[TenTec] Earth those feeders

Jim Brown k9yc at audiosystemsgroup.com
Tue Sep 13 13:57:23 PDT 2011


On 9/13/2011 8:39 AM, art davis wrote:
> Does this mean that I am in violation of the NEC if I disconnect my coax and throw it out the window without grounding it?

No, but it makes you look stupid, because you are sticking a lightning 
attractor high up in the air, but failing to provide a discharge path 
for it.  When you do that, lightning will build up a charge on that 
attractor, and  find its own discharge path that may or may not be a 
path you would have chosen.  Those who believe that simply disconnecting 
antennas is a good thing should read what W8JI, a retired broadcast 
engineer, has to say on the topic. Google to find his website, which I 
think is w8ji.com

> How about ladder line where neither wire is a "ground"? . I don't see anywhere in the post where it is being recommended that the safety ground (green wire) be disconnected (the word "feeder" in the original post referring to antenna feeders, not power feeders). I gotta believe he means to disconnect/isolate the antenna feeds from the radio to break any ground loops that may exist by having both the chassis grounded and the coax grounded in different places.

The entire concept of a so called "ground loop" is fallacious.  As a 
young engineer, I could never draw an electrical circuit that explained 
the idea, and as a mature engineer specializing in audio, EMC, and RFI, 
I now know that it is completely wrong-headed.  The hum and buzz that 
occurs with many things interconnected using unbalanced wiring is caused 
by LEAKAGE CURRENTS from the AC power line. My tutorial on interfacing 
ham gear to computers discusses this in great detail.

http://audiosystemsgroup.com/HamInterfacing.pdf

> Also, keep in mind that the NEC is written by the insurance companies.

No, it has NOTHING to do with insurance companies.  You are confusing 
NEC with UL (Underwriters Laboratories), an independent testing 
laboratory that tests products of all sorts, primarily for fire safety 
and shock hazards.  The UL Standards by which testing is done are 
established by consortiums from the industries for each product 
classification.

NEC is VERY different. It is a model Electrical Building Code jointly 
written and agreed upon by top engineers from many disciplines affected 
by the code.  By itself, it has no force of law. But when it is adopted 
by local building departments that are part of local governments, it 
DOES carry the force of law.  I know a few of the engineers who have 
contributed at one time or another.  The NEC is revised every three 
years to address changes and additions needed to accommodate new 
equipment and technologies. The changes are always "nibbles around the 
edges," not major changes to how things are done.

About ten years ago, I was commissioned to write a tutorial on Power and 
Grounding for Audio and Video systems.  It includes many references to 
NEC, and to other building codes around the world. It's on my website.   
http://audiosystemsgroup.com/publish.htm

73, Jim Brown K9YC



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