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Author Topic: Grounding Question  (Read 4154 times)
AC2EU
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« Reply #15 on: April 26, 2013, 07:38:23 AM »

NEC code requires that the shield be grounded before it enters the building, preferably at the same place as the AC power ground
Take notice of CATV grounding blocks. Same concept, but usually poorly executed.

If the power ground is a distance from the coax ground, they need to be bonded together with #6 AWG or better. sometimes with a system underground rods along the way, depending on your situation.
There is not always a simple solution. Some grounding systems can be expensive. ( better that than dead... !)


Consult an RF engineer or the  NEC book for proper methods to use at your site.


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W6EM
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« Reply #16 on: April 26, 2013, 05:15:32 PM »


Water pipes for safety grounds are no longer per NEC because of the widespread use of plastic pipe.  Even if all the pipe in your house is metal, you don't know what the utility used out to the street so your "pipe ground" could essentially be floating in the structure.

Before relying on any grounding electrode, one should know about it and if at all possible, measure its true ground resistance.  If a metallic water pipe has sufficient burial in earth or concrete, it is an adequate ground.  Just as are reinforcing steel bars used in concrete.  Of course, if you had copper or iron pipe within the structure and absolutely no copper or iron pipe underground, then it would be worthless.  Frankly, I would recommend determining what the existing residential grounding electrode is.  Which one of the above is it?  His might very well be his water pipe.  Supplementing it with properly interconnected supplemental ground rods would be fine.


 
Quote
From an RF point of view you are merely effecting the above, turning your water pipes into a lossy antenna.

If you have an unbalanced coax transmission line from your transmitter, then perhaps you might have some radiation from what is intended to be a grounding conductor, especially if a significant fraction of a wavelength.  But, ideally, with a properly applied choke balun at the rig or tuner output, you'd force equal currents and dispel any other RF current paths, including your power cord grounding conductor to the convenience outlet, supplemental wire ground, pipe ground, etc.  If you believe that the NEC is a "bible," requiring no interpretation, well, you are misinformed.  That same book considers a grounding electrode resistance of 25 ohms or less as being adequate.  A fool's errand, for sure.

Quote
  Yes, sometimes this helps because it may solve a symptom but the better way to fix it is to solve the common mode issue.

Perhaps, Mark, if you had been a tad more definitive in what you meant by "common mode issue," it would have been more instructive.  Ideally, common mode currents in a transmission line should be inhibited.  And, 1:1 current baluns on coax feedlines do this very well.  Simply wrapping a few turns around a Mix 43 or 61 ferrite balun will help insure that common mode currents are suppressed.  Including both RF and lightning impulses.  The trouble with them, though, is that they don't allow for equally grounding both sides of a balanced load like a 50-75 ohm typical feed impedance dipole.  Voltage baluns, however, do that very well.

73,

Lee

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K1PJR
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« Reply #17 on: April 28, 2013, 09:10:42 AM »

Mike

My shack is also on the second floor.  I do not ground my equipment.  As mentioned before there are three types of grounds one of which is an RF ground.  That RF grounding takes place outside, not in the shack.  Running a thick cable from your equipment to a ground rod will only cause the ground wire to become an antenna if you do in fact have RF in the shack.

Proper antenna installation, radials (if needed), chokes, baluns etc., these all help in keeping the RF at the antenna and off the transmission line and therefore out of your shack.  There's just way too much emphasis in regards to grounding equipment.  If your outlets are grounded, you have a lightening ground and you do your homework with your RF ground then your all set. 

I'm far from being an expert in this area.  There is a lot to read regarding grounding and it can be confusing.  There are many who feel this necessity to run massive pieces of copper from their equipment to a massive ground rod.  IMHO it's unnecessary.  I have a 120 ft longwire with a unun at the feedpoint.  I run 100 ft of coax and the braid also acts as the counterpoise.  I also attached several radials and I have a choke installed at the point where the coax enters the shack.  The choke keeps any stray RF out of the shack.  I have zero issues when operating and no RF in the shack.

Good luck.
73

Phil
K1PJR
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K1PJR
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« Reply #18 on: April 28, 2013, 12:06:20 PM »

Mike

Read this article:

http://www.eham.net/articles/21383

Phil
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K4SAV
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« Reply #19 on: April 28, 2013, 03:00:18 PM »

Beware of recommendations stating little or no grounding is required, then that person stating they have done that for years and never had a problem.  Invariably the reason they have never had a problem is because their antenna has never been hit by lightning.  If that person posts a lot, you can usually find other posts by that person and find them saying they have never had a lightning strike, but they won't tell you that when recommending their grounding approach.

Grounding for lightning protection should all be done OUTSIDE the house.  If you do that properly, you don't have to worry about grounding your rig.  It will have a ground connection by the coax and the AC plug anyway.  Run a ground wire to your rig if it makes you feel better but it isn't really necessary. 

The last thing you want to do is plan a system where the lightning current runs thru your house to the rig.  If you don't have lightning current running thru your rig, then there is no need for a big grounding cable run from the outside ground to the rig, and there is no need for an elaborate grounding panel behind the rig.  HOWEVER if you do that grounding outside incorrectly, the lightning current WILL go thru your house regardless of what the grounding is behind the rig, and you will probably have major damage.

