I mistakenly cut a flat CAT7 cable I just purchased.

Can I just open the strands on the two ends attach them to each other? Like twist them together and put tape over it? Would that affect performance?

Looks like there are eight little wires in there. I know a lot of delicate splicing and then I have to make sure each wire is separately taped.

Or would it be better to forget about the part that was cut off and buy a connector, like this?

I have more than enough cable so losing length I don't mind. If I take this route, do I have to buy a crimp tool too.

I can't believe how much trouble I created for myself by this mistake. I can't just replace the cable because it has already been pulled through an underground PVC pipe.

I rather not to spend more money if just twisting the strands together would do the job. Cable would be hidden away so no chance of later getting pulled and wires untwisting.

enter image description here

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    Have you considered using the current cable as a draw string for a new length? (Also next time make sure you have a drawstring in your conduit!) – davidgo Jun 9 at 10:40
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    I think I'm going to listen to you guys and use the current cable as a pull rope for a new cable. I didn't consider it before because I am worried it somehow gets stuck somewhere. It's a 1" conduit but when I was pulling it through when I was laying the conduit, sometimes it felt like it was going to tear. But it seems pulling through a new cable beats all the work associated with repairing the cable. – polaatx Jun 9 at 15:57
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    Also, I doubt that cable qualifies as CAT-7. For starters, the conductors look way way too thin. They look like maybe awg-33 (Ø0.17mm), but I don't think anything finer than awg-24 (Ø0.51mm) can qualify. That's almost 10 times too little cross-section. Also, as far as I know, CAT-7 requires an overall shield, and requires pairs to be twisted around each other. Finally, I have my doubts about the connector. If you expect actual CAT-7 performance, you might be disappointed. – marcelm Jun 9 at 18:11
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    @polaatx - If you have enough reserve cable length, pulling 3' more cable through and adding a connector is the path of least resistance (just make sure it's a connector designed for the flat cable you have, and order a handful of extra connectors to practice with). Worst-case scenario, you can always to back to the "fish a new cable" option. – bta Jun 10 at 21:52
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    @polaatx consider running two cables instead of just one. A 305 metre (1000 foot) box of wire would be ample, and you then fit jacks on the ends. However you need to consider power as well - if the two buildings are on different phases then there can be a differential and you get an AC voltage on your copper ethernet. A Fibre optic run may be a better solution for you here. – Criggie Jun 11 at 1:48

Can I just open the strands on the two ends attach them to each other?

Not if you want Cat7 performance. If you are intending to use this for 10Gbps Ethernet you need to use proper methods for joining and terminating the shielded twisted pairs.

If you are using this only for 12V DC between doorbell and pushbutton, you'll be ok.

Or would it be better to forget about the part that was cut off and buy a connector, like this?

yes and no.

That connector is not suitable for flat-cable, you need a special connector for flat Cat7 cable. To be sure of doing it right you'll need specialized tools too. You probably need to practise on spare cable until you can get it right every time.

You can then use an inline coupler rated for Cat7 (if such things exist) but you should really also use cable performance testing tools across the whole run to check that the joined cables still meet Cat7 standards.

You could just wing it, but the downside is you might get disappointingly poor performance and years of troubles that are a constant annoyance and faults whose cause is hard to trace.

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    This is the best kind of "definitely maybe" answer this kind of question will get. Just "twisting together" is unlikely to make a particularly good or reliable connection and is just going to hurt performance, especially if this is a cable expected to link together two devices with high bandwidth requirements. It might work, but when you abandon the job/home/wiring the next person who has to deal with it will be cursing you. – Mokubai Jun 9 at 9:13
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    I did something like this to a Cat-6 cable once. Do not simply twist the strands together. Solder them delicately. Keep the soldered parts as short as possible. Do not use tape for insulation, use heat-shrink tubing. Provided you have the skill, the materials are cheap. You probably end up with a 1 GBps connection, but properly soldered, even PoE will be no issue. – Hermann Jun 9 at 22:14
  • If you have them, there are some nice flat crimp-on connectors (Dolphin is the main brand that sells them but you can buy them unbranded) that may do the trick better than solder. I love them when I need to splice Cat5 back together. The catch here is they're probably not rated for true Cat7 use – Machavity Jun 10 at 16:20
  • @Machavity Forgive my ignorance: I would use the White B-Connector Wire Splices you linked to for attaching EACH of the eight little thin wires insider the cable, correct? So in total I would use eight wire splices? You're saying doing this is same as soldering that Hermann prescribes? I am total newbie. – polaatx Jun 10 at 17:29
  • Correct. If you merely want to reconnect the wires, you strip them, put them in the splice and crimp. You would need one per wire, or 8 total. – Machavity Jun 10 at 17:31

I absolutely don't believe that what you bought would test to Cat7 requirements even when brand new. Cat7 is a proprietary standard, and as such is not terminated normally in RJ45 connectors, but in GG45 - backwards compatible with RJ45 receptacles, but looks more expensive (and is!). And you won't buy the tools to terminate it in a home improvement store. And you won't buy the cable flat. There's not much flat Cat7 cable sold by reputable professional cable vendors, and its uses are specific: multimedia in living spaces without running in the wall. It's not used to be pulled in any sort of conduit. It goes from a jack somewhere, then gets concealed (e.g. under carpet outside of walkable areas), and ends up in something in someone's living room, usually.

