how to twist large copper strands of wire together for crimping ? - Page 1
Forum section: electronics / projects

author: Kjelt
author_rank: Super Contributor
timestamp: July 04, 2018, 05:58:23 pm
content: Hi ,I am having trouble to braid strands of copper wire into a larger strand that I can fit into a cable shoe/lugThe strands are 2mm2 I have 16 of which I discard 2 so left with 14 strands of 2mm2and I just can not get them all into a 35mm2cable shoe (AWG2)I am twisting the strands with force and if I measure 10cm from the end it would fit with ease but at the end of the wire they won't nicely integrate.In the industry they can fit 35mm2wires in this cable shoe and I have problems with 28-30mm2I have thought about hardsoldering the 10cm from the end which is the right size, let it cool off, slide the shoe over it further, crimp and then cut the 10cm off but that is such a waisteDoes anyone have experience or know how this should be done?

author: alpher
author_rank: Frequent Contributor
timestamp: July 04, 2018, 06:47:25 pm
content: One ugly job you have there, my suggestion:do not try to twist the strands!Just cut the end square and slide in the ferrule.

author: CopperCone
author_rank: Super Contributor
timestamp: July 04, 2018, 07:31:01 pm
content: I think if you twist a crimp wire then you have sort of a force that wants to slide it out rather then just flatten, so its weaker

author: The Soulman
author_rank: Super Contributor
timestamp: July 04, 2018, 07:34:36 pm
content: By twisting you place the strands at an angle so in effect your strands get a bit shorter and therefore it gets thicker,and it be even thicker because of the individual misalignment of the strands.If you have tight ferrules don't twist at all just line them up straight and gently insert.Out of curiosity, why would you need 14 strands of 2mm2 into one connection?

author: CopperCone
author_rank: Super Contributor
timestamp: July 04, 2018, 07:41:27 pm
content: oh yea the thing is, the crimp is gonna have a rating for current. This depends on the interface size between the crimp body and the wire and the thermal properties of the interface.The wire gauge you can use for a lug crimp is going to have a higher ampacity then the crimp for chassis wiring. Check the rating to make sure.

author: Kjelt
author_rank: Super Contributor
timestamp: July 04, 2018, 07:43:23 pm
content: Well they are already in one strand but that was 70mm2.Then I bought 70mm2cable shoes, took out my AMP hydraulic crimpener and found out it can do max AWG2Quote from: The Soulman on July 04, 2018, 07:34:36 pmDon't laugh but I am going to use it to ground the vfd box, the motorcontrolbox and my cnc machine together. It is an EMC thing.Normally you'd use Litze of about 20-40mm2but I found these strands at the local scrapyard so I work with what I encounter

author: CopperCone
author_rank: Super Contributor
timestamp: July 04, 2018, 07:47:02 pm
content: http://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=82004_FASTON_TERMINALS_-_FULL_CATALOG&DocType=CS&DocLang=ENpage 8 has fastons. I don't know where to find the ratings for the eyelet ones. It is probably pretty high so long you torque it correctly.

author: Kjelt
author_rank: Super Contributor
timestamp: July 04, 2018, 07:51:22 pm
content: Thanks but for this application it is more a lowest impedance as possible connection than there are really large currents flowing. Its application is common grounding, yeah I know overkill ,but isn't that part of the fun. Iwill insulate with shrinktubing.

author: CopperCone
author_rank: Super Contributor
timestamp: July 04, 2018, 07:54:05 pm
content: I found it.http://www.farnell.com/datasheets/612666.pdfIf you look, the rating of the eyelet crimp will be very similar to the rating of the wire for chassis use. Within 90%.

author: The Soulman
author_rank: Super Contributor
timestamp: July 04, 2018, 08:01:14 pm
content: Quote from: Kjelt on July 04, 2018, 07:43:23 pmSounds plausible.

author: Ian.M
author_rank: Super Contributor
timestamp: July 04, 2018, 08:03:25 pm
content: Get the strands as straight as possible and seize them together in a bundle with a single strand of thin copper wire, rolling the bundle as you put on the seizing to get it as well compacted and circular as possible. Done with care, thin enough wire and with the seizing as tight as possible (just short of breaking the fine wire), the increase of diameter due to the seizing wire thickness should be less than the decrease due to better alignment and packing and straight strands.

