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Discussion Starter · #1 ·
Hi;
I may need to install a second ground electrode. When I make the bond between existing and new, can I use an approved clamp (split bolt) to make the connection at the existing electrode, or do I need to provide one continuous conductor through both electrodes from the disconnect panel?

I have read over NEC 250.64 through 250.68 and am confused on this matter.

Thanks

FW
 

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Each GEC has to be continuous from the first point of disconnect to the electrode.
 

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Hi;
I may need to install a second ground electrode. When I make the bond between existing and new, can I use an approved clamp (split bolt) to make the connection at the existing electrode, or do I need to provide one continuous conductor through both electrodes from the disconnect panel?

I have read over NEC 250.64 through 250.68 and am confused on this matter.

Thanks

FW
Don't use a split bolt use an acorn clamp if these electrodes are rods. GEC needs to be continuous to the first electrode after that you can use bonding jumpers to the others.

 
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Discussion Starter · #4 ·
Thanks guys;
That's the impression I got when I read the NEC.
After I posted this, I had a thought;
By adding a GE, I will be modifying the electrical system, and therefore require a permit and an inspection for the work. In addition, because I will be pounding a 5/8" rod 8ft into the ground, I will need utilities to be marked off.

The purpose for this second GE was to improve RF conditions for my Amateur radio equipment.
I think now that I will simply run my antenna/radio grounding system to the existing GE instead of installing a second one. The only difference is that I will need about 20-30ft more coax cable.

Let me ask another question:
What would be the result of a higher than acceptable impedance between GC/GE and the earth?

FW
 

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The maximum number of ground rods needed is two at each building even if you do not achieve the impedance threshold (25 ohms or less) with the earth.

A grounding electrode conductor must run non-stop from the panel with the main disconnect to at least one grounding electrode. Additional electrodes' GECs may be tied onto that. But if a grounding electrode needs a fatter GEC, such as #4 from a water pipe for a service with #1/0 to #3/0 service conductors , that one has to run non-stop to the panel.
 

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Discussion Starter · #6 · (Edited)
The maximum number of ground rods needed is two at each building even if you do not achieve the impedance threshold (25 ohms or less) with the earth.

A grounding electrode conductor must run non-stop from the panel with the main disconnect to at least one grounding electrode. Additional electrodes' GECs may be tied onto that. But if a grounding electrode needs a fatter GEC, such as #4 from a water pipe for a service with #1/0 to #3/0 service conductors , that one has to run non-stop to the panel.
OK. So I could install another GE and connect it with another length of #6 (the size used from the panel to the existing GE). (Stubbie said that in his reply, but for some reason I failed to register it)

The whole purpose of my query is that I am trying to figure out what is causing the interference on my VHF Ham radio.
Further testing this morning is showing some evidence that I have a poor connection between my antenna and the earth, which is made at the GE to which the electric service is connected.
By installing a 2nd GE, I may improve my RF situation, and at the same time reduce the vulnerability of our electrical system from lightning.
I also have a lightning arrestor on the coax transmission line from the antenna, but it is currently located up on the mast; it needs to be moved to the GE to which it is now connected through a 40ft length of #4 THHN.

In addition, it may be prudent to check the existing connection at the GE, and possibly replace the acorn clamp there. It feels as though there is a slight amount of movement between the conductor and the electrode, but the wire will not pull out. For electrical, this may not present a problem, but for RF it could. A poor connection can itself even create certain types of interference.
Of course, I also need to check the connections on the antenna/mast.

FW
 

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Discussion Starter · #7 ·
Another question:
NEC 2008 260.64(B) Securing and protection against physical damage.

What is the difference in the requirements between #4 and larger, and #6?
It appears that all GEC #6 and larger must be protected against physical damage. But why is #6 specifically allowed to be run along building structure?
Can I not run #4 copper GEC along building structure if it is not subject to physical damage?
I do understand that GEC smaller than #6 must be run in conduit.

I guess I should get a copy of the NEC interpretive guide. Trying to make sense of the code itself is like reading legal documentation.

Thanks

FW
 

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Another question:
NEC 2008 260.64(B) Securing and protection against physical damage.

What is the difference in the requirements between #4 and larger, and #6?
It appears that all GEC #6 and larger must be protected against physical damage. But why is #6 specifically allowed to be run along building structure?
Can I not run #4 copper GEC along building structure if it is not subject to physical damage?
I do understand that GEC smaller than #6 must be run in conduit.

I guess I should get a copy of the NEC interpretive guide. Trying to make sense of the code itself is like reading legal documentation.

Thanks

FW
The largest required GEC is a #4 in the NEC. #6 is smaller than #4.

I don't think adding more grounding is going to help your reception. I am not radio expert, but I hear this all the time.
In the electrical trade we use electrodes and their conductors for one reason and one reason only. Lightning.
 

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Discussion Starter · #9 ·
The largest required GEC is a #4 in the NEC. #6 is smaller than #4.

I don't think adding more grounding is going to help your reception. I am not radio expert, but I hear this all the time.
In the electrical trade we use electrodes and their conductors for one reason and one reason only. Lightning.
I was just curious as to why the section specifically stated that #6 wire can be run along a building without conduit (so long as there is no risk of physical damage), but for #4 and larger a different statement is made (similar it seems, but not what it said specifically for #6).

