[TenTec] OT: Lightning and Grounds

Sat Jul 2 00:22:30 EDT 2005

While I don't have a current copy of the National Electrical Code in front of me, it does (or at least did several years ago) call for the bonding of all "grounds" on the premise. My training was in a course in "Grounding and Lightning Protection" which was held in Florida. My former employer (a very large, national insurance company) operates data centers, communications equipment, and other sensitive electronic equipment in thousands of sites around the US. The buildings range in size from old service (gas) stations, to multi-story, multi-million square foot complexes. Many of their buildings have air terminals, a ground ring, and some have ground mats in addition to the requisite driven rods and water main bond.

The Corporate headquarters tower building roof top is 197 feet above ground with air terminals. I operated both commercial and amateur radio equipment into antennas extending more than 12 feet above the air terminals for more than twenty years from that site with no adverse effects from lightning or static dissipation.

 For example, the N9PE DX Spider node operating on 144.91 uses a Kantronics KPC-3 TNC, an Alinco DR-1200, 35 feet of half inch Heliax® and a VHF-UHF Cushcraft Ringo. The antenna is mounted and bonded to building steel, the feedline shield is bonded to building steel near the antenna, the feedline penetrates the roof pan through a metallic sleeve (no bond which creates a high impedance to any energy on the outside shield of the feedline) then it is terminated on a Alpha Delta protector before the radio. The A-D protector is bonded to a grounding plate attached to building steel (support column) and a double run of 4 ought that terminates at the building ground mat 190 feet below. The power to the radio and TNC are from a common 12 VDC supply, via a small UPS, connected to a common 120 VAC circuit which uses building steel for the "mechanical ground".  This is a mid-west location with lots of lightning but we've not had any equipment fail due to lightning for over twenty years.

The NEC philosophy seems to be "bond all your grounding conductors together so there is no step voltage or voltage differential; use lots of grounding rods, mats, pipes, rings but keep them bonded together; provide low impedance (that's RF current folks) paths to ground for lightning with high impedance (to the lightning) signal paths to your equipment." And finally if everything is bonded together via the ground conductors, and  everything rises in voltage at the same time from a direct or near hit, no transit differential, no sparks, no damage...... that's the theory and it does seem to work. Or maybe I was just very lucky for twenty plus years.

73
Gary - AB9M - www.csm-gh.com<http://www.csm-gh.com/>

  ----- Original Message ----- 
  From: Robert & Linda McGraw K4TAX<mailto:RMcGraw at Blomand.Net> 
  To: Tentec<mailto:tentec at contesting.com> 
  Sent: Thursday, June 30, 2005 10:00 PM
  Subject: Re: [TenTec] OT: Lightning and Grounds

  Carl's comments are really the only really safe way to handle the issue. 
  However, in many cases, such as remote radio installations or repeater 
  installations the approach of disconnecting is not a reality.  At the same 
  time, proper grounding is a reality.  I strongly subscribe to the practice 
  that all grounds being served by a common electric service must be bonded 
  (connected) together.

  Several have asked about why disconnecting the antennas and leaving the 
  ground connections caused a problem.  Look at it this way as a simple test. 
  Start with 2 driven grounds say some 20 ft apart.  Measure the resistance 
  between the two.  Then connect the two driven grounds together with a piece 
  of #8 or larger copper and again measure the resistance between the two. 
  Well of course, the connection between the two connected together will have 
  a much much lower resistance.  Now then, apply ohms law, E = I*R.  You have 
  2 values of R to use, one without the bond wire and one with the bond wire. 
  You choose an arbitrary value of current  "I", say 100 amps.  What's the 
  voltage between the two grounds?  Now, say your radio equipment is connected 
  to one ground and the AC mains is the other.  Thus without being bonded 
  together the difference in potential will be flowing from your radio ground, 
  to your radio equipment through your 3rd pin ground or from the chassis to 
  the neutral via the power transformer insulation.  Even though the equipment 
  is off.  Result:  damage to the radio and if the surge is large enough, 
  damage to the house.

  In the example above I will use a R value of 25 ohms for the resistance 
  value of the un-bonded grounds and an R value of 0.1 ohm for the bonded 
  system.  In each case the current is 100 amps.  The voltage between the two 
  un-bonded rods would be 2500 volts and for the bonded configuration the 
  voltage would be 10 volts.  Which case would you prefer?  Most power 
  transformers have a test voltage rating, primary to frame of 1500 volts.

  For the comment of the power company not requiring a driven ground, I don't 
  think this complies with the NEC.  Perhaps someone that is more familiar 
  with the NEC can contribute to the statement.  To that end, some have said 
  to use the water line as long as it is metallic.  Many houses use copper 
  inside but have plastic or PVC to the meter.  No ground exists in this 
  configuration.

  I realize that this is not really along the topic of Tentec radios, but does 
  apply to Tentec radios and all other brands as well.  Thanks to the 
  moderator for allowing the discussion and post.  To that end, I have a nice 
  paper which I have presented at several conferences and has been published 
  in several journals.  It deals with "Lightning Protection for the Home and 
  Station".  It is free for the asking.  It is in Microsoft Word format and 
  the file size is about 175K.

  If you wish further dialogue on the subject contact me direct.

  73
  Bob, K4TAX
  RMcGraw at Blomand.net<mailto:RMcGraw at Blomand.net>
  171 Grandview Dr.
  Sparta, TN 38583

  ----- Original Message ----- 
  From: "Carl Moreschi" <n4py at earthlink.net<mailto:n4py at earthlink.net>>
  To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com<mailto:tentec at contesting.com>>
  Sent: Thursday, June 30, 2005 9:25 PM
  Subject: Re: [TenTec] OT: Lightning and Grounds

  >I completely disconnect all my equipment when a storm comes.  That means
  > disconnecting all my electronic equipment from the antennas, power, phone
  > lines, and GROUND.
  >
  >
  >
  > Carl Moreschi N4PY
  > Franklinton, NC
  > ----- Original Message ----- 
  > From: "John Rippey" <w3uls at 3n.net<mailto:w3uls at 3n.net>>
  > To: <tentec at contesting.com<mailto:tentec at contesting.com>>
  > Sent: Thursday, June 30, 2005 10:13 PM
  > Subject: [TenTec] OT: Lightning and Grounds
  >
  >
  >> K4TAX wrote:
  >>
  >> "George, I do hope you have those driven grounds bonded to the AC mains
  >> ground and all other driven grounds around the property.  Failure to do 
  >> so
  >> will produce a step voltage between two different ground during a near-by
  >> lightning strike.  Equipment connected between the two different grounds
  >> will then share the current flowing between the two different grounds.
  > The
  >> result is that one can observe extensive equipment damage or worse."
  >>
  >> 1. I've often wondered what would happend with a lightning strike nearby
  >> and everything connected together (as at my QTH): coax feed line ground
  >> block; phone; AC main; AC outlet strip for radios; radios' bus bar 
  >> ground.
  >> This may be dumb, but why would not the electrical charge from lightning
  >> come bounding into the shack via the common grounds? Disconnecting the
  >> antenna leads at the radios does not seem to be a protection since the
  >> radios' grounds are common with the outside grounds.
  >>
  >> 2. The local power company told me a couple of years ago that the code
  >> around here anyway no longer requires installation of a ground rod at the
  >> Main for a new house. What gives here?
  >>
  >> 73,
  >> John, W3ULS
  >>
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