CONFUSED ON RF/AC GROUND
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| May 30th 2012, 19:31 | |
KJ4TOFTotal Topics: 0 Total Posts: 0 |
I've only been a ham for about 2 years. I live in florida (lightening capitol of the world). Let me begin by explaining how my ac ground is set up from the meter. Instead of going to a copper rod in the earth directly below it, it has heavy guage copper wire that goes up the wall from the meter into the attic, then through the attic to the other end of the house (about 60 feet) and down the garage exterior wall into the cement floor of the garage. I've never seen a set up like that, but then I've recently moved to florida too. Up until now I've never really concerned myself with lightening because I run a dipole wire, and I always disconnect it outside when it storms (except when I forget to either unhook it , or hook it back up afterwards). To connect to my house ground i would have to run a wire all the way around the side of the house into the garage to access the house ground rod. For RF ground I use grounding strap to a copper tube with hose clamps. The copper tube is mounted to the back of my desk. No daisy chaining! The copper tube is then connected to an mfj window feed ground terminal via 1 inch grounding strap. On the exterior side I have copper tubing terminated (clamped) to an 8 ft copper plated ground rod. The total distance is about 6 feet. Am I doing it right? Any suggestions? Thanks in advance! Bill KJ4TOF |
| May 31st 2012, 16:19 | |
W1VTSuper Moderator Total Topics: 0 Total Posts: 0 |
It sounds like a Ufer ground, in which you encase at least 20 ft of #4AWG wire in concrete, close to the ground (2 inches). http://www.aps.com/files/_files/pdf/ESPServices/700.pdf This document has detailed drawings of a Ufer ground. http://www.esgroundingsolutions.com/about-electrical-grounding/what-are-some-different-types-of-grounding-electrodes.php This page has pictures of different grounding electrodes The reason for bonding grounds together is that if they aren't, lightning will often cause a lot of damage jumping from one ground to another. I've heard of hams that have had equipment damaged that way, even though the power plugs and antennas were disconnected. Zack Lau W1VT ARRL Senior Lab Engineer |
| May 31st 2012, 17:06 | |
K0BGTotal Topics: 0 Total Posts: 0 |
Ufer grounds are common in Florida, and the condo where I stay has one. As Zack alluded to, tying all of the grounds together reduces the possibility of creating a ground loop (differential in ground resistances). Sometimes it can be an expensive pain, but it is very good insurance. My 6BTV has been hit several times, with no damage done. Its radial field is connected to the entrance and user grounds in several places. |
| May 31st 2012, 17:37 | |
W0BTUTotal Topics: 0 Total Posts: 0 |
I'm not so sure about this design. How long has this type of "ground" been in use? Long enough to prove its reliability(?) I hope. I thought cured concrete was an insulator. How does this compare to a good copper-clad ground rod driven into the earth? And it seems to me that if lightning were to follow that wire buried in that concrete foundation on page 3, that's a recipe for disaster. I'll stick with 8' ground rods for service grounds and lightning protection, thank you. 73, Mike www.w0btu.com |
| May 31st 2012, 17:41 | |
WA0CBWTotal Topics: 0 Total Posts: 0 |
AC and RF grounds can be very confusing. An AC ground is usually found at the entrance panel or the electrical meter. This can consist of a ground rod or any other NEC recognized ground (including the UFER ground described above. An RF ground can be thought of as the radials under a vertical antenna or a counterpoise under a long wire antenna. The NEC says that ALL grounds should be connected together, AC, RF, Station, and any others such as the CATV, Telephone, and the copper water pipe in your house. Taking it a step farther all the grounds should be connected to a "single point" ground. Commercial installations use the single point ground concept to prevent flash over between different length runs of ground wire. Usually the easiest single point ground location is the house electrical ground. This means that all the different grounds described above should be connected together at the house electrical ground rod. A good grounding primer is the Motorola R-56 manual. It describes many different configurations to arrive at a single point ground. As mentioned by Zack and others most lightning damage is caused by flash over between grounds of different potentials. Simply unplugging your equipment or disconnecting your antenna may not prevent lightning damage from flash over. Bill ARRL Technical Coordinator - Kansas Section |
| May 31st 2012, 18:40 | |
W0BTUTotal Topics: 0 Total Posts: 0 |
Thank you for that. I just downloaded it from http://radioandtrunking.com/downloads/motorola/R56_2005_manual.pdf 73, Mike www.w0btu.com |
| May 31st 2012, 21:37 | |
KJ4TOFTotal Topics: 0 Total Posts: 0 |
Hmmmmm, I guess what's puzzling me the most right now is why they put the electric meter on the end of the house farthest away from the ground rod/concrete garage floor. I don't like the thought of a lightening surge traveling through my attic on it's way to ground. Thanks for all the input. |
| May 31st 2012, 22:14 | |
W1VTSuper Moderator Total Topics: 0 Total Posts: 0 |
The biggest problem I can see with Ufer grounds is that they need to be installed at just the right time as a house is being built--there is no cheap and easy way to add one after the foundation has been poured! Zack Lau W1VT ARRL Senior Lab Engineer |
| Jun 1st 2012, 13:30 | |
KJ4TOFTotal Topics: 0 Total Posts: 0 |
This is a new construction house. Brand new, go figure! |
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