shielded twisted pair solid bare copper wire - Page 1
Forum section: electronics / general

author: guenthert
author_rank: Frequent Contributor
timestamp: February 01, 2023, 05:11:50 pm
content: preferably 18 AWG -- where would I buy such (small amount, say 30ft, not a whole 1000ft spool)? Perhaps even a place in the S.F. Bay Area?[thought about putting this into Buy/Sell, but the answers might be of wider interest -- at least among the voltnuts]

author: TimFox
author_rank: Super Contributor
timestamp: February 01, 2023, 05:20:00 pm
content: "solid bare copper wire" usually means uninsulated ("bare").You want to specify twistedinsulatedsolid (not stranded) copper wire, which is probably plastic insulated rather than enameled (as in magnet wire).18 AWG is kinda large for twisted solid wire, would be quite stiff.

author: guenthert
author_rank: Frequent Contributor
timestamp: February 01, 2023, 06:00:41 pm
content: Well, I was looking for pure copper, not the tinned cables one easily finds (and I suspect are used in networking, at least the smaller diameter ones). I think I saw one seller on eBay referring to such as 'bare', but he might be as clueless as I am.Stiff is fine by me, but a little smaller would suit as well. Not too small though, as then screw terminals can't be used anymore easily.

author: TimFox
author_rank: Super Contributor
timestamp: February 01, 2023, 06:41:07 pm
content: Solid bare copper wire is readily available, and insulated unplated copper wire is also readily available.The latter is what is normally supplied for power wiring inside buildings, but usually 14 AWG and larger.I checked my usual source for uninsulated bare copper wire,https://www.remingtonindustries.com/but all of their insulated wire seems to be tinned.They do have 14 AWG THHN solid insulated wire in reasonable spools, which I believe is untinned copper.You should be able to get that in arbitrary lengths at Home Depot, or in 25 and 50 foot spools in a few colors.Much smaller wire is used for Cat 5 and Cat 6 cables, some of which should be solid wire but at roughly 24 AWG.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: February 01, 2023, 07:07:41 pm
content: Search for bell wire and thermostat wire. The problem is going to be the shielding and the twist. If the length is short you can twist wires and put a braid over them. What are you trying to accomplish? That could make a difference in what people recommend.

author: guenthert
author_rank: Frequent Contributor
timestamp: February 01, 2023, 07:19:24 pm
content: Quote from: Conrad Hoffman on February 01, 2023, 07:07:41 pmYeah, Home Depot did find me thermostat wire, which I am unfamiliar with. Is that twisted? Shielded? From the pictures it didn't look like it would be. Elsewhere I found 'Fire Alarm' cable, which looked promising (actually, it isn't -- those alarm cables aren't twisted), but I found only large, expensive spools.Home Depot hashttps://www.homedepot.com/p/Micro-Connectors-Inc-250-ft-CAT-6-Solid-STP-Outdoor-23AWG-Bulk-Ethernet-Cable-Blue-TR4-560BLOU-250/312137589. A bit smaller diameter than I'd desire and still too large a spool, but almost there.I want to connect a Keithley Nanovoltmeter (181) (I'm planning to connect it directly to the amplifier inside, bypassing the weird Amphenol connector) to a Keithley 7064 low thermal EMF relays card.

author: TimFox
author_rank: Super Contributor
timestamp: February 01, 2023, 08:08:29 pm
content: I have made my own shielded twisted pairs withstrandeduntinned copper wire by adding shield braid around appropriate test lead wire, or test leads with banana plugs. Untinned stranded wire is easier to find than untinned solid wire (insulated) in these sizes.I usually put heat-shrink tubing at each end of the shield to hold it to the twisted wires.

