USB is using 3.3V for data transmission and 5V on a wire for power. On a RJ45 plug you can find all voltages from 2.2V to 120V, depending on where you plug that cable to (ethernet, PoE, phone analog or ISDN...)
Generally you must not connect USB to any network other than USB via mere wires, no matter what plugs are at each end of the cable. There are devices that have electronics inside, to adapt e.g from USB to ethernet. Usually you can tell they have electronics by the fact there's some sort of case - not always though.
My warning was about mere cables without any electronics that simply have USB at one end and RJ45 at the other end, and so directly electrically connect USB to any non-USB network or outlet.
I.E. things like that one MUST NOT be used to connect N900 to anything else than a USB port: http://www.mercateo.com/p/560-66860/...apter_Kit.html


background: http://forums.macnn.com/89/macnn-lou...-runs-through/


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