author: jpanhalt
author_rank: Super Contributor
timestamp: July 04, 2018, 08:16:27 pm
content: +1 For Ian's comment. That is what I do for heavy cable.

author: Kjelt
author_rank: Super Contributor
timestamp: July 04, 2018, 08:36:33 pm
content: Ok I am interested but do not follow completely, a YT video or some pictures would be nice but that is probably a no go.So to verify i now have 14 strands of 2mm2and each strand A consists of around 20 wires 0,4mm diameter. These are all twisted. Now does that mean I have to unstrand all the 0,4mm wires so 280 wires and straighten them?Or can I use the 2mm2strands and straighten those?

author: Gregg
author_rank: Super Contributor
timestamp: July 04, 2018, 08:55:28 pm
content: A trick I have often used is to slightly bell the sleeve part of the lug to guide the wire strands in. The ring lugs are soft copper with tin plating so it doesn’t hurt them to slightly expand the neck. I clamp the ring part in a vise with soft jaws (two lengths of flat aluminum angle) insert a smooth punch a little smaller than the ID and roll it around by hand to bell the sleeve. A tapered punch can be used to swage the sleeve a bit if you are careful.As others have stated, just straighten out the ends of the wires enough to allow straight insertion which definitely has a smaller OD than twisted strands. I prefer a hexagonal crimp that tends to put less localized stress on the crimped strands.

author: jpanhalt
author_rank: Super Contributor
timestamp: July 04, 2018, 09:02:49 pm
content: Quote from: Gregg on July 04, 2018, 08:55:28 pmGood suggestion, maybe, if the lugs are not welded. The ones I use are welded. Welding helps with the crimp.EDIT: Sorry, I missed the "bell" part and thought you were talking about expanding the whole ferrule.

author: Ian.M
author_rank: Super Contributor
timestamp: July 04, 2018, 10:58:57 pm
content: Quote from: Kjelt on July 04, 2018, 08:36:33 pmIf you unlay the cable into 14 strands and lessen the twist of each individual 20ish wire strand, it *should* be good enough. However for ultimate best packing, then yes, you'd need to unlay the strands and straighten each wire for about three times the ferrule length and seize it for double the length then trim the end.

author: Gregg
author_rank: Super Contributor
timestamp: July 04, 2018, 11:00:11 pm
content: I did a little demonstration, here are the pictures:I kind of like leaving the crimp a little way from the end of the barrel to mitigate stress at the crimp but a hex crimp to the end will cover traces of the lug being belled in case some snooty inspector ever looks at it.

author: CopperCone
author_rank: Super Contributor
timestamp: July 05, 2018, 12:43:53 am
content: What is the method for testing if crimps are indeed gas tight? Is there a standard?

author: Kjelt
author_rank: Super Contributor
timestamp: July 05, 2018, 06:42:00 am
content: Thanks Ian and Greg,I will have another try at this with your suggestions

author: tpowell1830
author_rank: Frequent Contributor
timestamp: July 05, 2018, 12:13:08 pm
content: Okay, this is probably going to be an unpopular suggestion, as I once, in another life had to do such things. I like the idea of twisting the wire together because it helps prevent the bundle from buckling when you bend it.After twisting your wires together, cut the end square, and before you slide the terminal lug on, slide 2 (or 3, your choice) hefty, thick walled pieces of heat shrink onto the bundle (approximately 5 cm long), and after installing and crimping the terminal lug, slide the heat shrink over any of the remaining ugly frays and the terminal lug and capture them in the heat shrink and then you have a beautiful piece of work that is very functional.Another method that I don't use, but I have seen others do it, is to solder approximately 2 cm of the end of the bundle before installing the terminal lug. I don't like this method, but it does encapsulate all the frays.Hope this helps...EDIT: I do not recommend crimping the lugs on and then twisting the wire because this could cause the wires inside the crimp to: a. get stressed and possible break or b. shift inside the crimp, possibly causing a loose connection.

