do this until the screw tightens at the same place a couple of times. That way I believe I've formed the copper conductor to the connection as best as possible and I trust the connection will stay secure.
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#3600336 - 01/14/15 06:58 PM Re: Some Extension Cord Testing [Re: Rick in PA]
jstutz Offline


Registered: 10/06/08
Posts: 1556
Loc: NC
Originally Posted By: Rick in PA
One thing I to do with screw terminal connections is a tightening sequence. I'll tighten the screw, back it off, tighten the screw, back it off, tighten the screw, etc... I find that in each cycle the screw turns just a little bit more. I'll do this until the screw tightens at the same place a couple of times. That way I believe I've formed the copper conductor to the connection as best as possible and I trust the connection will stay secure.


Good idea, I may steel that technique from you.

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#3600351 - 01/14/15 07:17 PM Re: Some Extension Cord Testing [Re: jstutz]
Donald Offline


Registered: 03/21/04
Posts: 20459
Loc: Upstate NY
Why don't you cut apart the molded ends and see where the weak link is?
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#3600369 - 01/14/15 07:28 PM Re: Some Extension Cord Testing [Re: Donald]
jstutz Offline


Registered: 10/06/08
Posts: 1556
Loc: NC
Originally Posted By: Donald
Why don't you cut apart the molded ends and see where the weak link is?

Good idea, maybe this weekend ill cut apart the really bad one and see what is going on there.

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#3600461 - 01/14/15 09:23 PM Re: Some Extension Cord Testing [Re: jstutz]
JHZR2 Offline



Registered: 12/14/02
Posts: 41789
Loc: New Jersey
Originally Posted By: jstutz
I have a radiator heater that draws 1500 Watts on high which at my household voltage of 123V is 12.2A continuous. Run the heater on high for 5 mins through each cord and observe where the heat is generated and how much of it. I didnt go as far as to measure the temp with a thermometer but just touch and note if it is cool, warm , hot ect.


I think this is an interesting test.

Here's why... Ohm's law first...

Voltage (E) = Current (I) * Resistance (R)
Power (watts) = Voltage (E) * Current (I)

You dont really have a 1500W heater. You have a heater with a certain resistance.

If it was rated at 110VAC, then it is an ~8 Ohm heater. If it was rated at 120VAC, then it is an ~9.6 Ohm heater.

Let's assume it is a 9.6 Ohm heater. So at 123V, it was dissipating 1575W through the flow of 12.8A

But, the cord has some resistance too, which adds series resistance overall. So the 9.6 Ohm heater may really be a bit higher.

The resistance per meter for copper wire is:
12 AWG:0.00521 Ohm/m
14 AWG:0.00829
16 AWG:0.0132

Thus, the resistance for the cords is approximately:
1) .06 Ohm
1) .03
1) ?
1) .07
3) ?
1) .18
7) ?

A 14 AWG 50-ft cord that you said was the worst would be 0.3 Ohm.

All these values will be higher because the resistance of the connections is not included.

So a 9.9 Ohm effective load for that worst one would move 12.4A versus 12.8A if the load was just the 9.6 Ohm. The heat generation in the cord is I^2R, which is 153*0.3=46.1W dissipated in the cord, plus the higher resistance ends.

Compare that to the HF cord which would effectively dissipate around half that, since the lower resistance would mean higher current flow (bigger I^2 term) but lower resistance.

So its a balance between lower current flow at a given voltage, and higher I^2R dissipation.

And the ends will only make this worse if they are indeed a real issue.

Good test. It would be interesting to use a good multimeter and take a cord apart and identify the series resistance of the parts. Its easy to calculate then the actual heat dissipated and what it practically means to your observation (since stuff made of conductive metal moves heat away pretty well.



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#3600471 - 01/14/15 09:35 PM Re: Some Extension Cord Testing [Re: jstutz]
Merkava_4 Offline


Registered: 01/30/07
Posts: 17501
Loc: Clovis, CA
Originally Posted By: jstutz
The only three OEM cords that did not get warm or hot was the: US wire extreme, Milspec Direct, and the Prime Bulldog Tough.


What was the AWG size of the U.S. Wire Extreme?

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#3600510 - 01/14/15 10:15 PM Re: Some Extension Cord Testing [Re: jstutz]
spasm3 Offline


Registered: 05/30/10
Posts: 8662
Loc: North Carolina
I've always questioned if it really helps to use 12g extension if the home is wired in 14g?
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#3600526 - 01/14/15 10:42 PM Re: Some Extension Cord Testing [Re: spasm3]
JHZR2 Offline



Registered: 12/14/02
Posts: 41789
Loc: New Jersey
Originally Posted By: spasm3
I've always questioned if it really helps to use 12g extension if the home is wired in 14g?


Good point. But notionally, the use of an extension cord could double the run, or at least lengthen it in a non-trivial manner.

I would assume that in homes where the run is really long (like a big ranch house where the panel is in a garage and a big load is on the far other side, or something like that...), that the voltage drop evaluation would consider increased wire size to account for drop at a given ampacity.

Of course, builders do things cheap...

But I also think that 14ga is also being delegated more and more to just lighting circuits... with 12ga minimum for actual outlets.

If the average new home is 2600 sq ft, let's say that this means roughly 30x45' per floor for a two story home. That means that a run could easily be 50' from a panel to an outlet.

But the extension cord just doubled the length. Thats a big increase... in something that is going to have higher resistance due to age, strain, connections, etc.

Of course, that's also a reason why most stuff is rated for 110 while we see 120 at the wall, I guess.

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#3600655 - 01/15/15 07:03 AM Re: Some Extension Cord Testing [Re: spasm3]
kschachn Offline


Registered: 12/26/05
Posts: 9412
Loc: Upper Midwest
Why? It really has little to do with the gauge of the house wiring and everything to do with the length of the extension cord. You are correct in that if it is a short run then there is no reason to use a 12 gauge cord on a 15A branch circuit. But if the run is long then yes you would IAW the voltage drop you will see with the cord. Most cords have a chart on them showing the run length and voltage drop, but f not then that is easily available online. You will still never be able to pull more than 15 amps on that branch circuit, but if you have a long extension cord you will see excessive voltage drop with a thinner cord.

Extension cords aren't for the most part about the circuit they are attached to, they are about the expected load and cord length. Sure, you would need a 12 gauge cord on a 20A branch to pull 18A, but even then you have to watch your length. You might need a 10 gauge cord if the length is long enough (and the load is high enough).

Originally Posted By: spasm3
I've always questioned if it really helps to use 12g extension if the home is wired in 14g?
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#3600692 - 01/15/15 07:54 AM Re: Some Extension Cord Testing [Re: Merkava_4]
jstutz Offline


Registered: 10/06/08
Posts: 1556
Loc: NC
Originally Posted By: Merkava_4
Originally Posted By: jstutz
The only three OEM cords that did not get warm or hot was the: US wire extreme, Milspec Direct, and the Prime Bulldog Tough.


What was the AWG size of the U.S. Wire Extreme?


Sorry, dont know how I missed this. it is 14 awg.

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