Ground electrode conductor (GEC) and radio tower ground

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Geber

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Location
Vermont
Occupation
PE, retired electronics engineer
An existing commercial building has a 6 AWG GEC running from one of the two side-by-side service panels to a single ground rod. A radio tower will be re-erected; it has three ground rods which form a triangle; sides of triangle are about 18 inches long. The most nearly applicable article seems to be 810.51 and 801.58. Some of the radios are amateur radios, and the public safety radios are electrically identical to amateur radios. 810.51 leads to 801.15, which leads to 801.21(J), which requires the radio ground to power grounding electrode system to be connected with 6 AWG.

If I run the connection directly between the power and radio ground rod, does that mean that the power GEC is no longer the sole connection to the building ground rod, and thus require the 6 AWG GEC be replaced with a GEC sized according to table 250.66 (in the case of this building, it would be 1/0)? Would it be OK to avoid this size increase by running 6 AWG from the service panel to the radio ground?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
That is a question I asked at our NC meeting and was told it was compliant. We often run from one rod to another so why would this be different.

BTW if there were a concrete footer with rebar I would tie to that rather than rods. You could do both but then you would have to change the wire to #4.

Is there no panel at the tower?
 

Geber

Member
Location
Vermont
Occupation
PE, retired electronics engineer
No panel at tower

No panel at tower

There is no panel at the tower, in part because the radio room is on the second floor, so the cables will leave the tower about 12 feet above grade. I expect each cable shield will be attached to the tower with a suitable device at the point where the antenna is mounted and again at the point of departure from the tower. Some kind of single point ground panel with static discharge devices will be mounted in the radio room.
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
Are you trying to determine code minimum, or an effective design?

By the sounds of things you are in an emergency communications center. Code minimum shouldn't even be a consideration.

The questions you need to ask are:

1) Is my design suitable to provide a path back to the source for an AC fault?

2) Will my design act as an antenna and cause the radios to be interfered with from nearby strong signals?

3) Will my design contribute to any undesirable interaction between radios?

4) Is my design stout enough to handle lightning strikes?

5) Does my design keep the radio operators out of harm's way during an electrical storm?

6) Does my design cause or contribute to interference to other devices, like computers or intercoms?

If you can't answer these questions, and prove the answers, you should not be involved with designing any part of the grounding system. A professional hired by the municipality the radios belong to should be utilized and the person should be bonded and insured and have a track record to look at.
 
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K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
I have some experience with this issue.

Our back up 911 center has amateur radios in it. I help put some of it together. I am an Amateur Extra, referred to by lay people as an Extra Class amateur radio operator.

The City's comm tech and chief radio installer is an Extra.

The City's electrical inspector is an Extra.

The cop that is the Emergency Communication Coordinator is an Extra.

Our contact at the company that sells the commercial gear is a Technician Class operator.

We still have all our designs engineered, but maintain the gear ourselves, with the exception of climbing 325 feet to our repeater antennas.
 

Geber

Member
Location
Vermont
Occupation
PE, retired electronics engineer
Just curious.....

What brand and model radios are they?

At present we have some older radios that belong to the local radio club. There is an ICOM 735 for HF, an old Kenwood ham FM rig for 2 m, another old Kenwood ham FM rig for 70 cm, and two old mobile commercial radios, one for 47 MHz and one for 155 MHz. One of these is new enough to be narrow banded when the time comes, the other will have to be reprogrammed for 6 m or retired. With luck, a working radio room will attract some more modern donations.
 

Geber

Member
Location
Vermont
Occupation
PE, retired electronics engineer
Ground electrode conductor (GEC) and radio tower ground

I've interspersed my comments with your questions.

By the sounds of things you are in an emergency communications center. Code minimum shouldn't even be a consideration.

