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Scanner / Receiver Antennas For discussion of any type of receiving antenna used by a scanner or receiver base, mobile or handheld.

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Old 05-29-2009, 4:53 PM
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Default Connecting multiple ground rods

I recently moved into a new house and I'm getting ready to start my antenna projects. The builder's electrician installed two copper ground rods which are about 10 feet apart and bonded together. The rods are located near the electric service entrance (meter) and there's a ground wire that runs from the meter base to the rods. The telephone and cable TV feeds are tied into the ground rods, too.

Unfortunately, all of this is on the opposite side of the house from where I want to put my radios (may have been bad planning on my part, but it is what it is). I have thought about installing another ground rod near the future radio room. However, good grounding practice tells me that all of the ground rods need to be bonded together.

It would be possible, but not entirely practical, to run a ground wire around the back of the house from the new ground rod to the existing ground rods. On the other hand, I think I remember someone on here mentioning that they had a similar situation and ran the ground wire through the basement or crawl space from one side of the house to the other. Is this a legitimate answer? Does it meet code?

Thanks for your input.
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Old 05-29-2009, 5:22 PM
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My educated guess would be to install a new ground rod, on the side of the house where you intend to locate your radio room. My suggestion, is to isolate a new, proper grounding rod, deep into the soil, on the side closest to that room. The reason I suggest this, is because if you tied all of the grounds together, you are also tying them into the antenna which may act as a lightning attractor, and it may increase or allow a direct hit to back feed into the house TV or Phone system, or Cable TV system. An isolated ground connected to an outdoor mast and antenna sounds like the correct way to go, but I'm not an electrician or electrical contractor, so my suggestion may not be correct. I would hate to see ya loose your phone, cable, TV and other stuff by incorporating an antenna on a tall mast connected together on one shared ground rod... Shared also means they all share the possibility of damage if the antenna is ever hit by lightning. Why introduce those elements to an antenna system, when the antenna acts like a lightning rod by itself attracting lightning. Separation is probably the way to go.

Regarding running the ground wire thru the basement , under the house to get from one side to the other is also probably a poor idea. The best protection during a direct lightning hit, would be to divert the charge down to a ground rod in the shortest possible distance to dispurse it into ground. why bring that hazzard into the house and then out again , especially over a longer attatched ground wire to make the connections... I would buy a super long ground rod, and get it down into the ground as directed, and then attatch a super duti heavy guage ground wire between the mast and the ground rod, and if possible, maybe even attatch a second ground wire from the mast to a metal water supply pipe for additional grounding. Good luck to you.
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Old 05-29-2009, 5:57 PM
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I guess that your educated guess may not have much guess in it. Those that work in the electrical
field and the telecommunications field should be familiar with the grounding requirements of the
"National Electrical Code", guidelines from the "NFPA' (National Fire Protection Agency) and what
many call the grounding bible from Motorola, the R56 standard. Plus it wouldn't hurt to check
with your home insurance company.

What this all means is that you want to keep current from flowing between different pieces of
metal, electrical wiring and ground systems during a lightning strike. The best way to reduce and
prevent damage is to have all the different pieces bonded together with a low impedance ground
system. This means no isolated ground rods, as low of a ground resistance on your ground
system, bonding of everything that should be at ground potential together and so on.

if you can take the time, look over a cellular tower site. You might find a few things there that
you never thought of. like the chain link fence around the site has a number of ground wires
attached to it. The gate where you drive into the yard has wire flex jumpers from the support
pipe to the movable gate. the tower has ground wires from each leg, the coax cables are
each individually grounded, the ice bridge where the coax cables go from the tower to the
equipment shelter has a ground wire on each support pipe. the ice bridge is not connected to
either the tower or the shelter. It is self supporting. You can't see the inside of the shelter, but
every metal item inside is bonded to the ground system. Even the door frame and the metal
air conditioner frames are grounded.

Bottom line here is to keep any current flow from occuring durring the strike. If you have 2 different
ground rods on different sides of the house, there is bound to be current flow between them. The
best thing you could do is to run a solid number 2 tinned copper wire from one ground rod to the
other. Bury this wire at least 30 inches below the surface and add additional ground rods along the
run. The rods should be spaced no closer than twice their length. In other words, if you use 8 foot
ground rods, space them at least 16 feet apart. Make no sharp bends in the wire.

