Here's a brief summary of the grounding on my tower as it stands today. It's not perfect, it's not even ideal. It's a major compromise.
I ran a 2" copper strap from one tower leg to a ground rod about 20' away. The strap is buried underground, but only about 4 inches deep. The reason it is so shallow is due to limestone being 6" below grade. The ground rod is a standard 5/8" diameter copper clad rod, 8 feet long, made by Erico. The connection to the tower is a #2 copper wire pigtail that was brazed to the strap with Harris Stay-Silv 5 brazing rod, the wire is then clamped to a tower leg with a bronze ground clamp. I purchased the brazing rod at a local welding supply house. The connection to the ground rod uses a similar pigtail, which is then Cad-Welded to the ground rod using a "One-Shot" purchased from Tessco.
A second ground wire is connected to the tower the same way, then the strap runs to a ground rod, connected with another pigtail. The strap continues on and will eventually be connected to the single point ground for the coax entry panel, which is still a work in progress. There just hasn't been enough time…
My main electrical service is grounded, again via a #2 copper wire, to an existing 8' ground rod at the electrical meter. There I have a 4-way Cad-Weld One Shot, with a #6 wire running to another ground rod for the telco ground, a #6 going to yet another ground rod, and a #2 going to the ground rod mentioned in the previous paragraph, this wire provides the REQUIRED bonding connection between all the services and the tower. It can not be stated enough that this connection is extremely important. Do not skip the bonding step.
The electrical service panel is protected with an LEA whole-house surge protector. The telephone line has secondary protection after it enters the house, just inches from my electrical panel. I'm using Polyphaser IS-MPT-200 protectors. I like these because they are cheap, and they seem to work very well. [edited to add: I've been told these are no longer available] I have a small punch-down block for the phone lines so these work nicely for me. I'm using two because my voice and ADSL come into the house on separate pairs, with a telco provided splitter at the network interface device. All coax will be protected by Polyphaser units, and I'm looking for a suitable rotor protector. Polyphaser makes one, but its rather pricey at around $150, half the price of the entire rotor! ICE also makes one, but I haven't bit the bullet and ordered one yet.
At some point, I'll draw a picture of all of this so it makes more sense.
One additional thing I did was to have my entire re-bar cage welded together, and welded to the anchor bolts for the tower. In the event of a lightning strike, their will be no opportunity for arcing inside the concrete foundation. This also allows the foundation to act as a "Ufer Ground".
There will be more to be said about lightning protection later on.
Ufer ground, I had never heard the term before, I had to read up on it. It’s a pretty smart way to augment your grounding with materials you were already using. How did you decide how much steel to use to avoid concrete flaking/decay?
Man the Limestone has been the bane of this project eh? Do you know if it’s good ground? It wouldn’t seem like it would be as effective as soil, but that is a guess. If the water table kept the limestone saturated it might be a fairly good ground. Huh, I’ll have to go look that up next 🙂
I learned of the UFER a little over 10 years ago when I started studying up on grounding for tower sites after I tired of chasing behind storms fixing the destruction from lightning while I was working in the cellular business. My employer didn’t understand lightning protection at all, and while it was great job security, the 3am trouble calls were getting tiresome. I went from multiple failures per month at one site to none over the next year until I left that job.
As for how much steel to use, I went a bit overboard. A friend that does lots of ham towers did the rebar and welding, so I went with what he recommended, which was more than what Rohn specified in their foundation drawings. I figured more than the minimum is good.
If I never saw any more limestone it would be too soon! It’s a HORRIBLE conductor. Something like 1000 times more resistive than normal soil. That’s not good at all.. But what can a guy do? Closer to the house it’s all backfill from when the basement was dug, so I’m trying to drive rods about 36-42 inches from the foundation, where there’s no rock.
Now, if I wanted the perfect ground I would run 2 inch strap all the way around the house, with 10′ ground rods every 20 feet or so, and 3 radials coming off the tower itself with 3 ground rods on each. But that’s not practical in a residential setting, nor is financially feasible. So compromises have to be made. I hope to add to the grounding in the spring when I have a bit more money, and time.