You had been had. Sorry to bring such bad news. What you wanted to buy (but didn't know) was Cat8 cable.

There's no splitting Cat7 nor Cat8 cables, pretty much. It's not possible to do in any sort of field conditions while still retaining full Cat7 or Cat8 performance. If done well it could perhaps "work" in that the endpoints were able to negotiate a 10G connection, but it'd be very, very iffy.

I would have had trouble doing even it in a well equipped electronics lab: in addition to a network analyzer (or a comparable instrument), I'd need an expensive test fixture allowing to connect each pair separately to the analyzer ($1k+ just for the fixture). I'd be laser welding the ends of the wire together under a stereo microscope, in a suitable fixture. No soldering anything, and the splice would be staggered, so that one pair each would be spliced every inch or two. That's to minimize crosstalk. Cat7 and Cat8 have quite stringent internal and external (alien) crosstalk specs. I've done it before without any testing other than the network equipment itself, and it worked fine, but it was hard to tell how close I got to the original performance. And it was done just to show that it could be done - beware of bets made over beer. I'd never use it for anything else.

So what you will do if you actually want 10G or 40G performance is as follows: use the old cable to pull a replacement through the same conduit, and forget about the whole Cat7 brouhaha. It's proprietary and you don't need it. And if it's cheap, someone is possibly lying to you.

If you're connecting within the building, then use either Cat8 cables if you truly need 10G-40G performance, or use Cat6e. I have had lots success with Monoprice Entergrade Cat8 patch cables. 50ft white will currently cost you about $50. There are other vendors, but you must inquire on homelab or similar forums about who is reputable. A random Amazon seller - not so much. If they are not in business of actually selling networking cable (and typically other networking gear) - forget about it.

If the underground connection is between buildings, then you're asking for trouble by using copper cable. And the trouble will come when you get a lightning strike close enough. You'll be pulling a replacement cable as well as replacing some gear. Not good.

Thus, for inter-building connections, you'll use your cut cable to pull one or two pairs of half-duplex LC-terminated single mode fiber patch cords (2 or 4 cords in total). Those are relatively cheap to interface with, but you're looking at about $300 worth of fiber and transceivers to get one 40G link up, with an extra two fibers dark as backup or future expansion. I'm assuming you have the network cards that support 40G SFP+ transceivers. If you want to be switching at those speeds - well, that gets expensive...

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    I suspect that sellers like this one use "Cat7" as a generic shorthand for "Of course this cable is way better than the lowly Cat6 everyone else uses, because obviously 7 is more than 6, so you totally have to buy this and it'll make your internet super fast!". – TooTea Jun 10 at 13:38
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    @polaatx Absolutely do not use copper connections between buildings. You need fiber. And it won't get stuck or torn if you do it properly. The fiber patch cord connectors will need to be staggered along your "Cat7" cable so that there's 4-5 inches between each connector along the length. Allow at least 12" from the last connector to the cut end of cable. Wrap everything tightly in thin masking tape - the yellow "delicate surfaces" Frogtape works well.Make sure you keep that tape stretched so it doesn't create a bundle that's too thick. – Unslander Monica Jun 10 at 18:12
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    "Cat7 is a proprietary standard" – Could you explain why you are singling out Cat7 here, since it is standardized in the same document as Cat5, Cat6, Cat6a, Cat7a, Cat8.1, and Cat8.2. So, if Cat7 is a proprietary standard, then so are Cat5, Cat6, Cat6a, Cat7a, Cat8.1, and Cat8.2. And secondly, if you consider an ISO standard proprietary, what would you consider not proprietary? – Jörg W Mittag Jun 11 at 7:32
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    @TooTea: So, because it's "only" a world-wide standard specified by ISO, but not a US standard standardized by TIA, that makes it "proprietary"? That is a strange worldview. Here in Germany, we generally consider ASCII, ANSI, NIST, FIPS, etc. standards "standards" even though they are only valid in the US. And most people would consider ECMAScript standard even though it is only standardized by the European Computer Manufacturers Association. – Jörg W Mittag Jun 11 at 11:05
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    @polaatx I just want to note that since you only need half a Gbit, 1G fiber-to-copper media converters (Google that) will be significantly cheaper than the USD 300 that this answer quotes for a 40G setup. If you have a switch that takes fiber modules use that, ontherwise there are dedicated small boxes. – Law29 Jun 11 at 17:03

Re-pulling suggestion:

I suggest you use this cable to pull some strong light cord (e.g. paracord). The join can be made really solid - knot the paracord tight around the cable 25-20 cm (6-8" from the end), and tie off the loose end. Also knot the cable round the paracord. The end result will be not quite a fisherman's knot as the cable is too stiff; a sheet bend would work but leaves the end of the cord sticking out too much. You can also use use fairly small cable (zip) ties pulled tight.