author: Kjelt
author_rank: Super Contributor
timestamp: July 05, 2018, 12:17:13 pm
content: Quote from: CopperCone on July 05, 2018, 12:43:53 amAFAIK they take samples eg cut some crimped cableshoes in the middle and check the consistency, there should be no gaps or spaces.Perhaps a high tech modern solution is to xray or ultrasonic scan the crimp, actually it is not that much different of inspecting the quality of welds I guess.

author: darrellg
author_rank: Unknown
timestamp: July 05, 2018, 05:52:37 pm
content: I would just divide the wires into smaller bundles and use multiple lugs.

author: Kjelt
author_rank: Super Contributor
timestamp: July 05, 2018, 06:34:47 pm
content: Quote from: darrellg on July 05, 2018, 05:52:37 pmAlso thought about that but in the end it comes down to if you use too little wires eg too big a lug so the insertion is easy you risk a bad crimp since the crimp should in the end create one single piece of solid metal, too little wire or too big a lug you end up with a bad crimp that could result in wires fallling out or oxydation.

author: C
author_rank: Super Contributor
timestamp: July 05, 2018, 07:12:12 pm
content: Actually I think you are doing it the hard way, Backwards.Just take you nice strait wire and then crimp them.Then put one end in vice and other in a drill and twist them.C

author: reboots
author_rank: Regular Contributor
timestamp: July 05, 2018, 07:49:30 pm
content: Is your goal to have the strands twisted within the crimp? And will all the strands fit into the lug without twisting?If so, you could install the lug over the untwisted wire; slide it in several cm; twist and trim the end; then slide the lug back out until the wire is positioned as desired, and crimp.This wouldn't be possible with insulated wire, but it should work with the bare conductors in your picture.

author: Kjelt
author_rank: Super Contributor
timestamp: July 05, 2018, 08:07:08 pm
content: Quote from: Ian.M on July 04, 2018, 08:03:25 pmYES! This was the golden tip.I untwisted 30cm the copper thin wire worked but slipped badly so I went to tiewraps and the diameter was just 0,3mm below the lug diameter.First try I only missed two single 0,4mm wires so more than good enough!

author: Ian.M
author_rank: Super Contributor
timestamp: July 05, 2018, 08:44:32 pm
content: Quote from: Kjelt on July 05, 2018, 08:07:08 pmCable ties tend to make a non-circular bundle so may actually make the job harder, however they are useful to stop the end unlaying any further.Start by taping the very end of the unlaid strands if they are difficult to keep all together. Next form aconstrictor knotin the fine wire (which may be tinned wire but must not be enamelled). Slip it over the unlaid end of the cable with the short end from the constrictor knot furthest from the cable end. Tuck the short end back under the constrictor knot so it lies parallel to the cable strands, but leave a loop. Work the knot up tight where you want the start of the seizing. Working towards the end of the cable, put on about ten turns as a whipping, work them up tight and follow them with a half hitch so it so they cant loosen. After the first group of ten, pull on the tail of the short end to get rid of the loop, then cut the tail flush with the cable end. Repeat putting on ten turns of whipping then a half hitch till near the end of the cable. When you get near the end, remove the tape and, working with a long loop, lay the end of the fine wire parallel to the strands leading away from the cable end, using the loop, put on another ten turns, and a half hitch, then work them up tight and pull the tail through till the long loop is gone.An alternative if there is very little clearance is to put on a plain whipping (no half hitches after the constrictor knot, and at the very end clip out a couple of wires from a strand to reduce the diameter for the last ten turns, and put them on working with a loop, over the fine wire end so you can pull the tail to lock them in place without increasing the diameter.If there is virtually no clearance, put on a whipping using whipping twine, waxed linen thread or waxed dental floss, starting from a constrictor knot but don't bury the tail. Tape the end of the whipping to hold it, but *DONT* lock it with a half hitch or bury it or do anything to secure it that cant simply be unwound. After trimming the end of the cable, slide it into the ferrule unwinding the whipping as you do so.

