Measuring 12 AWG cable for resistance (HELP!!!) - Page 1
Forum section: electronics / testgear

author: SharpEars
author_rank: Unknown
timestamp: August 02, 2015, 09:27:56 pm
content: I just received a stranded 12 AWG cable from China in the mail. I can't understand why its resistance is so high. The first question you will ask is, "How do you know its resistance is way too high?"So, here is what I did:I confirmed that the cable is definitely made of tin plated copper and not Copper Clad Aluminum (CCA) (Tested with a lighter, which melted off the tin to reveal the copper underneath a single strand.)The cable geometry is 65/30 (65 strands of 30 AWG wire).The resistance I am measuring is 0.01121 ohms per meter. This is way too high for 12 AWG copper stranded cable with a 65/30 geometry.The cable diameter is in fact consistent with 12 AWG (2.48 mm diameter for all strands as bundled).Here is how I measured the resistance of 0.01121 ohms per meter. I double checked this resistance several different ways:I took a 4-wire kelvin measurementI used two HP lab power supplies current reading (1 A)I used a Fluke 8842A to measure the current to confirm (1 A)I used a calibrated HP 3456A to measure voltage to confirm 0.0588 V at 1 ABottom line, the cable is 0.01121 ohms per meter, 11.21 ohms per km, 3.41695 ohms per 1000 ft.Now, let's get to the bottom line:WTF? The cable's resistance is twice as high as it should be! What could possibly be causing this?

author: georges80
author_rank: Frequent Contributor
timestamp: August 02, 2015, 09:47:19 pm
content: How are you 'connecting' your test equipment to each end of the cable?Unless you have a GOOD crimped lug or soldered the strands together how are you ensuring that each strand is carrying it's equal share of current? Or are you just relying on the strands 'touching' each other?cheers,george.

author: amirm
author_rank: Regular Contributor
timestamp: August 02, 2015, 09:48:43 pm
content: I tested a bunch of 12 gauge wires (seehttp://www.whatsbestforum.com/showthread.php?14134-When-12-Gauge-Wire-is-not-12-Gauge!) and arrived at similar results on a couple of spools I bought:And here it is graphically using Belden as the reference:The Fry's and BestBuy's home brands have similar DCR to what you measured. Instead of investigating why, I just avoid them.

author: SharpEars
author_rank: Unknown
timestamp: August 02, 2015, 10:04:13 pm
content: Quote from: georges80 on August 02, 2015, 09:47:19 pmI am using an alligator clip at each end of the 5.24 m cable under test. So, I guess I am relying on each strand touching each other in the end, but the alligator clips to come in contact with at least the outer strands of the cable.Would you recommend perhaps soldering the strands at each side into a single cylinder and then connecting the alligator clips to the soldered ends?

author: SharpEars
author_rank: Unknown
timestamp: August 02, 2015, 10:15:45 pm
content: Quote from: amirm on August 02, 2015, 09:48:43 pmI am getting 3.417 mOhms per foot. From the cables in your table, I happen to own the Monoprice 12 AWG speaker cable, which I have about 95 ft of remaining.

author: georges80
author_rank: Frequent Contributor
timestamp: August 02, 2015, 10:28:55 pm
content: Quote from: SharpEars on August 02, 2015, 10:04:13 pmI wouldn't trust just a clip on each end to make consistent contact across all the strands. Just a bit of oxidation on the plating and you have a measuring issue. A good quality crimped connector would be the a better choice. Soldering the strands at the end to connect them together would be ok.Consider that each strand carries a part of the current. The resistance of each strand is in parallel with every other strand. But, if you have poor contact from you clip and between strands then you will get inconsistent results.Then of course there's the variable of out of spec (lies and more lies...) cheap cable as per amirm's measurements (assuming he made GOOD contact to each strand at both ends of the cables under test).cheers,george.

author: SharpEars
author_rank: Unknown
timestamp: August 02, 2015, 10:52:22 pm
content: Quote from: georges80 on August 02, 2015, 10:28:55 pmSoldering the strands together made no difference. After soldering all 65 strands at each tip of the cable, I am getting exactly the same results, proving that the current was in fact traveling across all of the strands (equally).On the lies, lies and more lies front. I did make sure that there are in fact 65 strands of gauge 30 (assumed, but not measured) for a typical 12 AWG stranded configuration. I also made sure that the inner diameter (i.e., the diameter of the wires themselves) was 2.48 mm, which is correct. I also made sure that they are in fact copper strands by heating all of them with a lighter. Aluminum typically deforms at high temperatures rather quickly, while copper maintains its shape even when orange hot.