Notice that with proper grounding outside, there is no requirement that the station be located anywhere in particular inside the house.  Second floor is fine.  My station is on the second floor and I have a 45 ft run inside the house to the entrance panel which is located on a wall next to the AC power entrance panel.  My tower gets hit 2 to 3 times per year average and no damage so far (since putting the tower up 8 years ago), but I also have a good grounding system outside the house.

Jerry, K4SAV
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KD2CJJ
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« Reply #20 on: April 28, 2013, 04:14:46 PM »

Everything you guys are saying makes sense... The article is a good one also! 

now I have a tough question for you.... I just upgraded my rig (went from a IC7000 to FTDX3000)... My common mode current went away.  With the IC7000 no matter what I did I would always have at least little RF in the shack, the grounding helped tremendously.... When I hooked up my FTDX I assumed the same and hooked back up all the grounds... after this thread I decided to unhook them to see if I had better ears.  I did not hear a difference honestly BUT what I noticed is that all my RF issues went away with the new radio!!!!  The RF ground was not needed... So what gives if everything else is the same?
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73

Mike
KD2CJJ
AC2EU
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« Reply #21 on: April 28, 2013, 09:22:02 PM »

Mike

Read this article:

http://www.eham.net/articles/21383

Phil

If it's not important, Why does the NEC have several pages devoted to the grounding RF installations?
I guess people want to find validation, right or wrong, so that they can feel good about a decision that they made.
Heck, there are folks her who will tell you that a G5RV is the only antenna you will ever need! Grin Shocked Huh Huh Roll Eyes
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K1PJR
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« Reply #22 on: April 29, 2013, 12:16:59 PM »

FWIW, I did read the NEC guidelines.  They refer to antenna grounding for both receiving and transmitting.  It refers to grounding of masts and the placement of transmission lines.  This is in line with what I had said.

You have to have a proper lightening ground.  The NEC does mention a suppressor and also grounding a mast.  I don't have a tower so obviously it's not a concern for me. I do use a suppressor.  Either way all grounding should take place outside.  I agree with that.  The original question was how do you ground your equipment if you have a shack on the second floor.  In my opinion you don't have to provided you have a good electrical, lightening and RF ground, the latter two taking place outside.

To prevent damage to my equipment I disconnect the coax.  It's no where near my rig when disconnected.  That's the only way to truly prevent damage. I'm in agreement with K4SAV.  If you take care of your needs outside, you should be fine inside.

Phil
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K4SAV
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« Reply #23 on: April 29, 2013, 05:43:03 PM »

Providing a good grounding system is actually much easier with a tower than with wire antennas.  The tower serves as the lightning path and with several ground rods, most of the current goes into the dirt at the base of the tower.  Some of it goes toward the house on the ground wire and coax lines.  A good common point ground connecting the ground from the tower and the AC ground at the house does the rest of the job, assuming all your antenna cables are also grounded to that point and you have no cables entering the house at other places.

With wire antennas there is a problem.  A coax line or ladderline will not handle a lightning strike.  They will disintegrate.  When that happens, there is no controlled path for the lightning and it will jump to any place that seems like a good ground.  That is usually multiple places on your house.  I have seen this and the results are nasty.

With a tower you can add inverted vee antennas on the tower and it's most likely (not guaranteed) that lightning will hit the higher tower and not the wires.   If the tower is not next to the house and neither are the wires, that offers a little lower probability of having damage if the wires do get hit.

Jerry, K4SAV
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N4CR
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« Reply #24 on: May 05, 2013, 12:45:22 AM »

I have a single point ground. This ground system runs right in front of my shack. At one end of the house, 45 feet north, it connects to the house rod. There are two ground rods driven in that 45 feet. One right in front of the shack. One on the south end of the house, across 15 feet and one at the fenceline. So about 85' in a single line run with the shack in the middle and half a dozen rods. From the daisy chain of grounds, there is a 3' #4 run up to the grounding plate at the shack entrance with polyphasers for both the 2 meter and the HF coax.

From there, there is 275' of coax going down the fenceline and across to the Cushcraft R-8 on a 10' tripod. There is an 11 turn coil of coax on a 5" form 2' from the antenna base in addition to the matching box. That adds ~ 10k ohms of additional common mode choking on 15 meters, my favorite band.

Last Tuesday night, the R-8 was struck by lightning.

The matching box was completely destroyed. Blown to bits is the proper term. I never found the cover and the box is split into pieces. I have ordered a new matching box. After I get that installed, I'll assess the traps and see if they are roasted.

http://i39.tinypic.com/2zy93er.jpg

Back in the shack, the 746pro was still operational in every way, full power out, no funny stuff. I haven't checked the polyphaser, but I have a spare I'll put into service as needed. Hopefully, the coax isn't ruined, it's a long run of LMR-400.

The only other problems were induced currents. Every ethernet port that was connected to a cable of any length over 10' was dead. This has happened before on the long ethernet runs. I'm going to switch all the computers to wifi dongles rather than individual runs and eliminate all those long runs.

A couple of years back, my Diamond V-2000 took a direct hit. Shattered the fiberglass radome into a million toothpicks and killed the antenna dead. No damage to the polyphaser or the rig. The single point ground absorbed it all.

If I do anything, there's a 30' stretch that doesn't have a ground rod driven and attached and I may fix that soon. But right now, this is working good.
« Last Edit: May 05, 2013, 12:48:18 AM by N4CR » Logged

73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
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