Author	[Modern View]
awlknottedup 08-26-2012 05:23:52 67.142.168.25 Report to Moderator	I am adding another grounding thread as this is a different take on the question. I am about to put up a 50' radio tower for my amateur radio activities. This is an area of thunder storms, a friend on a ridge has had several hits that caused damage and another lost a house to lightening caused fire. From looking at the trees in this little valley I see no indication of hits right here and in the two years we have been here I have not seen any really close strikes. I have sunk two ground rods about 8' apart outside the room where I have the radios. There is an aluminum plate where all radio grounds are connected and a heavy braided strap to the ground rods. Lightening arresters are on the incoming coax. The tower will be set on a concrete base of about one cubic yard. Rebar will be used in the concrete. From the recent thread on ground rods a mention was made of using the rebar as ground. I had planned on setting 2 - 4 ground rods around the base of the tower. How can I use the tower base rebar for grounding? [Reply]   [No Email]
buickanddeere 08-26-2012 19:34:43 209.240.117.184 Report to Moderator	Re: More grounding questions in reply to awlknottedup, 08-26-2012 05:23:52   There are entire books written on how to protect radio towers from lightening strikes and be back on the air in minutes. The ground cables can not have sharp bends or the lightning will see the bend as impedance and leave the grounding cable. The base of a radio tower needs a dozen or more buried ground cables surrounding it in a radial pattern. [Reply]  [No Email]
PJH 08-26-2012 18:54:50 50.44.245.21 Report to Moderator	Re: More grounding questions in reply to awlknottedup, 08-26-2012 05:23:52   Some of us local hams used to have a 2 meter repeater on the highest hill in the area. Our antenna was down the side of the 195' tower, about 20' from the top. Local business owned the tower and had their antenna on the top. The tower was struck by lightening several times while I was involved with it. The business band repeater always took the brunt of the hit. After all of the strikes, we only had to replace the fuses in the ham power supple, and we were back on the air. Each leg of the tower was bonded to a seperate ground rod, and the guy anchors each had their own ground rod. It was not unusual to find the #6 solid copper bonds completely vaporized after a strike. I'm scared to death of lightening. Every time a big storm comes up I wonder what would possess a man to string up a bunch of wire high in the air, seemingly as an invitation for God to exact His revenge on my misdeeds. [Reply]  [No Email]
KEB1 08-26-2012 17:21:31 184.99.249.103 Report to Moderator	Re: More grounding questions in reply to awlknottedup, 08-26-2012 05:23:52   Do not use the re-bar in the concrete base to provide a lightning ground, unless you like the idea of a lightning strike blowing the base apart. You should have at least one rod near the base of the tower but not embedded in the concrete. Run a large conductor from the tower itself to the rod...#2 AWG is a good size. Try to make gradual bends to minimize series inductance. It's also a code requirement to bond the tower rod to the building safety ground in order to prevent large voltage differences due to resistance in the ground in the event of a lightning strike. It's also a good idea to bury the coax cables from the house to the base of the tower, which tends to limit the amout of lightning energy that propagates along the cable. Bond the cable shields to the tower at ground point also to limit inductive coupling. Keep in mind that so-called "lightning suppressors" are really nothing more than voltage clamps (diodes and/or spark gaps) that limit the voltage between the center conductor and shield of a coax cable. None of them can carry the actual lighting current, and none of them limit induced voltage between coaxial cable shields and surrounding conductors. Here's a link to a site where you can download a PDF that discusses Article 810 of the National Electrical Code, which defines the minimum requirements for antennas and towers. There's also a bunch of info on lightning protection for amateur radio towers at the ARRL website (www.arrl.org). You don't have to be a member to see a lot of the info. Keith Article 810 [Reply]  [No Email]
awlknottedup 08-26-2012 17:49:45 67.142.168.25 Report to Moderator	Re: More grounding questions in reply to KEB1, 08-26-2012 17:21:31   Thanks for the reply. That article answered several questions. [Reply]  [No Email]
