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Author Topic: Equipment grounding confusion  (Read 511 times)

KA1JNK

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Equipment grounding confusion
« on: December 15, 2020, 04:05:14 PM »

I am setting up my station and have a grounding buss behind the desk that is bonded to my house ground. My antenna coax will be grounded via a lightning arrestor to ground rods outside which are also bonded to my house ground.

So today I was looking at my power supply, QCX+ radio, and AT considering how I was going to connect them to the buss bar.Then, for the heck of it, I took my ohm meter and tested the PS chassis to the ground buss and, of course, had continuity because the PS has a 3 pronged plug that goes to house ground.
Then I thought, the coax shield will be grounded to the ground system before it enters the house so when it is connected to the AT and radio they will be grounded to the system as well. If everything is already tied into the ground system, why do I need to connect their chassis to the buss bar?
David
KA1JNK




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W0WCA

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Re: Equipment grounding confusion
« Reply #1 on: December 15, 2020, 05:54:15 PM »

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SWMAN

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Re: Equipment grounding confusion
« Reply #2 on: December 15, 2020, 06:49:48 PM »

WCA,  that is some very good ground loop info, I learned a few things from it, hopefully the OP did also. Thanks
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KA1JNK

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Re: Equipment grounding confusion
« Reply #3 on: December 16, 2020, 04:51:23 AM »

I offer the following:
https://en.wikipedia.org/wiki/Ground_loop_%28electricity%29
Thank you, that helped a lot.
In the explanation it said...A ground loop is caused by the interconnection of electrical equipment that results in there being multiple paths to ground, so a closed conductive loop is formed. A common example is two pieces of electrical equipment, A and B, each connected to a utility outlet by a 3 conductor cable and plug, containing a protective ground conductor, in accordance with normal safety regulations and practice. This only becomes a problem when one or more signal cables are then connected between A and B, to pass data or audio signals from one to the other. The shield of the data cable is typically connected to the grounded equipment chassis of both A and B, forming a closed loop with the ground conductors of the power cords, which are connected through the building utility ground wire. This is the ground loop.

So, if I understand this correctly, in my current  situation (pun intended) where I have a PS with a 3 conductor cable plugged into AC and a QRP rig and AT connected directly to the PS and not to AC, there would be no need to attach anything to the ground buss because there is only one piece of equipment connected to the utility outlet, or am I missing something?
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W9IQ

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Re: Equipment grounding confusion
« Reply #4 on: December 16, 2020, 05:53:27 AM »

You may wish to open your power supply to see what it would take to disconnect the AC safety ground from the minus connection on the low voltage side. Often there is a simple jumper for this task - other times it is a convoluted route through circuit boards and metal standoffs.

You will still have a ground loop as it is unavoidable but it will be outside of the shack so it doesn't have as great of a potential to affect your station.

- Glenn W9IQ

« Last Edit: December 16, 2020, 06:06:30 AM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

KD6VXI

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Re: Equipment grounding confusion
« Reply #5 on: December 16, 2020, 08:28:22 AM »

There are some professional engineers that take offense at the term "Ground Loop".

If everything is bonded correctly, using shiny metal connections (which I then apply some type of moisture barrier to, even Vaseline would work in some cases) then their can be no "loop".

What you are afraid of has actually been termed "The Pin 1 Problem".  Jim Brown, Ward Silver, etc have all written about this issue.  And it's not so easy to fix / is an easy fix depending on your familiarity with your equipment.

To Wit:  The green wire inside most iron based Astron and Tripp Lite power supplies is connected to a painted surface!  That is NOT a good bond! 

Also, as Glenn said, disconnect your (-) lead of the power supply from the AC equipment ground. 

This is also why One Shot style exothermic welds are required in any type of grounding system that has any appreciable current capabilities.  You don't want a couple ohms on each ground rod creating issues if it has to sink the current of a lightening stroke or a fault to ground.

--Shane
KD6VXI
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KF5LJW

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Re: Equipment grounding confusion
« Reply #6 on: December 16, 2020, 08:39:22 AM »

OP go read this website.
http://www.repeater-builder.com/tech-info/bonding/amateur-radio-bonding.html   
It will answer all your questions. You are in a Ground Loop.
There are some professional engineers that take offense at the term "Ground Loop".

If everything is bonded correctly, using shiny metal connections (which I then apply some type of moisture barrier to, even Vaseline would work in some cases) then their can be no "loop".
KD6VXI
Not this PE because he knows better. To believe that completely ignores basic fundamentals and requires you to believe in myths. Myth #2

2. Wires have low impedance - and, therefore, conducts RF current effectively and efficiently. While understandable, is fundamentally incorrect. Requires you to ignore Ohm's law and the AC impedances of Single-Wire Circuits. To be an effective and efficient circuit conductor requires low impedance. A Single-Wire Circuit only has low impedance at DC and 60-Hz power frequencies. It is physically impossible to use single-wire conductors like grounds for anything other than power frequencies.

Wire of any length or gauge has both DC Resistance and AC Impedance. The resistance and impedance of a wire are directly proportional to its length. The DC resistance of a ten feet length of #12 AWG copper wire is about 0.015 Ohms, making an excellent circuit conductor. At 60-Hz is fractionally higher at 0.02 Ohms, making it a good conductor at 60 Hz.

The inductance of any wire is nearly independent of its diameter (gauge). Inductance is directly proportional to its length and increases with any bends or loops. The same piece of #12 AWG 10-feet of copper wire has an impedance of 30-Ohms at 1 MHz making it unusable as a circuit conductor. Increase the gauge to 750 MCM, the size of your wrist, and the impedance drops slightly to 25 Ohms. At 25 MHz it becomes essentially an open circuit. Apply Ohm's law. Myth busted.

Fact: All ground wires are for safety and 0-Volt reference point. It is not physically possible for equipment grounds and ground conductors to do anything else. Ground wires are Single-Wire Circuits, where the conductor does not have an equal and opposite associated circuit conductor to cancel out the mutual inductance of both circuit conductors. When two or more circuit conductors coupled closely together form a transmission line. Do not limit your thinking a transmission line is just your coax or ladder line. Audio and telephone circuits use Tip and Ring. Even AC power circuits in your home use a transmission line called a Branch Circuit. For a circuit conductor to be effective and efficient requires impedance to be milli-ohms, not 10's 100's, or 1000's of ohms.
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