That's possible--the ground traces tend to be nice and big.
The Ethernet port is supposed to be isolated to 1500V. USB has no such isolation requirements.
Incidentally, it was the fear of something like this happening that made me put that nice screened (shielded) Ethernet cable my old cable modem came with in the trash and use a non-screened one.
And perhaps the Ethernet port WAS used and IS a screened Ethernet cable. I have this exact modem, let me go take a measurement..
Well, this modem does not have an Ethernet port that is screened (has the metal piece on it which makes contact with the metal shield on the RJ45 plug). The old one I had did.
However, the USB port's ground is connected directly to the incoming coax cable's ground. I checked it with a multimeter.
Conclusion? Using the USB port on this cable modem is a DUMB idea. (Especially if the condition of the ground block connection on your cable drop is questionable, like most of them).
[This message has been edited by brianl703 (edited 12-18-2006).]
