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Author Topic: Station Grounding and Bonding  (Read 1685 times)
VE4AAZ
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Posts: 60




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« on: April 05, 2019, 05:02:24 PM »

In the process of  redoing my  station layout of  radios   I  took a  AC voltmeter  reading between  my operating desk thick  copper  buss bar  that is  bonded to a  8 foot  ground  rod  just  out side my  window and the safety  ground on a  duplex wall  receptacle.  I  measured  around  .290  mV.  AC  volts. I  then  plugged  into a 3  prong  120 vac  duplex outlet  the  transceiver  with the  chassis  wig nut under a 1 inch flat copper  braid attached to the  copper   buss bar  and now  my  reading has  dropped to  .105  mV.  AC  on the  Fluke DVMM.
Is it worthwhile to  install a thicker  #4  AWG copper   from the street side  utility water meter clamp ( same as my service  panel uses  for  its service  ground) over  to  my  station  copper  buss bar  to attempt in decreasing the  voltage drop  even  lower?  Thanks  for  reading.

VE4AAZ
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AA4PB
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Posts: 15066




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« Reply #1 on: April 05, 2019, 05:53:59 PM »

I wouldn't worry about that small voltage difference. The grounding pin in the outlet probably isn't exactly equal to the ground rod potential anyway. There may be small ground leakage currents in other devices plugged into the same branch circuit as your outlet.
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Bob  AA4PB
Garrisonville, VA
W9FIB
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Posts: 2529




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« Reply #2 on: April 06, 2019, 04:22:48 AM »

In the process of  redoing my  station layout of  radios   I  took a  AC voltmeter  reading between  my operating desk thick  copper  buss bar  that is  bonded to a  8 foot  ground  rod  just  out side my  window and the safety  ground on a  duplex wall  receptacle.  I  measured  around  .290  mV.  AC  volts. I  then  plugged  into a 3  prong  120 vac  duplex outlet  the  transceiver  with the  chassis  wig nut under a 1 inch flat copper  braid attached to the  copper   buss bar  and now  my  reading has  dropped to  .105  mV.  AC  on the  Fluke DVMM.
VE4AAZ

This difference is the reason behind the NEC code for bonding all ground rods together.
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73, Stan
Wisdom is knowledge you gain after you know it all.
W9IQ
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Posts: 3531




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« Reply #3 on: April 06, 2019, 09:18:31 AM »

Bill,

It is not clear from your description - is your shack ground rod bonded (connected via a low resistance method) to your house safety ground? And are your readings really 0.105 mV and 0.290 mV or do you mean volts?

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
VE4AAZ
Member

Posts: 60




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« Reply #4 on: April 12, 2019, 07:14:05 PM »

Glenn
   I  rechecked with DVM again  and the AC volts  reading before plugging  in transceiver about  .290 Volts AC  between outside  ground  rod connected to  a #4  copper cable  and    duplex outlet safety ground.
Now with transceiver  connected onto  station  copper bus bar using the  rear  chassis  wing nut AND  plugging   into duplex outlet the  DVM drops to .105  Volts  AC.    NOT the .105mV as reported earlier.

My utility water  meter is 18 feet away and is used  for my service  ground , basically asking if I go ahead and   tie in at my utility water  meter  ground back to  my  station ground to  lower the voltage  drop to  less than  .105  Volts AC   is it  worth the effort .

Bill VE4AAZ
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K6BRN
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Posts: 1342




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« Reply #5 on: April 12, 2019, 10:13:18 PM »

Hi Bill:

The AC voltage difference between your AC socket safety ground and your dedicated shack ground is due to coupled noise on the safety ground from the many feet of hot and return wiring the safety ground is bundled with.  The shack ground has a short run and it's wiring is not parallel to any other supply lines with major loads and noise on them, unlike the safety ground.

The trick is to minimize the noise the radio "sees" from the safety ground without making it worse, and also provide a low-impedance path for stray RF to ground through your shack ground.  There is no "perfect" success in this, just degrees of success.  You'd LIKE your shack ground to be short, low impedance at higher frequencies and also bonded to the same reference as the safety ground, and it SHOULD be.  But you will also create a "ground loop" between the safety ground return to the reference point and the shack ground, THROUGH the radio which CAN be problematic.  Some hams have advised cutting the safety ground prong off of of shack items tied to AC.  DO NOT DO THIS.

What will happen, if you have a good, solid, shack ground, is that the low impedance of the shack ground at higher frequencies will help "pull down" the noise voltage on the safety ground, at the radio, at higher frequencies, because THAT path is relatively high impedance at higher frequencies.  And overall shack ground noise will be reduced AND you will have SOME degree of protection from stray RF in the shack

But this will not work very well if the reference points of both the shack ground and reference ground are not bonded together with a connection that is low impedance at LOW frequencies.  Because without this path, the mutual connection between the two grounds will be through the earth (soil) which is high resistance, and the lowest resistance for low-frequency fault currents MAY be THROUGH YOUR RADIO.  Not a good situation.  Hence the need to bond all ground references together.

In addition, you should connect a coax ground block to your shack ground rod and run all coax to this block to ground the shield of the antenna coax before it enters your shack space, which will help keep all potential ground paths into your radio equalized, which is REALLY the intent of this excercise.

DISCLAIMER:  These are my opinions only.  You must study this topic yourself and make your own decisions.  Improper ground handling, like cutting the safety grounds off of AC supply cords can be dangerous.  They're there for a good reason.  The ARRL has a good guide to grounding available:

https://www.arrl.org/shop/Grounding-and-Bonding-for-the-Radio-Amateur

and also... (free)...

https://forums.qrz.com/index.php?forums/antennas-feedlines-towers-rotors.33/  (see the first three pinned threads - "Grounding Dos and Don'ts"

Have fun, stay safe,

Brian - K6BRN
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W9IQ
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Posts: 3531




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« Reply #6 on: April 13, 2019, 04:33:00 AM »

Bill,

The reduction in voltage indicates that bonding the two ground systems would be beneficial.

The purpose of bonding all ground rods is to maintain the safety ground system at near equipotential levels. This becomes particularly important in the event of a neutral connection failure that would allow substantial current to flow in the safety ground system. So under your existing conditions, the difference in voltage is small but with substantial current on the safety ground, the voltage difference could become substantial.

In the US, the often cited NEC requires that all ground rods be bonded together with at least 6 gauge wire - larger gauge or multiple #6 is even better. I also recommend that you consider using an exothermic connection, such as Cadweld, to form trouble free connections.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
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