author: Kjelt
author_rank: Super Contributor
timestamp: July 05, 2018, 09:02:45 pm
content: Quote from: Ian.M on July 05, 2018, 08:44:32 pmYes I was looking for a hose clamp, if that is the right english term, it is a metal ring you can adjust the diameter by rotating a screw. Did not have one.QuoteWow thanks that is a very detailed description, I have to study on it esp with the english "knotting terminology" let me get back on that later

author: Ian.M
author_rank: Super Contributor
timestamp: July 05, 2018, 10:47:09 pm
content: Edit above: I left out a sentence about repeating the ten turns then a half hitch.If you have any problems with the terminology, I can attempt to explain any specifics.Even a hose clamp is problematic unless you put it on over a thick layer of rubber tape, as the part under the screw tends to dig in, and the band tends to kink as its tightened if you need more than a small reduction in diameter. A constrictor knot in thin nylon cord, braided fishing line, kite line or similar high strength thin cord is far more likely to result in a circular bundle, especially if you tightly tape the bundle first so the knot cant dig in easily. Tighten it using two spikes (a pair of stout Philips screwdrivers will do), wrapping each end of the line several times around the shank and holding the tail against the grip, then lever against two sides or ends of a solid block placed under the cable.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 05, 2018, 11:29:13 pm
content: If this is for EMC, you're not gaining much over a handful of hookup wires. It's good galvanic grounding, but not much better than spaghetti once you get up to some MHz (give or take length).For that, you really need metal boxes (grind off the paint where connections are made), metal connectors and conduits. Treat it like RF transmission lines, because, well, it always is. Conduits serve a particularly useful purpose: all the currents are gathered together within, and you can insert a line filter there, if you like (and if applicable). Do this for the mains wiring, and the control signals if they need it (preferably, they're isolated and aren't carrying much noise).Tim

author: Kjelt
author_rank: Super Contributor
timestamp: July 06, 2018, 09:16:07 am
content: Quote from: T3sl4co1l on July 05, 2018, 11:29:13 pmAll the machineboxes are Rittal full metal enclosures with mains filtering, I got two: one controlling the milling spindle (very noisy frequency converter) and one for the control and powering the motors. Then there is the target machine the CNC machine from aluminium profile on a metal stand. So the purpose of this cable is to connect the metal spindle box, the cnc machine and metal stand all together to the metal control box in order to get a star grounding and low impedance between all the parts. This would ideally be Litze but this will also be good enough (i hope).So your concerns are valid but addressed inside the boxes which is a bit offtopic.

author: Kjelt
author_rank: Super Contributor
timestamp: July 06, 2018, 09:18:02 am
content: Quote from: Ian.M on July 05, 2018, 10:47:09 pmThanks I am a vision person so a picture tells me 100 times more than words , so thank you for the knot website that was very helpfull.The ten turns are those on one spot so over eachother to fix or do you mean over a length of wire so kind of circelling, I am trying to visualize the end result.If you happen to have a picture of one of your previous cablefixes that would be great.

author: Ian.M
author_rank: Super Contributor
timestamp: July 06, 2018, 09:30:51 am
content: The turns go on flat and close spaced (touching side by side) as-if you were winding a helical tension spring. DO NOT let them pile up in one spot as that would stop it fitting cleanly into the ferrule.Unfortunately I rarely document the simple stuff photographically, and I'm fairly sure I don't have the right materials on hand to prepare an example as I don't currently have an offcut of fine stranded heavy cable, or suitable bare fine wire in stock. Also although I have a good mental 3D model of it, I cant draw in perspective well enough to convey it clearly.

author: Kjelt
author_rank: Super Contributor
timestamp: July 06, 2018, 09:43:07 am
content: Hi Ian,not a problem I will be experimenting, I got a good idea what needs to happen, almost there yesterday so confident I will get it going.For now I have some work to doSo it will probably be after the weekend I can have another go at it again.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 06, 2018, 12:00:45 pm
content: Quote from: Kjelt on July 06, 2018, 09:16:07 amCan you diagram this? Since as you say,Quote from: Kjelt on July 06, 2018, 09:18:02 amMy first instinct is, if everything alreadyismetal conduits, then what's the cable for? You still want a ground wire in the conduits and boxes, for safety purposes, but they're not there for RF purposes of course.Tim