author: SharpEars
author_rank: Unknown
timestamp: August 03, 2015, 01:21:20 pm
content: Quote from: amirm on August 02, 2015, 09:48:43 pmSince I have that Monoprice 12 AWG speaker cable your reviewed, I compared a foot of it to the 65/30 tinned copper cable I received from China. The 65/30 measured 33% more resistance than the Monoprice, even though the Monoprice looked much thinner (more like 14 AWG than 12).I just don't get it! It seems to be composed of real tin plated copper strands. It is the right diameter. It just measures something awful on an ohm meter. There has to be an explanation. One thing I noticed is that the strands are not tightly wound inside the insulator, more like straight than a wound geometry, so perhaps there is not as good contact between individual strands. On the other hand, I soldered the tips for my test to make sure current is passing through all strands, but that did not seem to make any difference in the measurement.

author: georges80
author_rank: Frequent Contributor
timestamp: August 03, 2015, 05:32:21 pm
content: Copper composition from company A could be different to that from company B.Don't assume the copper has the same 'purity'...cheers,george.

author: SharpEars
author_rank: Unknown
timestamp: August 05, 2015, 12:40:32 am
content: Quote from: georges80 on August 03, 2015, 05:32:21 pmHow do you use copper that is so impure that the resistance is twice as much? I think what I purchased isn't tinned copper. It is tinned "some other metal alloy that looks like copper and passes the flame test."

author: ywara
author_rank: Contributor
timestamp: August 05, 2015, 01:52:12 am
content: Copper is expensive. Looking at the weights in amirm's spreadsheet, it's pretty clear what they are skimping on to get such poor resistance.

author: edavid
author_rank: Super Contributor
timestamp: August 05, 2015, 02:22:19 am
content: Maybe it's copperweld. Is it magnetic?

author: SharpEars
author_rank: Unknown
timestamp: August 10, 2015, 06:03:37 pm
content: Quote from: edavid on August 05, 2015, 02:22:19 amNo, it is non-magnetic (i.e., not copper plated steel). This is the first thing I tested.

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: August 10, 2015, 07:59:24 pm
content: If the copper contains a large fraction of recycled metal, and subsequently hasn't been through the proper (expensive) electrolysis refining step, then the DC resistance can easily be much higher than properly refined copper.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 10, 2015, 08:22:01 pm
content: Refer tohttps://www.nde-ed.org/GeneralResources/MaterialProperties/ET/Conductivity_Copper.pdfIt shows more than 10 to 1 variation in resistivity for various alloys and heat treats of copper.

author: SharpEars
author_rank: Unknown
timestamp: August 10, 2015, 08:50:58 pm
content: Quote from: CatalinaWOW on August 10, 2015, 08:22:01 pmWow, I did not know that. It seems that the Chinese are bilking us by using some seriously crappy copper (or an alloy) then.I am getting 50% conductivity of a proper 12 AWG stranded wire. I wonder what kind of crap they made their wire from.Lesson learned:Never buy wire/cable from AliBaba or AliExpress!

author: retrolefty
author_rank: Super Contributor
timestamp: August 11, 2015, 01:42:11 am
content: Quote from: georges80 on August 03, 2015, 05:32:21 pmNo wonder the audiofools will spend $100s for special low oxygen interconnect, power, and speaker cable.

author: SharpEars
author_rank: Unknown
timestamp: August 11, 2015, 03:01:23 am
content: I just received my 14 AWG cable, which was the polar opposite quality wise.I have posted a complete review in this thread:I want to praise an Ali Express Cable Seller

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 11, 2015, 04:55:45 pm
content: In most applications I wouldn't be too concerned about the copper resistivity. Battery cables being one of the exceptions. Even there it might not be appropriate to say the Chinese are "ripping you off". If you paid the same price for the Chinese cable that you paid for a low resistivity cable, or if you bought based on a resistance spec you could say you were ripped off, but it seems to me that you got what they advertised.As to audio applications - maybe for some high power systems it makes a discernable difference, but even there I would select an 8 gauge wire of random copper over a 12 gauge one made of gold plated oxygen free copper. Most audiophools I have dealt with are buying buzzwords more than they are buying performance. Maybe I should say all audiophools. The audio purists who make extreme decisions for technically sound reasons are not really audiophools.

author: SharpEars
author_rank: Unknown
timestamp: August 12, 2015, 04:54:51 pm
content: Quote from: CatalinaWOW on August 11, 2015, 04:55:45 pmI am using this for power carrying capacity (in a power supply build). I was told 680/0.08 geometry (and got 65/.25) and the resistivity was not quoted but implied based on geometry. So, I was very much ripped off...