For my Ham radio station (which is only a 2m HT connected to an outdoor antenna on the peak of the house), I am not expecting better reception for better grounding. I am troubleshooting interference from an AM broadcast station (I just found which one a few minutes ago) under a specific condition.
This issue really belongs in a Ham radio board, and I have posted it there.

FW
 

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Adding another grounding electrode to your electrical system will do nothing useful for your VHF transceiver. Read up on RF theory and antenna design/installation. The equipment grounding conductor and electrical service's grounding electrode are basically incapable of being useful for a VHF transmitter. Why? Consider the length of the grounding conductor between the transceiver and the ground rod. It is many wavelengths long, follows a twisting path, and is completely non-impedance-controlled. To a 100MHz-plus signal it is an open circuit and a long-wire antenna, not a ground connection. If you need a grounding connection for a VHF antenna, the grounding connection must be AT the antenna, and carefully designed to RF considerations. A grounded antenna mast is a good example - it is straight, vertical, relatively short, and has low impedance to the earth. Even taking advantage of a grounded mast requires careful planing though, since the portion of the mast near the antenna functions as part of the antenna itself and affects the impedance and radiation pattern. For VHF, the better solution is to use a balanced antenna, with a balun at the antenna to convert to a coax feed from the transceiver. Assuming you do the impedance matching properly, no grounding connection is actually necessary since the system is completely balanced (there is no net flow of charge into or out of the antenna/feedline/transceiver system). This is how all properly designed and tuned transmitter installations work, with the exception of HF systems that use the earth as a charge reservoir for a single-ended antenna because the wavelengths are too long to make a dipole practical. The emphasis on grounding in some amateur radio literature (and tradition) comes from the olden days of tube-powered HF gear, when it really did matter because there was RF current flow through a station's grounding system in normal operation. Modern equipment on shorter wavelengths has rendered that obsolete, and it remains a source of confusion for hams who try to troubleshoot from the old school methods without actually learning the RF theory that describes how their stations really works.

In short: It's probably the antenna system, and definitely not the grounding system.

DE KC0LLX
 
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Discussion Starter · #11 ·
Adding another grounding electrode to your electrical system will do nothing useful for your VHF transceiver. Read up on RF theory and antenna design/installation. The equipment grounding conductor and electrical service's grounding electrode are basically incapable of being useful for a VHF transmitter. Why? Consider the length of the grounding conductor between the transceiver and the ground rod. It is many wavelengths long, follows a twisting path, and is completely non-impedance-controlled. To a 100MHz-plus signal it is an open circuit and a long-wire antenna, not a ground connection. If you need a grounding connection for a VHF antenna, the grounding connection must be AT the antenna, and carefully designed to RF considerations. A grounded antenna mast is a good example - it is straight, vertical, relatively short, and has low impedance to the earth. Even taking advantage of a grounded mast requires careful planing though, since the portion of the mast near the antenna functions as part of the antenna itself and affects the impedance and radiation pattern. For VHF, the better solution is to use a balanced antenna, with a balun at the antenna to convert to a coax feed from the transceiver. Assuming you do the impedance matching properly, no grounding connection is actually necessary since the system is completely balanced (there is no net flow of charge into or out of the antenna/feedline/transceiver system). This is how all properly designed and tuned transmitter installations work, with the exception of HF systems that use the earth as a charge reservoir for a single-ended antenna because the wavelengths are too long to make a dipole practical. The emphasis on grounding in some amateur radio literature (and tradition) comes from the olden days of tube-powered HF gear, when it really did matter because there was RF current flow through a station's grounding system in normal operation. Modern equipment on shorter wavelengths has rendered that obsolete, and it remains a source of confusion for hams who try to troubleshoot from the old school methods without actually learning the RF theory that describes how their stations really works.

In short: It's probably the antenna system, and definitely not the grounding system.

DE KC0LLX
Thanks for the very helpful reply. I will copy and paste it into my journal where I keep my progress (or lack of) on my 2m project.
I wish that I would have remained "radio active" since my HF days, but I lost interest in radio, and in electronics and RF in general, although was employed in the field (electronics, not RF) for many years.
I still have the thinking of a 20 something year old when it comes to a lot of this, but I find that re-learning everything I knew when I was experimenting on HF is much more difficult now.

What you said is logical in my mind. I sometimes clutch at straws (or ghosts) when I have a problem I cannot solve.

I am trying to study up on RF theory, but having trouble finding the right books. I thought about buying the 2013 RA handbook from ARRL, but maybe I can get it (or last year's) from my local library and see how useful it would be before buying my own copy.

At this point, my interest in grounding the antenna is mainly for lightning protection. Every article I have read on the ICE #302 says that it should be installed as close to the GE as possible, so I think I should relocate mine. That would at least reduce the possibility that a lightning hit will bring high currents into the house on the coax.

As for RF grounding, I still remember the laws governing XL, XC, R, and Z, so I understand that a long length of wire is a very high resistance at 144Mhz.

Balanced antenna for VHF? I don't think I've seen one recently.
Too bad I don't have an HF rig set up, or I would try to contact you.
I don't want to cross post, but we should get together in one of the Ham forums to discuss this further.

If you have any suggestions on reading to better my education in RF principles, please share.

Thanks

KE2KB
 
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