George Marsh 08-26-2012 15:18:45 50.104.200.175 Report to Moderator	Re: More grounding questions in reply to awlknottedup, 08-26-2012 05:23:52   awlknottedup, I can't remember who discovered that charges will bleed off pointed objects. Don't know anything about radio towers. Wondering if it would be a good idea to put a few pointed lightning rods on tower? I can tell you lightning does what ever it wants. I've seen it hit an outside grounded metal light fixture, come inside the house and a damage the wire going to the switch before it finally found the grounding wire. I had an underground wire next to metal fence posts and tree roots. The wire was blown out of the ground, parts of the wire was pulled apart, parts of the wire went up in smoke. The lightning came in the house, sparks game out of the electric range, damaged the microwave and TV. It also required a change of underware. Had 8 cows killed. Lightning struck a tree and went throught the roots killing the cows. The list could go on, but you get the point. All the grounding rods in the world won't keep lightning from doing what it wants to do. Just my opinion. Sure it will not be shared by all. If we could control lightning it would make a heck of a lot of energy. George [Reply]  [No Email]
John T 08-26-2012 08:59:38 216.249.82.117 Report to Moderator	Re: More grounding questions in reply to awlknottedup, 08-26-2012 05:23:52   When I designed (remember its been a while) and there were more then one readily available approved "grounding electrodes" such as metal water pipes,,,,,,,,Building structural steel,,,,,,,Concrete encased rebar,,,,,,,,ground rings,,,,,,,,,supplemental "made electrodes" such as driven rods,,,,,,,,WE BONDED THEM ALLLLLLLLLL TOGETHER WITH A CONTINUOUS NO. 4 BARE COPPER GROUNDING ELECTRODE CONDUCTOR which ran to and was bonded to the incoming Utility Neutral at either the weatherhead riser or the meter base or the main panel. So if all your tower grounds and plates and supplemental made electrodes (driven rods) could be bonded and that also used as the "grounding electrode system" Id suggest that for "single point grounding" as a good method to satisfy NEC grounding plus help with lightning and surges BUT YOU MAY WANNA CONSULT ARRL about the antenna grounding with which Im not very familiar Sorry, not being a radio or ARRL kinda guy but more familiar with NEC thats the best I have to offer so NO WARRANTY (especially as far as ARRL) John T [Reply]  [No Email]
Stephen Newell 08-26-2012 08:50:55 66.53.82.37 Report to Moderator	Re: More grounding questions in reply to awlknottedup, 08-26-2012 05:23:52   If it were me I would install a separate copper ground rod just for the tower. [Reply]  [No Email]
David G 08-26-2012 07:12:09 205.215.206.18 Report to Moderator	Re: More grounding questions in reply to awlknottedup, 08-26-2012 05:23:52   You will probably want a grounding mat for the tower. Check with AARL guidelines. [Reply]  [No Email]
tech4 08-26-2012 06:48:28 72.15.69.39 Report to Moderator	Re: More grounding questions in reply to awlknottedup, 08-26-2012 05:23:52   From a guy that has had a tower hit - be sure to bond the tower to the house ground! I had a tower that was grounded with rods but not bonded to the house ground. One strike hit the tower and flashed over to the house. One coax was crossing a grounded 3/4 copper water pipe and burned a large hole in the pipe. I got lightning rods after that and every thing in my house and near my house is bonded to a burried copper ring around the house. No strikes since. [Reply]  [No Email]
awlknottedup 08-26-2012 06:58:35 67.142.168.20 Report to Moderator	Re: More grounding questions in reply to tech4, 08-26-2012 06:48:28   We are thinking of building a house and if we do, I will have a buried copper ring with ground rods. I also plan to run a heavy ground line from the tower to the existing house. The separation is about 50'. [Reply]  [No Email]
tech4 08-26-2012 09:10:49 72.15.69.39 Report to Moderator	Re: More grounding questions in reply to awlknottedup, 08-26-2012 06:58:35   Don't depend on a grounded antenna switch to save your equipment. The strike damaged my switch and tuner plus one transceiver that was connected. I disconnect all coax when not in use. I have had 2 damaging strikes before my lightning rods. The first strike hit a small down spout from the gutter and arced through a brick wall in to the electrical wiring and caught a bed on fire. You better believe my gutters are bonded to the lightning rod system now. When it hit the gutter there was no damage to the tower or any other equipment in the house other than from the fire. [Reply]  [No Email]
awlknottedup 08-26-2012 10:09:51 67.142.168.21 Report to Moderator	Re: More grounding questions in reply to tech4, 08-26-2012 09:10:49   The same happened to a friend. The hit on a copper scupper arched into the electrical wiring for an outdoor light setting the corner on fire. They were home and were able to call the fire department in time. [Reply]  [No Email]
MarkB_MI 08-26-2012 06:16:16 75.219.124.201 Report to Moderator	Re: More grounding questions in reply to awlknottedup, 08-26-2012 05:23:52   Rebar can be used for grounding because concrete slabs and foundations have a lot of surface area, so they offer good conductivity to ground. I doubt your tower base has enough surface area to provide a good ground. But I don't suppose it will hurt to clamp a grounding wire to your rebar, and clamp the other end of it to whatever bolts or brackets your tower will attach to. [Reply]  [No Email]