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
|