I'm about to run Ethernet cable, some new runs and perhaps replacing
existing old cable, which is Cat 5 CM (not 5E!) that was free to good
home over 20 years ago (pulls from a commercial data center that decided
they needed CMP). There will be some outdoor (on the house, not
planning interbuilding) and some attic. The root switch is AC powered,
and remote switches, APs, and a few other things are POE-powered. Most
things are Ubiquiti UniFi.
Before I get to RFI concerns, for outdoors and highly likely attic the
cable needs to be outdoor rated (UV and water), and code says anything
inside needs to be rated CMX and <= 0.25", or else CM or better. (CMX
is a fire rating, and does not mean outdoors, but typically CMX and
outdoor go together. However some outdoor cable is not even CMX rated.)
If other than a 1/2-unit dwelling, code would require CMP in plenums,
CMR for vertical runs, and >= CM for the rest (except for outdoor CMX
coming in < 50'), and I'm inclined to follow that as a good idea though
not required. (I wonder if NFPA will change the code with houses being
much more wired; it seems the "CMX ok" is perhaps about "but you don't
have much of it".)
Generally the world recommends shielded outdoors, with that being
omittable if all runs are along the building and perhaps not so long
outside. This is about lightning (distant more than direct)) and static
buildup, as I understand it.
With unshielded indoors, I don't really expect a ground reference at the
remote switches etc. With everything shielded, all the networking
equipment is basically star tied back to the root switch. So it doesn't
make a lot of sense to me to run shielded outdoors and unshielded
indoors, unless I have ground connections at each switch connected to a
cable that goes out. Most of my switches are intended to be POE powered
and do connected the shields of shielded cables.
So it seems reasonable approaches would be:
everything shielded
everything unshielded not worrying about short outdoor runs
Before posting I reviewed RFI-HAM :-) and my summary of that is that one
needs choking impedance for common-mode, and that WiFI has less
interfence. There wasn't really any support for shielded Ethernet cable
being better. But also no support for it being worse.
It makes intutive sense that shielded cable would be less trouble, but
there is the point that all the signals are differential on high-quality
twisted pair, arguing that it won't matter much. But, having a DC
ground even if not low impedance at RF is appealing.
It seems shielded costs a bit more. A lifetime buy of 1000' each of CMP
and outdoor 5e is $123 more, and then connectors are a bit more. It's a
bit bulkier, and bit more work to terminate. It doesn't seem to have
any major issues.
I would like to hear
- opinions about the value of shielded vs unshielded Ethernet
(assuming chokes held constant).
- opinions if sihelded outdoor to non-grounded switch with unshielded
back to grounded switch makes sense
- experience of anyone who has faced this choice especially their
rationale before and their hindsight opinion later
- experience of anyone who has done an unshielded to shielded
conversion and their hindsight opinion.
73 de n1dam
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