Testing Extension Cords/Outlets

[MrAl]

Hi again,

Yes that looks like what i was thinking about. First time i saw one of those in years now
Thanks for the link. Fairly inexpensive too and widely available.
That thing and a square box and romex cable clamp would make a nice heavy duty extension cord. What is particularly nice is that it is then EASILY repairable, unlike most other extension cords. Most likely we'd just have to replace the two duplex outlets, and maybe the plug at the other end at some point. Use nice heavy gauge wire too.

 

[KeepItSimpleStupid]

Don't use a romex cable clamp. Try to use a real cord grip.

If your cord is flat use one of these: https://www.sealconusa.com/inserts-romex.html

Depending on what your objective was, you could put "feet" on the box, "bondable teflon" or felt.

 

[MrAl]

Hello again,

Yes you are absolutely right: a romex cable clamp is not a good idea, as that would squeeze the cable by an unknown amount and possibly hurt the internal wire insulation. Something that causes some pressure but more of a zig zag in the wire would be better. I'll look into this too.

Yes feet, arms, legs, eyes, nose, mouth, ears, hair, and of course we can not build anything today without putting in at least one LED

Hey a switch would be nice too.

 

[KeepItSimpleStupid]

Wire cage clamps are the ultimate stress relievers. The more you pull the tighter they get.

A bondable teflon bottom means they wont scratch when dragged upright, so you could use it on a hardwood floor.

 

[KeepItSimpleStupid]

These **broken link removed** are the ultimate grips at the ultimate price. I have a reall sall one that has an eye for pulling ethernet, telco and TV cables. I think it cost me about $20.00 when I bought it. Taping a string just doesn't work sometimes.

Some very high end stuff https://www.zoro.com/cep-cep-power-distribution-boxes/g/00062422/ not considered to be an extension cord, but "Temporary power distribution"
So, you get feet, handles etc.

 

[MrAl]

Hi again,

I am not sure what you are linking too there, in the first link, and the second link seems very expensive?
I would be staying near the low end pricing of the market products, like 3 dollars (USD) max for some cable clamp or whatever. I can get a somewhat cheap surge power strip for about that, and modify, and they have some means of cord relief built into the strip already. So maybe 3 bucks or so. For the whole socket with clamp maybe more, like 5 to 8 bucks or something like that, if it is good quality.

BTW the new fix with the $5 somewhat high quality socket worked out nicely so far. Testing has shown barely any temperature increase even after four hours on a hot day (85 degrees F). I also noticed that the cheapie extension cords (1.49 USD) dont even get hot, unless maybe the socket or plug end is faulty, and they are only 16 gauge wire.
Funny thing is i see 100 foot extension cords made with only 16 gauge wire. What the heck do they use these for, far away night lights?

I also just realized that i am approaching 10,000 post messages here on ETO. Wow, times flies when you're talking about something you are interested in.

 

[cowboybob]

Don't overlook the female (receptacle) side of this issue. Over/under sized feed wire (<10ga or >14ga), and less than secure feed wire attachment, especially if the "shove it in the hole" (as opposed to screwed down) method was used. Several areas that are prone to high current resistive heating.

 

[Tony Stewart]

What's All This Stuff About Extension Cords, Anyhow?

Seems like a lot of work for 1 cord.

Since the target load plug resistance is half of the problem for contact resistance and self heating, it is hard to compare test results, considering all the variables of aging , contact materials, geometry and plugs used.

The worst plugs are smooth solid spade plugs without the hole do not wipe the oxide off cheap receptacle contacts and have little friction for retention and thus can make the receptacle heat up. But they may cause less plating removal.

 

[MrAl]

Hi Tony,

Well i started testing extension cords, not just one be several, and i also had some over the years that got hotter than others too and so i decided to look into it a little.

Yes the plug end can contribute, but if the same plug is plugged into two different cords and one cord heats up and the other doesnt, i tend to believe that the one that does not heat up is better than the other for some reason. I also wanted to find out the reason.

This one cord however was not a cheap cord, but had decent wire inside and looked and felt pretty rugged. But that's the one that got the hottest on the receptacle end. This got me wondering how a good cord can go bad like that, even after hardly being used. I could see it if it was used so much that the contacts were getting worn, but this was hardly used.
What it looks like in the end is that the plastic that makes up the socket end is made of such thick plastic that it does not allow the contacts inside to cool off fast enough for the small but non zero amount of heat that they produce normally. Other cords i have tested are much cheaper ones, and they dont get very warm.
Would that better cord eventually fail? Maybe not, but i would rather have cool cords if it is possible, and with a better socket end it is possible so now it is just as cool as the others.

So it has been a bit of an adventure with a nice ending, although i had to ditch the original three socket end for a single socket replacement end.