author: Overspeed
author_rank: Frequent Contributor
timestamp: February 01, 2023, 08:57:20 pm
content: HelloBe aware of one detail : industrial copper is not the top specification low oxygen copper , and some '' chinese import '' are made incopperRegardsOS

author: TimFox
author_rank: Super Contributor
timestamp: February 01, 2023, 09:57:08 pm
content: Yes, normal copper wire is usually ETP copper, which can be mechanically harder than oxygen-free copper, but is still a good choice when you worry about thermal EMF.OFHC and OFE vacuum-melted copper, which are much more expensive, are very useful when you need to flex or bend the wires a lot, and will handle much more abuse before work-hardening and failing due to metal fatigue.They are also useful in vacuum, avoiding outgassing from absorbed oxygen, etc.There are also silly uses in over-advertised audio applications.

author: guenthert
author_rank: Frequent Contributor
timestamp: February 01, 2023, 11:47:04 pm
content: Yeah, I'm sure Belden happily sells therightcable, for a price. I'm an old miser though.While Home Depot has a promising candidate, I didn't want a whole spool. CentralComputers sells Cat7 network cables, which are shielded (STP). But are they unplated copper? Meanwhile I learned that copper cable is tinned not (just) for ease of soldering, but to make it resistant to humidity. So I guess cables meant for outdoor applications will be tinned and patch cables not necessarily. One way to find out ...Turns out, CentralComputers also have spools of network cables, but they were not interested in selling me a few feet (gosh, I miss WeirdStuff, Fry's and Halted/HSC now ...). They suggested that I get a patch cable and cut of the connectors. So I did, you know, for science.It's nicely shielded (each pair is shielded and all of them once more), I give them that. And it was unplated copper, sadly however tiny (AWG 26, I'd say) and stranded. Guess, the latter I could have figured by the ease of bending it. Oh, well, I needed a cable for a RS-485 connection anyhow ...

author: TimFox
author_rank: Super Contributor
timestamp: February 02, 2023, 12:04:11 am
content: The only thing I can suggest, if you want AWG 18 untinned solid copper wire formed into a shielded twisted pair is the following:1. Buy a small roll of AWG 18 solid bare copper wire from Remington (see link above) or other reputable vendor. Remington stocks AWG 32 through AWG 14; 25 ft of AWG 18 costs $12.06.2. Cut two lengths of that wire appropriate to your requirement.3. Insulate each length with polyolefin heat shrink tubing, and shrink to fit.4. Grab one end of both wires in a vise and twist them together, using a hand-operated drill (not power).5. Shove that assembly into a length of shield braid.6. Add a short length of "regular" insulated stranded wire at each end of the braid: strip off about an inch, wrap around the braid, then cover with larger heat-shrink tubing, to give the shield connection.Leave a reasonable length of unshielded wire at each end, to fit your requirement.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: February 02, 2023, 12:23:14 am
content: If you're connecting to a nanovolt meter, there's almost no current flowing, so why the need for any particular gauge? Why the need for solid wire? If you've ever stripped back very old untinned wire, it's not pretty, in fact it can react with the insulation. Look at old audio cables with high strand count in PVC; the wire is often green! I'd be making this out of 26 AWG silver plated wire with Teflon insulation, built as described above. Or, medium fine enameled magnet wire. Bare when you scrape it!

author: guenthert
author_rank: Frequent Contributor
timestamp: February 02, 2023, 12:35:25 am
content: Quote from: Conrad Hoffman on February 02, 2023, 12:23:14 amTo quote the operations manual of the 7064 relays card:"2.3 Wiring[..]With a contact potential of less than 1uV from input to output, #18 AWG solid copper wires are recommended to minimize the effect of thermal EMFs."The twisting and shielding I deem necessary as there is just a lot of EMI here around. I could try w/o shielding, but w/o twisting it's unlikely to be fruitful.Quote from: Conrad Hoffman on February 02, 2023, 12:23:14 amConnection to the 7064 is made at the barrier strip terminals. The amplifier within the 181 uses screw terminals. For such solid wire is imho *much* easier to use. I don't care how the cable looks in several decades.

