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

Bill Whitlock engineer_bill at verizon.net
Mon Nov 4 17:08:08 EST 2019


Cory,
With all due respect, if you're proposing that a driven ground rod is a *substitute* for the green wire (or conduit in very old buildings), this expert says you are DEAD WRONG!!  The safety provided by the green wire is not due to its earth connection.  Safety comes from providing a very low-impedance path back to the neutral at the main panel, so that fault currents (which range from 150 to 1,000A) will quickly trip the circuit's breaker. The essential connection for the green wire is to neutral, NOT to earth ground. In my seminars I have a slide that schematically shows this "clean ground rod" tied to outlet 3rd prongs *instead" of "that noisy green wire*.  If an equipment fault occurs, the chassis of the faulty equipment stays at or near 120 volts and the little current that flows between the new "clean" ground rod and the ground rod at the building power entrance (the only path now left to the fault current) is very small - not nearly enough to trip the circuit breaker - so the faulty equipment remains a lethal shock hazard!

I sat in on a CEDIA seminar by an alleged expert (owner of a company that was hyping its power conditioning gear) who proposed exactly this idea.  He had the nerve to argue with me!  Fortunately for me, there was a master electrician in the audience, who cited Code and explained why doing so is potentially lethal. If someone gets a bad shock or is electrocuted, you will be hit with a lawsuit that will wipe out your company ... yes, it's happened. The judge won't give a rat's ass how the hum went away - fact is, your modification will be the cause of injury or death. The guy who presented this life-threatening information was banned from CEDIA when I reminded them of their legal liability.  This seems to be one of those "zombie ideas" that just won't die ... but this one is particularly dangerous!  All that being said, Code does allow for additional earth grounding, but the path provided by the green wire must never be interrupted (and must stay inside the same conduit as the line and neutral conductors of the circuit it protects - for reasons of inductance and path impedance under fault conditions.

Bill Whitlock
Whitlock Consulting
Ventura, CA
AES Life Fellow, IEEE Life Senior, and UL Pro Audio Advisory Panel member



-----Original Message-----
From: Corey Bailey Audio Engineering <proaudio at baileyzone.net>
To: proaudio <proaudio at bach.pgm.com>
Sent: Mon, Nov 4, 2019 4:10 pm
Subject: Re: [ProAudio] AES on the west coast, was Re: Ampex/ProAudio List Dinner

 Jim Brown, Bill Whitlock & David Josephson: All great advice, For equipment that I want to be truly ground isolated, I use a driven stake (Grounding Rod) and avoid AC ground if at all possible (local electrical codes be damned!). Then, follow the advice of someone who's knowledgeable on the subject of proper grounding. (Like, any of the three mentioned above.) Cheers! Corey
  Corey Bailey Audio Engineering
www.baileyzone.net On 11/4/2019 10:18 AM, Jim Brown wrote:
  
On 11/3/2019 7:38 PM, David Josephson wrote: 
 
For instance as Jim Brown says, every conductor is an antenna. 
 
 
 My favorite quote on this topic is from Henry Ott, who in his lectures spoke of the hidden schematic lurking behind the ground symbol. Since my retirement, I've been devoting my energies to ham radio, teaching fundamentals to folks with a wide variety of technical backgrounds. No surprise, the Pin One Problem is a hot topic -- Neil Muncy repeatedly told me that it was the primary mechanism behind RFI, and work for a paper that David and I co-authored in 2003 proved it. Fast forward to today, Pin One in CATV and DSL systems is the cause of EGRESS of RF noise that pollutes the radio spectrum. 
 
 I do, however, strongly object to the phrase "ground loop," instead using Bill's excellent model showing the mechanism as a difference in potential chassis-to-chassis between interconnected equipment (or chassis to ground) t as the cause of shield current, whether that difference is created by IR drops in green wires or antenna action. The reason I so strongly object is the that solution, especially in small very local systems, is so often proper bonding, which visually creates a loop with signal conductor shields. I'm thinking here of a home entertainment system or a ham station. I use a drawing of Bill's model in my talks and on-sine tutorials. 
 
 I stopped teaching at trade shows several years ago because I was unwilling to participate in one held in Florida, in protest of the acquittal of that vigilante murder and the law that allowed it. 
 
 As to our conventions -- my interest has always been in the papers and workshops, and hanging out with colleagues. In retirement, I can no longer justify the cost of a convention that requires a hotel stay in an expensive city. 
 
 Henry Ott also did a great breakdown on the inductance of a wire as part of a loop. 
 
 Jim Brown 
 
 
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