Reddit mentions of Ethernet: The Definitive Guide

Read (and try to understand):
[Ethernet fundamentals!]
(http://www.amazon.com/gp/product/1565926609/ref=oh_details_o08_s00_i00?ie=UTF8&psc=1)
[Internetworking with TCP/IP!]
(http://www.amazon.com/gp/product/0131876716/ref=oh_details_o06_s00_i00?ie=UTF8&psc=1)

Both are good books and essential reading for anyone working in networks (if you want to be any good at it)...

Is this really true for Ethernet?

I understand that the two locations may have different ground potentials, but an Ethernet cable isn't electrically connected to anything. It's magnetically coupled. The copper conductors in the Cat5 cable connect only to a coil inside the NIC/Switch. There's nowhere for DC voltages to go.

Quoting Chuck Spurgeon:

There is no need to reference the signals on a 10BASE-T segment to a
common ground level shared by the equipment at both ends. By not
referencing the signals to a common ground, the 10BASE-T system is
isolated from variations in ground voltage that can occur in a
twisted-pair cabling system. This eliminates problems with ground
currents and improves the reliability of the system.

1000BASE-T and 10BASE-T have the same magnetic coupling scheme as far as I know.

...Having said that... Yeah, I'd use fiber too.