Grounding Do's Don'ts & Why Part 3

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by AI5DH, Mar 19, 2012.

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  1. WA7PRC

    WA7PRC Ham Member QRZ Page

    Any opinion you get on a forum may or may not be correct. To be absolutely certain before possibly wasting time/money, check with a licensed electrician in your area. FWIW, mine required ≈ 40' of wire, and had to pass under an existing concrete slab (about 50' total). That was the shortest route.
     
  2. AI5DH

    AI5DH Ham Member QRZ Page

    Yes Sir all it takes is work. I started out as kid with a Electrical License, went to college got a BSEE, then obtained my PE with over 30 years experience and design of Protective Grounding Systems for Electrical Distribution and Sensitive Electronic Systems. Do a lot of work for Telephone Wireless and Commercial Broadcast. Even sit on a Board of the NEC Code Making Panel.

    You simply dig a trench from the cable entrance of your Shack where the Ground Rod is, to AC Service Ground to bury a BONDING CONDUCTOR that Bonds the Ground Rod at your Shack Entrance to the Rod of the AC Service Ground. All it takes is work and proper termination techniques.
     
  3. KC9WUK

    KC9WUK Ham Member QRZ Page

    Excellent posts! I'm also a "professional", but do not have the time in that you do! I've been in PTP and PTMP radio for about eight years. I'm the network admin for a small independent telco and WISP. FCC licensed on band 4 and band 17. Just migrated to LTE gear.

    I'm in the process of setting up my home shack now and am very happy to have your info. I know quite a bit about lightning and power grounding, but zero about RF ground. Thanks for straightening me out!
     
  4. AI5DH

    AI5DH Ham Member QRZ Page

    Rf and Safety Ground are two completely different subjects. They do have something in common, they both must be bonded together.
     
  5. AI5DH

    AI5DH Ham Member QRZ Page

    They are called Bullet Bond made by 3M . Grainger and other Electrical Supply Houses that handle Telecom products have them in stock. For hard line there are sheath Ground Straps made using braided and a Hose type clamp to fasten it to the sheath.

    However best practice is to use a Surge Protection Block where the coax enters the shack. The Ground Block looks like a female threaded PL259 splice mounted on a base with a terminal to connect a ground connection too. Strapping the sheath is employed where the coax leaves the tower.
     
  6. W2EM

    W2EM Ham Member QRZ Page

    Some years ago, I had a computer wiped out from a municipal electrical power surge and outage. The desktop computer was shot and I had everything hooked up to a Tripp-Lite surge protector with the $50,000 insurance. Short story, neither the power company or Trip-Lite would cover anything, both denied responsibility. I was SOL. :mad: Sort or sours me on Tripp-Lite now. I wouldn't be real confident in getting anything from the insurance.
     
  7. WK4O

    WK4O Ham Member QRZ Page

    I just came across your posts here about grounding and appreciate all the information! I do feel the need to ask what is quite possibly a dumb question... You mention in Part 3 here that all Primary Surge Arrestors should be located outside the building at the entry point and Secondary Surge Arrestors inside the shack, just where everything enters the shack.... Could you provide some specifics about what constitutes a Primary vs Secondary Surge Arrestor? i.e. Would I put something like a PolyPhaser on the outside and the inside, or one or the other? If not both, which place, inside or out?

    Also, the single point ground panel would need to physically be in the shack, not simply on the inside wall where everything comes into the building. To be more specific, all of my coax, power, etc. enters the house on the back basement wall, and my shack is located in the basement on the front wall of the building. So would I want my single point ground panel to be in the shack with a heavy copper or aluminum wire running from that panel back through the entrance point in the wall to the ground post; OR would I want to put the SPGP on the inside of the wall where everything enters and run all my chassis grounds, etc from the shack back to that wall? I hope this makes sense... If not, just ask for clarification or email me... My email is available if you look me up here on QRZ...

    73,

    Matt, KK4NTM
     
  8. K6CFC

    K6CFC Ham Member QRZ Page

    LJW, would it be possible for you to post some photos of your setup? You said you are using a copper buss bar with isolators, but then later stated that all surge protectors (which I assumed to also mean the Tripplite units), are to be physically mounted to it. I'm struggling with a visual of that. This has been a great series of threads, and I have learned a lot so far, so thanks to all.
     
  9. W5OXL

    W5OXL Ham Member QRZ Page

    Ground Installation Issues

    I haven't seen this addressed in these threads on grounding. I live on about 9 acres in an area of somewhat sandy soil. Specifically I live on the Woodbine Sands formation just south of Fort Worth, Texas. The soil is a mix of sand and clay going from essentially "sugar" sand on the east side of my property to somewhat more clay/sand on the west side. There are a couple of rock outcroppings around the place. My ham shack is near the east side (See my call sign here on QRZ). From previous articles it would appear that I need a number of ground rods to get a good connection.

