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

Bill Whitlock engineer_bill at verizon.net
Tue Nov 5 11:59:09 EST 2019


Jim,
I'm sure it was Neil who coined the phrase "sump theory of grounding" to mean that currents, especially noisy ones, flow into soil and simply disappear forever.
Regarding earth grounding of lightning protection, I don't fully understand Code in this regard. Yes, lightning strikes themselves need a path to earth - since the strike is a discharge of huge capacitance between clouds and earth soil.  But the most common equipment damage comes from voltages magnetically induced into terrestrial  conductors of all kinds. Direct strikes to premises wiring would be catastrophic. Of course, there is also a sudden drop in electric field in the vicinity and this is a problem for "floating" (un-grounded) objects. Perhaps this is the Code's concern. As mentioned earlier in this thread, it sure would be great if they could explain their reasoning!
I think of the strike itself as the (temporary) primary of a one-turn transformer.  All those metal objects on the ground (or in the air, for that matter) are secondaries. Thousands of volts can be induced into a 20-foot-long conductor, depending on whether or not it's parallel to the bolt. I've read that there are about as many cloud-to-cloud discharges as cloud-to-earth, so any orientation is vulnerable.
Bill Whitlock


-----Original Message-----
From: Jim Brown <jim at audiosystemsgroup.com>
To: proaudio <proaudio at bach.pgm.com>
Sent: Tue, Nov 5, 2019 11:32 am
Subject: Re: [ProAudio] AES on the west coast, was Re: Ampex/ProAudio List Dinner

On 11/5/2019 10:07 AM, Bob Katz wrote:
> An actual earth ground is unnecessary and frankly, useless.

Not true, Bob. Indeed, it is a critical component of lightning 
protection, which is why it is required by electrical codes. So is 
bonding. You are, however, entirely correct that an earth connection has 
to relevance to hum, buzz, or RFI. Was it Bill or Neil that so 
poetically said that earth is not a sump into which noise is poured? I 
have often used that quote in my talks and writing. It is, indeed, the 
bonding that is critical for that as well.

Jim Brown
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