On Jun 2, 1:46*pm, Rich Webb wrote:
On Sun, 02 Jun 2013 09:15:06 -0600, bud--
wrote:





On 6/2/2013 7:39 AM, Jamie wrote:
Rich Webb wrote:

On Sun, 2 Jun 2013 02:05:29 -0400, "Humbled Survivor"
wrote:

Can I ground out my outdoor FM antenna from the pole?

Does the negative of the coaxial cable have to be grounded?

Which method is best for preventing lightening strikes?

Ref: NEC 810.15, 810.20, 810.21

Both the antenna mast and the signal lead-in (via a listed antenna
discharge unit) should be grounded IAW the above sections.

But the provisions of the NEC are not to protect from direct lightning
strikes to an antenna - much more elaborate protection is required. They
can provide protection from other surge sources, like near strikes.

For best protection the ground from antenna line entry protectors must
connect with a short wire to the power earthing system. You want to
minimize the voltage between power and antenna wires.

Roger all of the above.

Re-reading the OP's question, he may have been asking if he could
ground the mast to the premise ground and bond the signal downlead
discharge gizmo to the mast's ground wire.

* * \ * */
* * *\ */---.
* * * || * *|
* * m || * *| *R
* * a || * *| *F
* * s || * *|
* * t || * *|
* * * || * *|
* * ,-++---[ ] *discharge unit
* *| *|| * *|
* *| * * * * `---------RF--
* *|
* *| grounding wire
__|+___
* || premise ground rod
* ||- Hide quoted text -

- Show quoted text -

If you get a 100,000 ampere lightning strike directly to anything
other than a metal building, the V=IR (voltage = current x resistance)
drop is going to raise the voltage of everything tied together many
many volts. All you can do is try to keep everything at the same
(elevated) voltage to avoid killing people/animals. This is done by
tying everything to the same local internal "ground". By having a low
impedance to earth ground using grounding rods and water pipes, you
try to minimize the difference between the local ground and the earth
ground. The current from a lightning strike will induce many
thousands of volts in any conductor a few feet long within 1000 feet
of the actual lightning strike. I have seen an arc form from a tv
lead-in wire to a ground when lightning hit 2000 feet away. The arc
jumped a 1" air gap, so the arc voltage was well over 1000 volts. A
protection device on the lead-in wire would probably have kept that
voltage under 100 volts. So grounding the antenna mast helps, but a
protection device on the lead-in is adding suspenders to a very weak
belt.