It's a Red Cross building; communications are normally by phone and internet. The radio room is a best-effort backup, not a required service.​

The questions you need to ask are:

1) Is my design suitable to provide a path back to the source for an AC fault?
This one is relatively easy to figure out for an Amateur Extra (WY2Y) with 20+ years electronics experience, dealing with currents up to 1 kA, and a PE license.​

2) Will my design act as an antenna and cause the radios to be interfered with from nearby strong signals?
The radio room operated well in a similar configuration before a major storm blew the tower down, so I'm not anticipating a problem.​

3) Will my design contribute to any undesirable interaction between radios?
Again, it worked well before, but single point ground and testing are called for.​

4) Is my design stout enough to handle lightning strikes?
A design that reliably protects against lightning with operators at the controls is not financially feasible, so the station will have to stop operating during electrical storms. Yes, this is a significant limitation. I believe the most affordable way to overcome this limitation would be a remotely controlled sacrificial radio controlled with a wireless laptop.​
5) Does my design keep the radio operators out of harm's way during an electrical storm?

6) Does my design cause or contribute to interference to other devices, like computers or intercoms?
This will require testing since new phones and computers have been installed since the radios were last operated.​

If you can't answer these questions, and prove the answers, you should not be involved with designing any part of the grounding system. A professional hired by the municipality the radios belong to should be utilized and the person should be bonded and insured and have a track record to look at.

The best-effort status of this radio room allows us to test and just eliminate radios that cause problems that we can't resolve. But I am seeking out professionals with more grounding experience. I think the area most in need of professional attention is the structural aspects of the tower.

It is useful to get ideas that allow one to estimate costs; if the costs are too high we'll just have to say, "hey guys, take your radios home, this won't work."​
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
Understood, and fine business.

We have a room at our Red Cross building, I worked on that installation as well.

Your first description made it sound like a public safety installation, or PSAP, and as such would require stricter standards and documentation at the municipality's expense.

Our ARC station is on the second floor and the tower is on the roof. All coax is protected by PolyPhaser arrestors at the point they enter the building. The grounding window is bonded to the building steel.

Are you familiar with PolyPhaser's web site and their tech support area? They changed the link or else I would have it here for you.

Another good source for grounding issues is AVO. This book is great for determining the integrity of a grounding system. http://www.megger.com/us/story/Index.php?ID=146

As for the questions, they were posed with the assumption that you were a regular EC with no experience in communication systems. It looks like you have it covered.

I own a 735 and think it is a great radio. We set it side by side with a new 718 and it made the 718 look like a toy.

We got 8500 bucks from the Department of Homeland Security to put up the tower and antennas at the ARC. One of our RACES members wrote for a grant and got it.

We never have used HF at the ARC. Not all ARC's have HF, but some do. I have seen them with big tri-banders. Also, the comm vans are equipped with HF. They have Kenwood 2000's in them and a tri-band antenna that fits on the boom.

Most emergency comms are done on 2 meter FM. Digital modes are great, but with HIPPA we no longer have the need to transmit lists of names.

Back to grounding. Try to find some #2 Solid Bare Tinned Copper wire. The phone company uses it for their installations and you may be able to get a roll end for what they paid for it. It's probably over 2 bucks a foot now.

Good luck. Our ARC call is W8NVY. The liaison between the Red Cross and amateur radio is an Extra that was a student in my very first radio class. You can read more about W8NVY on QRZ.com.

73!
 

Geber

Member
Location
Vermont
Occupation
PE, retired electronics engineer
Useful sites, frequency use

Useful sites, frequency use

...Are you familiar with PolyPhaser's web site and their tech support area? They changed the link or else I would have it here for you.

Another good source for grounding issues is AVO. This book is great for determining the integrity of a grounding system. http://www.megger.com/us/story/Index.php?ID=146...

We never have used HF at the ARC. Not all ARC's have HF, but some do. I have seen them with big tri-banders. Also, the comm vans are equipped with HF. They have Kenwood 2000's in them and a tri-band antenna that fits on the boom.

Most emergency comms are done on 2 meter FM. Digital modes are great, but with HIPPA we no longer have the need to transmit lists of names.

I've looked pretty carefully at the PolyPhaser site, as well as the Alpha-Delta site, the DX Engineering site, and the Galvan site.

Most of our local (small) disaster comms are done on 2 m and 70 cm, but Vermont Emergency Management is equipped with HF and likes to use 80 and 40 m.
 
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