[TriLUG] OT: Home Depot and Cat 5

[Aaron S. Joyner]

Joseph Mack wrote:

>Greg Brown wrote:
>  
>
>>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
>  
>
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.

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