There are a number of good documents available here on the web that go into details of all this.
It wouldn't hurt to try a search on the subject. Been in this field of radio site engineering and
construction for better than 40 years now. I can say that grounding a tower site correctly,
the tower can take a direct strike and everything will keep on ticking like nothing happened. Have
seen a number of towers take a strike, steam a little in the rain and the radio equipment just
keeps on doing it's thing.

Jim



Quote:
Originally Posted by khoelldobler View Post
My educated guess would be to install a new ground rod, on the side of the house where you intend to locate your radio room. My suggestion, is to isolate a new, proper grounding rod, deep into the soil, on the side closest to that room. The reason I suggest this, is because if you tied all of the grounds together, you are also tying them into the antenna which may act as a lightning attractor, and it may increase or allow a direct hit to back feed into the house TV or Phone system, or Cable TV system. An isolated ground connected to an outdoor mast and antenna sounds like the correct way to go, but I'm not an electrician or electrical contractor, so my suggestion may not be correct. I would hate to see ya loose your phone, cable, TV and other stuff by incorporating an antenna on a tall mast connected together on one shared ground rod... Shared also means they all share the possibility of damage if the antenna is ever hit by lightning. Why introduce those elements to an antenna system, when the antenna acts like a lightning rod by itself attracting lightning. Separation is probably the way to go.

Regarding running the ground wire thru the basement , under the house to get from one side to the other is also probably a poor idea. The best protection during a direct lightning hit, would be to divert the charge down to a ground rod in the shortest possible distance to dispurse it into ground. why bring that hazzard into the house and then out again , especially over a longer attatched ground wire to make the connections... I would buy a super long ground rod, and get it down into the ground as directed, and then attatch a super duti heavy guage ground wire between the mast and the ground rod, and if possible, maybe even attatch a second ground wire from the mast to a metal water supply pipe for additional grounding. Good luck to you.
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Old 05-31-2009, 9:36 AM
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Quote:
Originally Posted by jim202 View Post
The best way to reduce and prevent damage is to have all the different pieces bonded together with a low impedance ground system.
It's always been my understanding of the NEC that all grounds in a structure should be bonded together to avoid any single ground point being at a different potential from the others. That's why I mentioned connecting the grounds rods even though they'll be on different sides of the house. The problem is how to route that ground wire. I believe someone on here mentioned running the ground wire through their basement/crawl space. I raised an eyebrow when I read it and wondered what others thought.
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Old 05-31-2009, 11:05 AM
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Like everyone agrees they should be bonded together, but I would not go thru the interior of the house; and the bad thing is that # 2 copper is expensive, although it is coming down. Maybe the best compromise would be to use # 6 bare copper any bury it between the grounding electrode system and your antenna location. A lot of inspectors are wanting 2 ground rods lately to get below 25 Ohms as required by the code. (They must be bonded together and at least 6 feet apart) If you also put a ground rod at your antenna location it would not violate code if everything is bonded together. The code does not require a "Made electrode" ground conductor to be larger than #6 copper.
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Old 05-31-2009, 11:10 AM
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If your yard will permit and if you can afford it, make a buried ground ring completely around the house using large bare copper wire (00 or larger) and bond that to maybe 8 or more rods spaced around the perimeter. This is how many commercial broadcast and communications sites are built and the building I work in originally had 75 rods around the perimeter and 500MCM copper wire 4ft below ground. Over the last 10yrs we have probably added another 50 or more rods as new antennas go in.
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Old 05-31-2009, 2:19 PM
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Quote:
Originally Posted by prcguy View Post
If your yard will permit and if you can afford it, make a buried ground ring completely around the house using large bare copper wire (00 or larger) and bond that to maybe 8 or more rods spaced around the perimeter. This is how many commercial broadcast and communications sites are built and the building I work in originally had 75 rods around the perimeter and 500MCM copper wire 4ft below ground. Over the last 10yrs we have probably added another 50 or more rods as new antennas go in.
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