Rooftop Antenna Grounding

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ajm511

PE (Electrical)
Location
Bay Area
Occupation
Engineer
Hello,

I am curious on how a privately-owned rooftop antenna should be grounded. I know 810.21 requires that the antenna to be connected to the grounding electrode system in a few ways:
  1. via the intersystem bonding termination
  2. or directly to the grounding electrode system. Whether it's a water pipe (Within 5'), building structure, or the grounding electrode conductor.
In the case of a concrete building with no steel structure, are any of these acceptable to ground the antenna mast?
  1. Bond to exposed rebar if that rebar is continuous to the rebar at the ground level that is considered a grounding electrode conductor?
  2. Bond to a telecom bonding busbar inside a telecom room closer to roof level? Is the telecom bonding system considered an intersystem bonding termination if it eventually connects back to the grounding electrode system?
  3. Or does a dedicated conductor need to be run all the way down to the grounding electrode conductor or water pipe entrance?

Thank you
 
Just my opinion...

1) is questionable (how you gonna prove the rebar is continuous?)
2) seems okay, like you can argue the telcom room busbar is an extension of the IBT
3) is the bullet proof solution to avoid an argument with an inspector. You should go to the IBT if there is one, instead of the things you mentioned.
 
In a somewhat related story...

When I was a young lad in college in Baton Rouge I used to park out by the campus lakes with my girlfriend and listen to the AM radio (yes, it was that long ago) late at night, and our favorite station to listen to was KAAY in Little Rock. It was Clyde Clifford's Beaker Street "underground radio" show, if anyone remembers.

Reception was spotty because of the distance but it was usually listenable. Anyway, one night someone had broken off the antenna on my car and I could not bring the station in. I had some bare copper wire in my trunk, so I tried stringing a short length of wire from the antenna stump to a tire iron driven into the ground. KAAY came in like gangbusters as if it were merely a mile away.
 
ggunn said:
In a somewhat related story...

When I was a young lad in college in Baton Rouge I used to park out by the campus lakes with my girlfriend and listen to the AM radio (yes, it was that long ago) late at night, and our favorite station to listen to was KAAY in Little Rock. It was Clyde Clifford's Beaker Street "underground radio" show, if anyone remembers.

Reception was spotty because of the distance but it was usually listenable. Anyway, one night someone had broken off the antenna on my car and I could not bring the station in. I had some bare copper wire in my trunk, so I tried stringing a short length of wire from the antenna stump to a tire iron driven into the ground. KAAY came in like gangbusters as if it were merely a mile away.
Click to expand...
I remember. I listened to it...with a good radio setup it was listenable a few hundred miles north in Council Bluffs IA at night.

I have a tiny little beat-up Radio Shack pocket radio. I can lie in bed in my small town north of Des Moines and hear WWL New Orleans most nights without a problem (yesterday was their 100th anniversary). I listened to their Katrina coverage that way.

One of my clients purchased a FM radio station whose transmit antenna is atop a derelict three-story concrete-and-steel building. The antenna is crudely grounded to rebar...each perimeter support column has a rebar curled into an eyelet at roof level. We're moving away to a real tower soon, and I'll be much happier when we do.
 
jaggedben said:
Just my opinion...

1) is questionable (how you gonna prove the rebar is continuous?)
2) seems okay, like you can argue the telcom room busbar is an extension of the IBT
3) is the bullet proof solution to avoid an argument with an inspector. You should go to the IBT if there is one, instead of the things you mentioned.
Click to expand...
1) You could verify with the structural engineer and electrical engineer that the rebar system connects to the electrode system. If that is the case, would this be allowed?
2) I'm concerned that a lightning strike or nearby strike could reach and damage network equipment along the telecom bonding system. I really don't know if that's a true concern or not.
3) Agreed, this would never get flagged by an inspector but has cost implications for large buildings.
 
grich said:
I remember. I listened to it...with a good radio setup it was listenable a few hundred miles north in Council Bluffs IA at night.
Click to expand...
Wow, another old frint like me. Clyde played songs that I have never heard on the radio before or since, like:
The Legend of the USS Titanic - Jaime Brockett
Hunting Tigers Down in India (YAH!) - The Bonzo Dog Band
Cindy's Crying - Barbara Raney

His show was in stark contrast to the Top 40 AM radio I heard everywhere else at the time, and FM radio was still only in California and other places remote from south Louisiana where I was living at the time. It was my first exposure to many bands I had never heard of.
 
ggunn said:
Wow, another old frint like me. Clyde played songs that I have never heard on the radio before or since, like:
The Legend of the USS Titanic - Jaime Brockett
Hunting Tigers Down in India (YAH!) - The Bonzo Dog Band
Cindy's Crying - Barbara Raney

His show was in stark contrast to the Top 40 AM radio I heard everywhere else at the time, and FM radio was still only in California and other places remote from south Louisiana where I was living at the time. It was my first exposure to many bands I had never heard of.
Click to expand...
As much as I'm enjoying the back and forth, any input on the bonding point for antennas on a concrete building? :)
 
ggunn said:
In a somewhat related story...

When I was a young lad in college in Baton Rouge I used to park out by the campus lakes with my girlfriend and listen to the AM radio (yes, it was that long ago) late at night, and our favorite station to listen to was KAAY in Little Rock. It was Clyde Clifford's Beaker Street "underground radio" show, if anyone remembers.

Reception was spotty because of the distance but it was usually listenable. Anyway, one night someone had broken off the antenna on my car and I could not bring the station in. I had some bare copper wire in my trunk, so I tried stringing a short length of wire from the antenna stump to a tire iron driven into the ground. KAAY came in like gangbusters as if it were merely a mile away.
Click to expand...
In effect, you made the antenna stub the ground, and the insulated body of the car the antenna. Very good for AM radio frequencies.
 
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