Wrap over the join with electrical tape, starting at trailing end and finishing at the leading end so the edges can't snag. Pull the tape quite tight except for the last 2 turns.

Then use the paracord to pull the new cable (joined in the same way), and another length of paracord so you've got a pull rope for the future. I used to pull bundles of cables this way in a previous job, up to 3xCAT5 + 4x terminated fibres down a 20--25 mm (3/4--1") conduit. The longest was 100 m (300') and that wasn't straight.

If it does break, don't panic. You can get a string down a conduit with access only at the ends, using materials you have or can buy cheaply (vacuum cleaner, kite string, paracord, duct tape).

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  • I can add more info on the vacuum-pulling we used to do if you need it – Chris H Jun 10 at 19:39

To elaborate on the other answers, the difference between Ethernet grades of cable is shielding.

  • Cat5e is merely twisted pairs
  • Cat6 adds a plastic separator between pairs
  • Cat6a depends on the type, but most often comes with foil in the other sheath, or with foil wrapping the twisted pairs
  • Cat7 typically adds an extra layer of shielding around the cable (two layers vs 6a's one). It also uses very different connectors from RJ45 (as another answer noted)

The wire in your photo has parallel untwisted wires with a simple nylon sheath. It might have foil wrapping around the wires (hard to make out). So it might make it more like 6a than 7. Either way, assuming you want to maintain the shielding, I would put a Cat7 keystone on both ends and buy a 1ft or 3ft Cat 7 to go between. Crossing your fingers and trying to put RJ45 in is asking for trouble. A Cat7 keystone is rated to maintain the shielding. Just be aware you might need special tools to install one

If you don't care about the shielding, just go to your local hardware store and buy some Cat6 ends and do the same thing, but with mere Cat6.

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  • In addition to shielding, it's also the manufacturing tolerances that are tighter for higher-grade cables in order to ensure the required RF propagation characteristics. – TooTea Jun 11 at 11:12
  • Sorry, but according to the product description in the Amazon link, that IS shielded twisted pair. You just can't see it in the photo OP provided. You can see it in the Amazon descriptive photos. – Law29 Jun 11 at 16:23

To answer your implied question of "is this fixable" then yes it can be bodged together with twisting, wire nuts, scotch locks, solder, etc and will "work"

The problem comes when you expect this link to perform at its rated throughput and maintain a higher link speed.

I've seen these cables work perfectly at 100 Mbit but get repeated transmission errors at gigabit. Own work - no... my own photo of someone else's shitty work some electrician used two short pieces of 4 core bell wire to pass through two separate-adjacent holes in a wooden beam

Point is - even if you did fix your cable, and it works at your current speeds, it could easily fail when new kit is attached to the ends.

Answer Replace your broken cable with new ones so there's spares. Run draw wires too for next time/future upgrades. Consider how it got cut and avoid doing that again.

Since this is buried, its also a potential fire risk if some future user puts POE across the link too. And its a trap when pulling other cables through in the future.

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  • Hi there, great advice. What is a POE? – polaatx Jun 11 at 4:50
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    PoE is Power over Ethernet – methods to carry 12–48V DC over the same Ethernet data cable (similar to "Phantom power" in audio). Often used to power up security cameras and Wi-Fi access points. – user1686 Jun 11 at 6:19
  • Correct - POE also means there is additional current on the wire. Not a lot compared to a mains lead, but joints can cause heat as the current levels increase. To be avoided, specially when some POE links may be up to 60 watts, though ~15 is a more common maximum. – Criggie Jun 11 at 14:18

Using the tips I got on Superuser and to avoid pulling through a new cable through conduit, I spliced the damaged Cat7 cable together using White B-Connector Wire Splices for Low Voltage (100 Pack) suggested by @Machavity. Took about 20 minutes of heavy concentration. I can't be happier. I am not seeing any reduction in throughput. I am getting 200 mbps with this repaired cable and a new one. Of course, there could be drop in transmission speed if I was using this cable for very fast connections. I can't measure that because I don't have the equipment. Thank you so much for the help. Superuser forums have saved my behind many times.enter image description here

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