Author: "Richard W. Solomon" <w1ksz@earthlink.net>
Date: Wed, 3 Jan 2007 21:42:41 -0500
Looking for advice on what to use to protect the Tower, Antennas and Rigs from lightning strikes. I guess I need Tower Ground(s) and some kind of Coax grounding that can survive. I looked at the Poly
Most Conservative: Must operate with 5 9's availability, even after receiving multiple direct hits from positive 300kA strokes. to Least Conservative: Shrapnel from failed components doesn't fly more
Dick: Below are some nuggets of wisdom I've gathered from reading the postings on this reflector over the years. 1. You cannot protect the tower, antennas and rigs from a direct lightning strike. You
Gene, does anyone run simulations or calculations on lightning strikes. A common direct stike is 100 kA with a risetime of 8 us, correct? If so, using an inductance of 200 nH/ft, the voltage drop alo
In his well-stated list of grounding advice, Gene AD3F includes: "3. You ought to ground each coax cable shield to the tower at the top and at the bottom of the tower." I've seen this advice before,
Really? Which code? The 2005 NEC is silent on towers, per se. Art 810.15 says masts and metal structures shall be grounded in accordance with 810.21. 810.21 just has the stuff about the size of the w
Indeed they do. There's a lot of literature out there on it. Recently, there have been some interesting papers trying to quantify things other than the "direct hit".. that is, the induced voltages an
The book "grounds for lightning protection" from polyphaser has those examples and formulas in it. They tell you how to estimate how much voltage will appear in different parts of the system. You ca
The industry standard for protection device comparisons is a waveform of 8x20 microseconds. You want to see how much energy is let through with a given size strike with that wave form. If they don't
Jerry: I'm sure someone here has posited an explanation for the top and bottom ground connections of coax cable to towers. I don't recall that explanation, so I took out my copy of Polyphaser's Light
The idea is to try and keep all voltages at the same level so as not to have anything arcing as in between the cable and the tower. Further to that, grounding the coax at the very bottom of the towe
Jerry, I believe the idea is to ensure that there's not a voltage differential between the top and bottom of the coax. If there is, a charge could travel from one end to the other, damaging the coax.
Jim: I'm pretty sure I read about these new grounding requirements in the latest (2008) proposed NEC here on TowerTalk within the past six months or so. I can't just yet find that reference in the ar
The current (some say "dumbed down") Technician class question pool has a question on tower grounding. There's no reference given (I would like to find it). T0B11 (C) What is considered to be an adeq
Effective January 1, 1006; tower grounding standards in the United States are specified in ANSI/TIA-222-G-2005. Section 10.4 states: Connections between a structure and grounding electroes or connect
Think AM Broadcast -- according to IEEE data, on average, the energy in lightning has a VERY broad peak around 1 MHz (so broad that there's lots at 2-4x that frequency and 0.2X that frequency). It is
Frank: Thanks - that's the reference I had in mind. What I correctly recalled was the requirement for six electrodes (ground rods) for self-supporting towers such as my own; I hosed up on the referen
I use my tower as a quarter-wave vertical on 160. It is on a base insulator salvaged from a damaged AM broadcast tower, and I use 120 quarter-wave radials, each about 133' of #12 bare copper wire. I
They appear to assume that the guy wires on a guyed structure will be electrically connected to the tower, so that ground rods at the guy anchors will provide additional grounding, else why 6 ground
That's the waveform for something like a phone line (where the phone line has flattened things out a bit), and you'd have no where near the kA kinds of levels. One should be very careful about specif