author: Kjelt
author_rank: Super Contributor
timestamp: July 06, 2018, 12:27:36 pm
content: Quote from: T3sl4co1l on July 06, 2018, 12:00:45 pmI am at work will be after the weekend probably. But I will try to explain below in words.QuoteBefore these copper cables will be attached the situation is:Metal box 1 : grounded through earth (mains) but 2,5mm2 cable to mains junction box or how you call that.Metal box 2: grounded through earth (mains) but 2,5mm2 cable to mains junction box.CNC machine not grounded at all.CNC stand not grounded at all.The cables from box1 and 2 are shielded but the shield is ONLY connected on the connector on the box side, NOT on the cnc machine side. This is to make sure no equalisation currents are running but I still want to shield the environment from the noisy vdf and motor cables. This is discutable since I know that one side shielding will not protect from some fields so my other option is to run an extra earth cable in the cable (so 4 pole instead of 3 pole) and hook the earth cable to the shield at the motor or spindle connector, but anyway the result is the same there is no ground-loop current running from the box to the cnc machine, they are seperated.Now the motors and spindle are mounted on the cnc machine so their body is hard connected to the cnc machine chassis, so the chassis should be grounded, for safety but also for emc I guess (correct me if I am wrong since I am not an EMC expert at all).So to get an equivalent potential on the boxes and the cnc machine in respect to earth/ground the CNC machines and boxes have to be connected together in a star topology.The Star point is the ControlBox earth bond point, that will be the point the large copper cables will go to the stand and the chassis of the cnc machine and vfd box.So that is what these cables are for to simulate as if they all three were bolted together on a metal chassis.Hope that is a bit more clear? If I make wrong assumptions or design error I would like to know that ofcourse.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 06, 2018, 01:05:55 pm
content: So there are two mains circuits, from the main junction panel, one to each box? Are these metallic conduit? (If the line filters are doing their job, this shouldn't matter.)You didn't list more connections, how do "Metal box 1" and "Metal box 2" connect to "CNC machine" and "CNC stand"?Is "CNC machine" just sitting on top of "CNC stand", as the names suggest? Is the stand incidental, or is there anything electrical on it, too?You also later mention a ControlBox but didn't say how it connects.It sounds like you're being very paranoid about ground loops, as in safety ground. I don't know of any problem with bonding already-grounded appliances together (but, someone better versed in CE code, do chime in?). It doesn't sound like you're measuring tiny, low-frequency signals between boxes, so ground loop (as might apply to audio systems) is a non-issue.The reason I'm asking very precisely is, whenever I see "star ground" I aminstantlysuspicious. Star grounding isalmost exclusivelyapplied badly. Like slotted ground planes, it's a massive pitfall for newbies. Yes, it's a thing; and the designer should know about it. The technician even, say when it comes to pro audio systems, or setting up lab or test equipment. It is a possible option, another tool in the toolbox. But as with all tools, one must be keenly aware of its conditions, traps and downsides. And these gotchas are far more numerous, for star grounds and slotted grounds and such, than the benefits are. And because there are so many gotchas, it's very likely one or more will always be missed.It's an electronic design equivalent ofRoko's Basilisk. It's literally a kind of story that is better left untold, so people don't try to use it just because they, I don't know, think it's neat?So that's where I'm coming from, and just want to sanity-check here.By far, the biggest sin people commit, regarding star grounding, is the same problem as with slotted grounds: running connections between sides, rather than following the ground path. Crossing traces over a slot, takes exactly the current you meant to avoid, and puts it into the traces (or vice versa); connecting a cable between two boxes, that are star grounded separately, creates a loop that's altogether worse than, say, routing the ground with the cable itself (or, better yet, running the cable and ground together through a conduit).So, at this point, it seems like you'd most benefit from using metallic conduit (flexible if needed) between the various boxes and machines, so you can get the drivers' noise currents back from the motors, inside a conduit, rather than with a huge loop around all kinds of metalwork, that will radiate. Or if conduit is unacceptable, filtering the offending sources (but, that's probably even less practical -- you can't simply hang a line filter on a VFD output, unfortunately).Tim

author: X
author_rank: Regular Contributor
timestamp: July 07, 2018, 10:59:18 pm
content: With thick cables, I score the insulation with the strippers, then twist the insulationwhileI am removing it. No waste, and the twist looks very clean, but you may need to practice to avoid broken strands.EDIT:I should mention, it works well even for bog-standard 14-strand security cable. This method tends to be difficult with very thin cable (eg. found in chinese USB cords).

