Here's a tutorial that perhaps might explain some of the restrictions.
If you tied your cables to electrical conduits for any significant
length, it might still work but it could fail certification.
From a physics standpoint, what you are concerned with is
electromagnetic shielding. A grounded conduit provides nearly 100%
electrostatic shielding, but the currents in the electrical conductors
within produce a dynamic magnetic field that leaves the boundary of
the conduit and is almost impossible to shield or contain.
A few years ago, everyone was concerned about these low frequency
magnetic fields but if was difficult to prove that they caused any
They can and do interfere with communications circuits, though, and
this is why there is a specific prohibition about attatching cat5 to
I may be wrong but, I don't think that's right. That's why ethernet
uses twisted pairs of wires -- so it can reject common mode
interference. A voltage caused by a stray magnetic field would be
equally induced on both conductors of the pair and would be rejected.
You can use the center pair of wires (I'm not sure what the color code
is) for telephone. That's why a RJ45 ethernet connector uses pins
1,2,3,6. 4 and 5 were reserved by the old "Starnet" (Xerox?) standard
for telephone. You can plug an RJ11 telephone line into a RJ45 socket
wired this way to get a telephone signal. I have one jack in my
basement wired like that, but I generally run a seperate CAT3 cable for
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.