 

[KeepItSimpleStupid]

Mr Al:

I try to bring everything to the table, expensive, cheap whatever. It's OK to throw ideas out. It's not OK to totally reject them in the beginning when it' "on the table" so to speak. You don't have to "eat it" or use it.

Hospital grade and/or high abuse receptacles are also available. In one work set-up the wiring was all hospital grade right angle 120 V plugs. A step down from twist-locks.

My mentality, it generally to fix it for good. I like antique stuff and I;d like it to last longer. I use a fair amount of those duplex to 6 outlet things that crew into the outlet. Call them socket savers, if you will. They get replaced periodically.

The long extension cords primarily are for yard work. They are followed by a 25' flexible cord because the other cord won;t fit the strain reliefs (wrap the cord) on the trimmer. If they are lucky, the hedge trimmer blade won't find the cord. They are also too heavy for the 6" cord on the circular saw or chain saw.

I, like Tony, don;t like the "stab in the back" contacts on receptacles. I use Ideal Term-a-nuts. with a little more work "up front", replacement of an outlet becomes super simple and you could easily do it live. In one case, a broken outlet can break a series set of wired receptacles.. In the other, the receptacle is independent.

 

[MrAl]

Hi again,

Tony:
I forgot to mention that i also wanted to discuss testing of the extension cords because i see on the web many sites that use an Ohm meter, which can not truly test the thing because it can not put out enough current. I was hoping to put forth a little information about testing them with a test that is much more suited to the way they work, or should work anyway.

KISS:
I like that way of thinking. For myself, i shop somewhere in the middle where i dont like to get the cheapest thing out there (because it wont work well) but also dont want to get into too much debt over something as simple as this. So i will usually buy something between cheap and expensive, but of course only if it looks like it is made good.

 

[Akash Doshi]

Very Nice Stuff...thanks for sharing reference links...

 

[Tony Stewart]

From my past Test Eng experience a typical cable test with automated cable testers ( e.g. CIRRUS) is 100mΩ max, with 1kV HiPot for any cable or harness.
Test time ~1s.

 

[cowboybob]

Very Nice Stuff...thanks for sharing reference links...

Welcome to ETO, Akash Doshi!

 

[MrAl]

From my past Test Eng experience a typical cable test with automated cable testers ( e.g. CIRRUS) is 100mΩ max, with 1kV HiPot for any cable or harness.
Test time ~1s.

Hi Tony,

That sounds good too. I had time to test some of these thoroughly so i let them sit for a while in free air at room temperature to see how hot they would get and where they got hot if at all. The results surprised me because i had assumed that the more expensive and sturdy looking cords would be better overall, which i found not to be the case. After fixing that one end though (replacing it with a quality socket end) it works well now, because that was the weak point in the design. The wire itself was good because it was a heavy enough gauge to handle the current, it was just the poor design of the socket part that killed the whole design. If they improved that, this would be a really high quality extension cord without any need for modification.

One significant point that came up here though was that resistance itself may not be a property of the cord that tells us if the cord is good or not, assuming a set of randomly chosen cords. For a randomly chosen set of cords one cord might be ok with 100mOhm while the next may not be. That's because heat is depending on resistance, while temperature is dependent on both heat AND dissipation factor.
For example, take a 100mOhm resistor and run 10 amps though it, what power does it try to dissipate. As we all know, 10 squared is 100 and that times 0.1 is 10 watts. Spread that out over 100 square inches and the power density is only 0.1 watt per square inch, which might show a temperature rise of 5 degrees C. Contain that within 10 square inches and that's 1 watt per square inch which means the temperature can go as high as around 67 degrees C or so.
So it partly depends where that resistance is located, physically. If it is over the entire length, that's great, but if like in my cord it is mostly in the CONNECTOR which is small to begin with, it gets hot. Since the connector is also insulated, that means it is not very good at dissipating heat.

In a plant where cords of the same type are made that could be different because that 100mOhm shows that it is the same as other cords of the same make, and at least some of them were already tested more rigorously and found to have 100mOhm short term resistance. If they all have 100mOhm then they are probably good. But for a randomly chosen cord, we have to be more careful im sure you agree.

 

[Akash Doshi]

Welcome to ETO, Akash Doshi!

Thank u COWBOY.... i also want to share some good reff for outlets..

 

[Tony Stewart]

Mr Al,
I agree.
If I were the test engineering mgr. at that factory, I would have an on-going reliability test (ORT) plan to include HASS which would test the product beyond limits, then isolate Root Cause , take Corrective Action on poor crimp design/process and lower test criteria to 3sigma upper limit of design such as 30 mOhm rather than 100 mOhm. Minimal time.
Testers would have replaceable contacts which were designed to last 10k cycles or more.