author: TimFox
author_rank: Super Contributor
timestamp: February 02, 2023, 02:59:49 am
content: I have also seen really crappy surfaces on fine stranded bare copper wires, such as in old power cords.Fine strands means lots of surface area, and the rubber in old power cords is far from inert.Is your EMI problem 60 Hz or RF?

author: Overspeed
author_rank: Frequent Contributor
timestamp: February 02, 2023, 09:15:38 am
content: HelloTelephone wire are 0.5mm2 and copper quality is average good , that available in staright or twisted pair in cable , usually that available from scrap company , recycling company or telephone company which have refuse in the binI use bit of them to make jumper on PCBRegardsOS

author: iMo
author_rank: Super Contributor
timestamp: February 02, 2023, 10:40:03 am
content: CAT patch cable would work fine, imho. There are 4+ pairs in the cable, use a pair as a single wire for your purpose. Those are shielded as well, stranded or solid.Be aware some solid CAT patch cables are made of copper-clad aluminum wire..

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: February 02, 2023, 11:01:19 am
content: I have access to old good coax, usually Belden RG 58, which may be kinked or otherwise unfit for RF.If you have a radio or CB shop nearby, they will probably have some as "junk" usually free.I think that 75 ohm TV cable is also good copper, lots of that stuff around.You can remove the shield or leave it on if it will fit.Some sensitive voltmeter measurements call for shielded wire

author: Overspeed
author_rank: Frequent Contributor
timestamp: February 02, 2023, 02:43:02 pm
content: HelloI agree and a major concern is corrosion for any copper or brass connector and connection . uncoated bare copper need a particular care and a dry storage up to a inert gaz storage .Contact resistance is also concernhttps://materion.com/-/media/files/alloy/newsletters/technical-tidbits/issue-no-06---the-importance-of-contact-force.pdfRegardsOS

author: guenthert
author_rank: Frequent Contributor
timestamp: February 02, 2023, 05:59:14 pm
content: Quote from: TimFox on February 02, 2023, 02:59:49 am60Hz is dominant (particularly when it's cold and my upstairs neighbor turns on his space heater), but most meters filter that out quite well. Problem are switch-mode power supplies with switching frequencies some 40kHz to 1MHz (does that qualify as RF?) which weren't so common when those old meters were designed. I'm sure there is high frequency stuff as well, but I cannot measure that and it's probably of low field strength (with the exception of cell phone perhaps, but I can at least keep my own away). Worst offender by a large margin is PowerLAN, which I have to turn off for the time I make measurements.

author: Overspeed
author_rank: Frequent Contributor
timestamp: February 02, 2023, 07:03:49 pm
content: HelloIn a lab that possible to built a '' non AC '' aera and using a faraday cage , no a size of a football stadium I have one of the size of a british telephone box I have resuse a surplus french telephone box which are in stainless steelhttps://hollandshielding.com/Mu-copper-faraday-cagesRegardsOS

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: February 02, 2023, 08:24:30 pm
content: FWIW, I use solid twisted pairs from phone wire for voltage metrology applications and it works very well. Easy enough to add shielding if you need it. I do clean the ends of the wires as needed.

author: Overspeed
author_rank: Frequent Contributor
timestamp: February 03, 2023, 09:47:17 am
content: HelloThis cable is a nice option as that possible to open it and recover two twisted pairs with shield or even use only one pair and let the cable as ithttps://www.belden.com/products/cable/electronic-wire-cable/multi-conductor-cable/83321eThe cable OD is under 5 mm so 0.2 inchRegardsOS