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 12, 2015, 10:29:42 pm
content: Quote from: SharpEars on August 12, 2015, 04:54:51 pmYou've added information. The stranding was different than you were told. A rip-off. If they also told you that it conforms to ASTM B33 or some other similar standard then they also ripped you off on resistivity. I did a quick web search and found a variety of listings for 12 gauge wire. A surprising number did not even mention the material used in the wire. Others used generic descriptions like "copper" or "aluminum". The vast majority did not mention stranding configuration. A small minority claimed compliance with standards on wire. While my quick survey is in no way a statistically valid sample, it at least indicates the range of what is out there. If it isn't nailed down in writing you are vulnerable to the dishonest and also the ignorant. Those who can honestly say I didn't know there were different copper alloys, or specifications on wire. The ignorant and stupid far outnumber the dishonest. Is it a rip off when someone isn't trying to cheat you?

author: SharpEars
author_rank: Unknown
timestamp: August 13, 2015, 01:55:24 pm
content: Quote from: CatalinaWOW on August 12, 2015, 10:29:42 pmDefinition of dishonest:I show him a picture showing that the 680/0.08 cable he sold me is 65/.25 (the picture clearly shows all 65 strands, well at least 90-95% of them individually).He tells me that in China only 680/0.08 cable is made, so it couldn't possibly be. That is the definition of dishonesty, right there.Then, when I tell him that not only does my picture clearly show 65 strands, if I put 4 of them next to each other the total width equals 1 mm (i.e., they're .25 mm diam. strands, not 0.08 mm). Do you know what his reply is? He asks me, "But in America don't you have different mm?"At this point, I don't know whether this guy is playing moron or he is a complete (dishonest moron).I then tell him that 680 in China does not equal 65 in America and proceed to ask him whether he has one hundred fingers on his hands, because maybe in China you have a different number of fingers.

author: johansen
author_rank: Super Contributor
timestamp: August 14, 2015, 07:11:33 am
content: my boss bought some servers and they came with Chinese IEC power cords that measured 10 ohms. yes, you read that correctly.we disassembled them and found what almost looked like brass wire, and very little of it. so its possible they threw enough zinc or aluminum in the pot to dilute the copper.

author: TheBay
author_rank: Unknown
timestamp: August 14, 2015, 10:34:01 am
content: This thread is very interesting! I have a new Naim setup with an Arcam DAC etc.I have never been a cable whore and bought/made interconnects, speaker cable based on the type of cable, resistance etc. I have never actually measured any of these cables! I just went by the specs and as long as it was electrically compatible on the sheet, I.e. Resistance and Capacitance I used it.I used to laugh at those buying expensive cables, but I may have to eat my words after reading all this!Quote from: 3roomlab on August 14, 2015, 12:50:33 am

author: SharpEars
author_rank: Unknown
timestamp: August 14, 2015, 12:18:36 pm
content: Quote from: TheBay on August 14, 2015, 10:34:01 amNo, continue laughing at them! The only thing you need is a cable made out of decent copper, which is still for cables all the way to 14AWG less than $1 per meter. Cryo cooling it or having it blessed by a minister of Jesus doesn't change its electrical properties one bit.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 14, 2015, 06:16:12 pm
content: There are a number of standards for wire and cable, including copper wire. The price to purchase copies of these standards is a little daunting for those who have only casual need for them. If you work for a large corporation or have access to an appropriate library you may be able to get access at little or no cost.Some insight into the standards can be obtained from free sources. One which has a great deal of information is the Standard Wire and Cable Company catalog, which is available at:http://www.standard-wire.com/downloads/swc_catalog.pdfThere are a number things of interest in this catalog, including Page 1 where they say they offer wire and cable in a variety of metals and high strength alloys - followed by a listing of a dozen or more standard items.A little googling will get you other sources and links to the official standards should you choose to buy them. Note that there are several, depending on what your application is, and what laws apply where you live.

author: SharpEars
author_rank: Unknown
timestamp: August 14, 2015, 06:39:58 pm
content: Quote from: CatalinaWOW on August 14, 2015, 06:16:12 pmPage 261 of that linked PDF has some good resistance info for tinned copper wire...Thanks

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 14, 2015, 07:12:42 pm
content: Another interesting link on this general subjecthttp://www.tatsuta.com/products/equipment/

author: SharpEars
author_rank: Unknown
timestamp: August 15, 2015, 02:08:02 pm
content: Quote from: 3roomlab on August 14, 2015, 09:27:33 pmI did just that, hencemy threadnaming the AliExpress seller who sold me the 14 AWG cable, the cable's exact specs and other "review type" info for anyone else looking for 400/0.08 14 AWG silicon tinned copper cable that is:Priced dirt cheapOf high quality (good silicone insulation, low resistance, correct geometry)Not everything on AliExpress is a ripoff, so when you do find that diamond in the rough, post details about the seller/item so we, your fellow eevblog members can take advantage of it too!I certainly helped numerous people out looking for cheap flexible 14 AWG cable of very good quality with my detailed review.