Joseph Mack wrote:
Greg Brown wrote:Having spent several years as a cabling grunt, I can safely say that almost all the Cat-V cable I've seen pulled, even as far back as 7-8 years ago, was solid core. For permanently installed cable you don't really have the flexibility concerns to worry about at all, but there are other considerations at play. Consider that when punching down a station wire into a patch panel, the wire is slipped between two sharp edges, which essentially cut the sheathing and dig into the wire. This works quite well with solid core wire, but can have unpredictable results with multi-stranded wire. Individual strands can break off and pull away from the conductors, and you may not get a solid punch. I have used multi-stranded wire in fixed-wire installations once or twice, and not only is it simply more difficult for me to work with it, due to it's more flexible nature at the individual-strand level, but I personally don't think it will make as good a connection. I have seen no statistics that back up or contradict my assessment, just drawing logical conclusions from having seen hundreds of buildings wired.
Home Depot now carries plenum rated Cat5 at ~$160.00 per 1000 foot
spool.
The default cat 5 cable now seems to be single stranded, but when it first came out, the default was multistranded. The conventional wisdom
from my electronics days is that the single stranded conductors can't
be flexed a whole lot (eg used for cables that are plugged and unplugged)
as they crack at the flex point giving you an intermittant connection
that will drive you nuts trying to debug.
I guess single stranded is OK for plenum cable that terminates in panels, but for cables that are connected to computers that get plugged and unplugged you should use the multistranded conductor cable.
Joe
Now consider a patch cord - where flexibility is certainly a concern. Discounting those cables that were blatantly abused, I don't think I've ever seen a cable where the problem was in the "middle" of the cable. Cabling problems can, in my assessment, almost always be attributed to the crimp at the ends; and it's usually a fault in a hand-crimped cable. So personally, I don't think the increased flexibility of multi-stranded cable really brings that much of an advantage. Let's consider again how the crimp of an RJ-45 connector connects with the individual cable. There are 8 individual metal contacts, which when crimped slide down and pierce the jacket of the cable. They dig into the tip of the cable for their contact. If you've any doubt that wasn't intended to punch into a solid conductor cable, see my above comments about multi-conductor cable and bad contacts. :) Either way though, the usual problem with patch cables is that the person who crimped it either a) didn't ensure that the ends were cut evenly, and each tip was flush at the end of the connector and was caught by the descending crimp, or b) the sleeve was cut too far back, and is not inside the connector and crimped down by the rear plastic triangle designed to hold it in place. If that's not in place, stress on the cable will eventually pull the ends loose, just as if (a) hadn't been completed successfully. The third and final common problem is that c) the plastic piece in the back meant to secure the jacket (described in b) broke during the original crimp, and fell away. This is common with low quality crimpers, or low quality ends - if the tolerances are not just right on both the crimper will push the plastic piece beyond breaking away just one side and having it lodge in place, still attached at one end - so much so that both ends break and the securing-piece falls entirely away. I suspect if I knew the name for that piece of plastic this would all sound much more informed, but oh well. :)
Having said all that, this is why I believe it's almost always worth the few bucks to buy pre-made and pre-tested patch cables. They're almost always better than you can do by hand, even with lots of practice. To boot, they're usually cheaper when you account for the time spent making patch cables by hand. Check into pricing at a real cable supply house, some where like Graybar or any of the various online suppliers, sub $1 prices for most lengths are not uncommon. Now don't go throwing away your crimp tool and ends - putting ends on cables is still required in some circumstances. Consider a T-1 run from one side of the building to the other -- gotta put ends on it to plug it into the remote box, because the decision maker is usually too cheap to justify putting in conduit and a box, labeling it, and then using a patch cord from the box to the device...
If anyone else has any insights or disagreements, I'd be quite interested to hear. I am not an authoritative source on cabling by any means, I've just observed the common industry practices for the better part of a decade and am kind of a stickler when it comes to proper cabling.
Aaron S. Joyner -- TriLUG mailing list : http://www.trilug.org/mailman/listinfo/trilug TriLUG Organizational FAQ : http://trilug.org/faq/ TriLUG Member Services FAQ : http://members.trilug.org/services_faq/ TriLUG PGP Keyring : http://trilug.org/~chrish/trilug.asc