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: February 03, 2023, 11:06:03 pm
content: Anytime you have two metals in contact there is a Seebeck effect, which may affect your measurements.A little gold plating probably does not cause much effect thoughVery sensitive measurements should be with connections of same metal, in this case copperHere is a Quote:Thermal EMFWhen two, dissimilar metals are joined a voltage is created. This voltage is known as the thermal electromotive force (EMF) or the Seebeck voltage. The Seebeck voltage is dependent on the temperature of the junction and the composition of the metals joined. The specific metal-to-metal junctions result in specific temperature coefficients (µV/°C), also known as Seebeck coefficients. The following table lists the most common metals and their respective Seebeck coefficients.Junction µV/°CCopper-Copper <0.3Copper-Gold 0.5Copper-Silver 0.5Copper-Brass 3Copper-Nickel 0.5Copper-Lead-Tin Solder 1-3Copper-Aluminum 5Copper-Kovar 40Copper-Copper Oxide >500

author: TimFox
author_rank: Super Contributor
timestamp: February 04, 2023, 03:55:12 am
content: Note that copper-gold and copper-silver junctions have quite low EMFs, but copper-copper oxide is huge.Teflon-insulated silver-plated solid copper wire is readily available.

author: 1audio
author_rank: Frequent Contributor
timestamp: February 04, 2023, 04:32:00 am
content: I think the best available cable would be some long obsolete IBM Twinax: BELDEN | 9860 0101000 Before the surplus stors all vanished they probably had some. Solid conductors in a shielded cable will be really stiff so not to desirable usually. Search eBay for "IBM Twinax" to find some. Most examples will be stranded.

author: Overspeed
author_rank: Frequent Contributor
timestamp: February 04, 2023, 09:23:36 am
content: HelloCorrosion control on bare copper is a nightmare even in a lab , that why most high value applications use silver coated wire including aerospace domains .Focusing on copper only will not solve other problem as connector quality concerns and other as contact force / micro fretting / wear / surface roughness ...Devil is in detailsRegardsOS

author: guenthert
author_rank: Frequent Contributor
timestamp: February 04, 2023, 07:29:21 pm
content: Thanks all for the input. I begin to realize that this is a more niche application than I expected. And sure, if it were for a national lab I'd be on the phone with Belden and get a quote ...The Keithley 181 isn't all that sensitive though (specified for 30 count pk-pk noise within 2m on the 2mV range).Wrapping a shield on a twisted pair cable myself didn't cross my mind, I must admit. Meanwhile I considered cutting the isolation of previously mentioned Cat7 cable and slipping that mesh off it, but I doubt that is practical. Instead I just used the Cat7 as is (after cutting its connectors), reusing the Amphenol connector I had (*), i.e. soldering two pairs (one conductor of each) to its soldering cups. On the other side I soldered short (~1/2") strips of #20 bare copper to ease using the barrier strip terminals.I'm aware that those are now numerous unlike metal transitions, but the original Keithley connector with the copper pins is long unavailable and I have neither welding- nor crimping tool (and I can't crimp w/o proper tools, I tried). But since those are more or less symmetrical and in like temperature zones, it shouldn't betoobad.It turned out actually better than I hoped:

author: HalFoster
author_rank: Frequent Contributor
timestamp: February 05, 2023, 11:41:54 am
content: Markertek is a good source of by-the-foot cableshttps://www.markertek.com/category/bulk-cableHal

author: coppercone2
author_rank: Super Contributor
timestamp: February 05, 2023, 11:45:55 am
content: I buy twinaxial cable for this, its expensive though. Some are twisted and some are not.

author: Overspeed
author_rank: Frequent Contributor
timestamp: February 05, 2023, 03:31:29 pm
content: Helloan important factor is to have or to keep spare length of cable to be able to repair / update / renew , cable industries is not a place for some meters only so when a good cable is available whatever the cable is the best mthod is to purchase more and keep it in dry storage box for the futureRegardsOS

author: tkamiya
author_rank: Super Contributor
timestamp: February 11, 2023, 06:54:06 pm
content: OP can buy any wire he desires from Digi-Key by the foot. Per foot prices are much higher than bulk purchases but they are made available for any custom length.