[ProAudio] AES on the west coast, was Re: Ampex/ProAudio List Dinner

[proaudio at bach.pgm.com]

On 11/6/2019 11:19 AM, Scott Dorsey wrote:
> Ethernet is a special case because UTP ethernet is completely (well, up to 1KV
> if the interface meets specs) isolated from ground on both ends.  So you can
> run UTP between systems without worry about creating spurious ground paths,
> and you have no worries about induced ground currents (as long as the voltages
> stay under 1KV).

This illustrates the falsehood of thinking about bonding and grounding 
ONLY from the perspective of noise at AF. I know of at least two 
engineers, one of them Bruce Olson, where everything that was part of 
his Ethernet network was fried by a lightning strike. This goes back to 
the days before SurgeX series mode suppressors, so he was using MOV 
suppressors, and the high potential between the equipment fried everything.

In facilities like the microwave installation Richie cited, lightning is 
also a primary issue. I've had the opportunity to study site 
documentation for an AT&T Long Lines site that David Josephson owns. 
There is a perimeter ground system for the building with multiple driven 
rods, another for the 160 ft tower with more driven rods, they are 
bonded together to power entry, and to an entry panel for hard line 
coming down the tower from multiple dishes. In the event of a strike, in 
addition to the induced currents on wiring within the building that Bill 
noted, there is also current from the tower itself, and those hard line 
coax feedlines.

There is no such thing as "signal ground" for racks -- more "sump 
theory." In addition to bonding to perimeter grounds for lightning 
protection in that microwave installation, the racks must also be bonded 
via the "green wire" from the power source. Shielding does not depend on 
an earth connection, and it DOES depend on shielding being continuous 
without breaks or openings having wavelength significant at the 
frequencies of interfering signals. Signal wiring to racks is virtually 
always coaxial for RF, and should be shielded twisted pair for analog 
audio, both with shields bonded to the shielding enclosure at the point 
of entry.

Jim Brown