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Author Topic: Feed-line entrance and grounding / protection.  (Read 1420 times)
KB8BAB
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Posts: 101




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« on: June 18, 2012, 10:37:52 AM »

Hello all,

Just got the tower up, still have a few things to do, but have some questions regarding feed-line entrance.

I currently have the tower grounded, but still need to run a line to the mains ground from the house, this will make for the "common" ground requirements.

I'm in the process of ordering 2 Alpha Delta ATT3G50 arrestors...but where to mount them?

- Can these be mounted outside? Directly on the tower? Or should they be mounted elsewhere? (In an enclosure?) I'm open to suggestions...

- Feed line entrance... what are you guys using? I can go through the wall if need be.

Thanks...Bart
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NA7U
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Posts: 72


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« Reply #1 on: June 18, 2012, 03:42:38 PM »

Exactly where is that second ground line to the "mains ground" running from? The tower?

I'd mount the arrestors on the outside of the house as close as possible to your station ground, which also should be outside and to which everything should be grounded. Don't expect them to do a whole lot if there is a direct strike. They will go poof or at the least have unseen damage inside.

The feed line entrance should be a bulkhead of copper sheet/plate, which is also grounded, with a connector on the outside and inside (radio side).
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KB8BAB
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Posts: 101




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« Reply #2 on: June 18, 2012, 06:27:14 PM »

Exactly where is that second ground line to the "mains ground" running from? The tower?

I'd mount the arrestors on the outside of the house as close as possible to your station ground, which also should be outside and to which everything should be grounded. Don't expect them to do a whole lot if there is a direct strike. They will go poof or at the least have unseen damage inside.

The feed line entrance should be a bulkhead of copper sheet/plate, which is also grounded, with a connector on the outside and inside (radio side).


Sorry I should have elaborated...

- Tower is grounded to a ground rod located right next to the tower.
- The ground rod from the tower is also connected to the ground rod from the house using size 4 copper wire.

- I have on order a copper grounding bar that will be mounted on the outside of the house just below the feed entrance.
- The two lightning arrestors will be mounted to the grounding bar.
- The grounding bar itself will be connected to the ground rod at the antenna base using size 4 copper wire.

Do I bring in a ground from the grounding bar, to connect to the gear?
- I have some components with a three prong (grounded) plug, do these need to be grounded to the incoming ground as well?
- Would I not be creating a "ground loop" this way?

Bart
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K9KJM
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Posts: 2415




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« Reply #3 on: June 18, 2012, 09:48:09 PM »

Arrestors should be mounted right near where the coax feed line enters the building. Either indoors (As done at commercial towers) Or just outside.

A single ground rod at the tower is a start toward a ground system.  Space rods about twice the distance apart as the depth. 

Proper bonding of all grounds together is much more important than arrestors.

I do not have any of my radios connected to the ground system other than via the coax shield.
I want to put lightning energy to ground outdoors, Not THROUGH my equipment.

My tall towers are hit by direct lightning strikes most every storm, And like commercial tower sites, No damage to equipment.

For tips on how to do it on a low budget:
http://www.scribd.com/anon-849269/d/14868226-lightning-protectiontaming-thors-thunderon-a-budget

(Give that site plenty of time to load)
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K1CJS
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Posts: 6034




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« Reply #4 on: June 19, 2012, 03:51:35 AM »

KJM has it right.  Arrestors should be mounted on the outside of the building, as close as possible to the point where the cables enter the building.  Ground rod should be driven in there and connected (bonded) to both the tower ground and the building electrical ground.

Getting to the tower ground--you say a single ground rod?  That may well be inadaquate unless its a long driven ground pipe reaching the water table.  Most tower ground systems incorporate at least three ground rods surrounding the tower, and quite a few have a trio of ground rods at three points around the tower.

I would check the manufacturer specs for the recommended tower grounding system and also check with someone in your area who has done this type work before.  You may need to revise your ground system to get adaquate protection.
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K4SAV
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Posts: 1840




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« Reply #5 on: June 20, 2012, 09:59:04 AM »

You have gotten good advice so far.  I particularily like this one:

I do not have any of my radios connected to the ground system other than via the coax shield.
I want to put lightning energy to ground outdoors, Not THROUGH my equipment.

That's very true.  That's also contrary to most people's conceived notion that this must be a big short wire or strap.

- Tower is grounded to a ground rod located right next to the tower.

As others have already said, you need more than one ground rod.  The more ground rods you have at the tower, the less lightning current you will have going thru the ground wire to the house.  Most people recommend at least three rods. I usually recommend 9.  I have more than that.

- The ground rod from the tower is also connected to the ground rod from the house using size 4 copper wire.

Is that the ground rod at your radio entrance panel or the house AC entrance panel ground rod?  For minimum lightning current going thru your gear, the connection length between those two ground rods should be short. 

- I have on order a copper grounding bar that will be mounted on the outside of the house just below the feed entrance.
- The two lightning arrestors will be mounted to the grounding bar.
- The grounding bar itself will be connected to the ground rod at the antenna base using size 4 copper wire.
Do I bring in a ground from the grounding bar, to connect to the gear?

It sounds like your tower is very close to your house.   How far away is it?  The closer it is to the house, the more important the lenght of the wire connecting the radio entrance panel ground rod and the AC ground rod.  If the tower is close to the house, you don't have the large inductance of a long ground wire to the house.  That means there will be much more current directed toward the house, and that means you have to greatly minimize the voltage drop between the radio entrance panel ground rod and the AC ground rod to keep current from flowing thru your equipment.

- I have some components with a three prong (grounded) plug, do these need to be grounded to the incoming ground as well?
- Would I not be creating a "ground loop" this way?

When you tie the entrance panel ground to the AC entrance ground rod those grounds will be connected together outside the house.  They will also be connected together at your rig because both grounds tie to the chassis of your rig.   The ground loop which can cause a problem is when the outside connection between these grounds is long.  A voltage drop between these points will force current thru your rig.  To elminate the ground loop problem, the connection between these two ground rods much be short enough that they don't look like they are separate (minimum voltage drop between the two).  The only way to do that is to keep the wire short.  The impedance of that wire at high frequencies (lightning has a lot of those) is almost totally dependant on its inductance and that is dependant on its length.

Jerry, K4SAV
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KB3FFH
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Posts: 162




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« Reply #6 on: June 20, 2012, 04:42:52 PM »

Right outside the house is best, in case the coax gets hit between the tower and house. I had lighten hit the underground power lines near my house and it came in, went thru the house wiring than into my power supply. It was turned off. Jumped the off switch, went thru step down transformer, into radio and burned it up. If you can, disconnect both power and coax. Bill
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