author: Docara
author_rank: Regular Contributor
timestamp: July 09, 2018, 04:11:47 pm
content: NO NO NOYou're not working on yuor car!On cables the size you're dealing with - you should NEVER twist cables together or put two cables in one connector - that's it! Its against the wiring regulations.When crimping is done properly it forms a better joint (than even soldering) with much lower volt drop across the joint. When crimping is donecorrectlyit fuses (practically welds) the copper to the lug without stressing the cores or causing the joint to over heat in use.The lug size is closely matched to the cable CSA witch should be matched to the (hydraulic) crimper you use. The top companies match their lugs to crimper. If you are using tri-rated or highly multi-stranded cable like you are, then you should also opt for a heavy duty lug which helps to maintain to longevity of the joint.Now taking the twisting point further.By twisting the cores inevitably you will have cores crossed over each other - probably multiple cores in practice. This causes local high pressure stress points when crimped together with a cable which is thicker than the lug was designed for. The crossing of cores will result in some cores breaking when crimped causing drop in current carrying capacity of the joint. Having a lug over compressed because the cable is thicker than it was designed for can also be a point of failure because the copper can be compressed enough to crack or cores break again causing a drop in current carrying capacity of the joint. The joint will probably overheat in operation as a consequence of the joint becoming slightly looser in operation.'Doubling up' cables.Again as mentioned above lugs are designed for cables od a certain Cross Sectional Area. By forcing cables into a lug which it (they ) are not designed for is increadable bad practice and potentially dangerous for the reason stated above. I am an Electrical Test an Inpection electrician based in the UK and I would fail a joint crimped like this.The proper way to terminate your cables is to individually crimp them with the correct size lugs and connect them together with a Bus Bar or similar.

author: Kjelt
author_rank: Super Contributor
timestamp: July 09, 2018, 06:18:49 pm
content: Well noted and you're right.If the cables were used for high amperage I would certainly do so, however the cable is for ground potential equivalence, highest current would be perhaps a few mA.

author: senso
author_rank: Frequent Contributor
timestamp: July 09, 2018, 08:31:44 pm
content: If its for grounding and you expect a couple mA, why dont you just use 4mm^2 cable with m8 eyelets and crimp it properly and just run a wire from the cnc base to one of the Rital enclosures?

author: Docara
author_rank: Regular Contributor
timestamp: July 09, 2018, 09:25:11 pm
content: What does high amperage have to do with what your doing. A crimp joint is a crimp joint.What is you application / installation - metal work in a field or machinery?

author: Kjelt
author_rank: Super Contributor
timestamp: July 10, 2018, 06:25:23 am
content: That has all been answered in posts above, it is about mutual grounding and EMC, bringing the same grounding to three metal enclosures and chassis together that are connected to a cnc machine.When I have time I will open a new topic with again more details since the questions and challenges from T3sl4co1l are quite relevant.

author: BradC
author_rank: Super Contributor
timestamp: July 16, 2018, 04:14:04 am
content: Quote from: Ian.M on July 04, 2018, 08:03:25 pmJust a loud vote of thanks for this concept.This morning I had to re-do an improperly crimped connection (a mangled 50mm2lug on a 35mm2cable) and I was having a pig of a time getting the cable into a correctly sized lug. It's one of those super flexible cables with a gazillion strands and it's a nightmare to work with. I bound it tightly with some 0.25mm diameter (30AWG) tinned copper wire and it slid right in. I've fought these connections for years, so have a virtual beer on me!On that note, I can't believe the amount of times I've seen way oversized crimps on cable that is obviously too small. Maybe if everyone knew this trick they'd use the right sized connectors.