    The problem that I am having is that I can only drive grounds rods about 5 feet into the ground before I apparently hit rock and can drive them no further. In a past position doing ESD ground work for the company I worked for, I was introduced to MIL-HDBK-419 "Grounding, Bonding and Shielding for Electronic Equipment...". It advised to drive ground rods in at an angle if there was solid rock too close to the surface to drive them vertically. I have been able to access some of the NEC and it seems to be moot on this. Is this acceptable for for safety and lightning grounds?

    Overall, the question at hand is what kind of tactics can be used by the radio amateur to get a good ground installation when subsurface rocks prevent driving the ground rods in vertically?

    Bill, WD5HHH
     
  10. AI5DH

    AI5DH Ham Member QRZ Page

    Certianly, and permissible per NEC. In fact per NEc or any other document that pertains to lightning and grounding protection no ground rods are required at all. Truth be told ground rods are fairly poor.

    The two best ground systems are what the NEC calls Concrete-Encased Electrode and Ground Rings. People even professionals in the industry get too hung up in the ground impedance number. You will see many manufacture documents that specify 5 ohms or less which is just plain silly and meaningless. I have called Motorola, Nortel, Alcatel-Lucent and the 3 major telephone companies out on it and why they specfy 5 ohms or less. Not a single one of them can come up with an answer other than a couple of old timers that came from Bell Labs many moons ago from the early 1900's when the Telco actually used earth as a conductor to operate your ringer in your telephone. Back in the very early days the Teloc applied Ringing voltage from Ring to Ground on a 3-wire telephone circuit. Today the NEC and industry forbid using earth as a conductor for consumer applications. Only companies that use earth as a conductor today are Electric Utilities. At low voltages below 1000 volts earth is useless as a conductor.

    One young engineer from from ATT one day was stating how wonderful 5 ohm ground was at protecting both equipment from lightning and offering personnel protection from electrical shock. He was ripe and primed for a fight when I called him down on it. I first asked him how the impedance was measured (I already knew the answer)? Like all smart engineers or electrician replied with a "3-Point Dead Fall Potential". I then asked him what Frequency does the 3-Point use? He replied with the right answer again of "Power Frequencies from DC to 300 Hz". I ad this sucker hooked and ready to real him in.

    My next question to him threw him for a day or two because he had to go look it up. I asked what was the impedance of a single 750 MCM stranded copper conductor 10 feet in length at a frequency of 10 MHz? Well two days later he came back and said around 2000 Ohms which is the right answer. I agreed, then asked at what frequency range does the majority of Lightning energy is contained in? He had no answer, so I had in my possession a couple of books that had the answer of between 1 and 100 Mhz. So I asked him if we could agree to use 10 Mhz for a model and he said certainly.

    So I then said we have a 5 Ohm Ground Electrode obtained and measured with a 3-Point Dead Fall Potential and connect the building electrical system using a standard 750 MCM stranded copper cable. I then hit him with reality. The building takes an lightning strike, what is the total impedance from the service entrance to earth through the 750 MCM to the Ground Electrode. He said that was easy to answer a simple series resistance of 5 ohms + 2000 Ohms = 2K Ohms. You should have seen the look on his face when he realized what he had just said.

    I then told him no let's be realistic. What is the real impedance of his 5 Ohm ground at lightning Frequency frequencies. He could only say something many magnitudes higher then the 5 Ohm for power frequencies. I just smiled then kicked his but with Four more questions. First question was, what voltage does your equipment operate at? Answer 48 volts. Second question how many amps of fault current are induced at a 5 ohm dead bolted fault? Answer around 10 amps which is close enough. Third question what was the smallest breaker/fuse size was in the battery distribution cabinet for his equipment? He said 20 amps. Forth and finale question was what value does a 5 Ohm facility ground bring and how does it protect personnel? . He did not answer, hung his head, and walked away.

    20 years later I seen this guy at the NEC conference in LA CA. He remembered me and we had a good laugh. He said after our conversation he went all the way up to ATT top engineers and finally found one ole timer that had retired who knew where the 5 Ohm requirement came from. It had nothing to do with lightning whatsoever. He discovered the truth it was the needed for ole ringers to ring telephones, and telegraph clickers back from the Civil War.

    Now you know the rest of the story. :cool:
     
    W1ADE and MM0HVU like this.

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