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Author Topic: Which cable or wire for lightning/static ground?  (Read 4437 times)
W9KDX
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Posts: 771




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« on: March 03, 2012, 11:55:12 AM »

I see differing opinions; which is right for an external connection from the antenna wire junction connectors to the outside ground rod?  I hear that the surface area of the flat ground strap is better but I also hear that 6 gauge copper wire is better.

Thanks
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Sam
W9KDX
N4CR
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Posts: 1701




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« Reply #1 on: March 03, 2012, 01:45:24 PM »

For static, any conductor will do. Even one with high resistance.

If all you were concerned about was the resistance to ground it wouldn't matter. Any conductor of the same material and the same cross section would work the same way to conduct electrons.

Lightning is not just a huge DC pulse. It has harmonics going way up into the HF bands. So you have to treat it like DC with a huge AC/RF potential. As such, you want the lowest impedance conductor you can find. The large skin area of copper strap increases the area for skin effect and thus lowers the impedance much more than the round conductor even if they have the same DC resistance.

Copper strap wins by a mile for conducting lightning pulses.

Here's some good reference material.

http://www.solacity.com/Grounding.htm
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73 de N4CR, Phil

Never believe an atom. They make up everything.
W6RMK
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« Reply #2 on: March 03, 2012, 01:56:57 PM »

For the same amount of copper, the inductance of strap is not much lower than solid or tube conductors.  You're thinking skin effect where surface area matters, but that's about AC resistance.   For lightning, inductance effects dominate, so use what ever is cheaper.  If its an RF ground for a vertical antenna, resistance matters, use strap.
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W9KDX
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« Reply #3 on: March 03, 2012, 02:58:44 PM »

Is this stuff:

http://www.universal-radio.com/catalog/cable/4607.html

suitable for outside lightning/static ground?  I am passing coax through the wall and this will ground the plate where the coax connectors couple, using a coax surge protector.

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Sam
W9KDX
AC5UP
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« Reply #4 on: March 03, 2012, 03:29:38 PM »

I see differing opinions; which is right for an external connection from the antenna wire junction connectors to the outside ground rod?  I hear that the surface area of the flat ground strap is better but I also hear that 6 gauge copper wire is better.

When you see the word 'strap' in this context it's more likely referring to solid flat copper like that used for flashing by the roofing trade. Flat tinned braid is lovely stuff in terms of flexibility and ease of installation but should be avoided whenever there's a chance it will become weathered. Instead of acting like one large conductor when new, oxidized braid breaks down into a multitude of poor pathways and can also become brittle.

If you can handle the cost and challenge of installing copper flashing / copper strap, consider it. Otherwise #6 or heavier stranded insulated copper wire is a very popular choice especially if your local HandyGuy store discounts "short ends".

BTW: If you patch the entry hole with mortar it's generally not a good idea to allow direct contact between copper and concrete. Slow chemical reaction and a plastic like PVC between the two is good.
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WB4SPT
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« Reply #5 on: March 03, 2012, 03:51:40 PM »

Is this stuff:

http://www.universal-radio.com/catalog/cable/4607.html

suitable for outside lightning/static ground?  I am passing coax through the wall and this will ground the plate where the coax connectors couple, using a coax surge protector.



That is fine for equipment grounding/bonding, but at 14AWG don't put it in the path of lightning!  To deal with possible lightning coming down the coax(s), you NEED to get a larger conductor to bond to a local ground rod (or two) (#6 AWG is fine), and then a larger conductor to bond to your home entrance ground system.  I use a 2" solid strap .020 thick buried on the way.  Georgia Copper has this.  So, it could go like this:   Heavy strap from your coax connector plate to your home service ground system;  #6 AWG solid to run to your local ground rods to the coax plate, and then a braided strap, #12 or larger equiv to your gear inside (from the coax plate).  Also, pick up any surge protectors, UPS, outlet strips to this same braided strap.  This is not an exhaustive treatment, but a decent start.  If there are rotator cables, TV antennas, those need penetration protection as well.  Don't solder any of this.  Use either yellow/red metal connection hardware and/or hard braze. 
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W9KDX
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« Reply #6 on: March 03, 2012, 05:26:45 PM »

I understand the procedure for grounding with the home ground, however it will just not be feasible here, so my equipment will be totally isolated from any electrical connections in the home as well as disconnected from the antennas.  Consequently, the only ground needed is for the antennas (not drilled into concrete, but wood). 

It sounds like the #6 AWG solid is the way to go.

Much thanks.
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Sam
W9KDX
N4CR
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« Reply #7 on: March 03, 2012, 07:06:54 PM »

Why do your antennas need a ground? What antennas are you grounding?
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73 de N4CR, Phil

Never believe an atom. They make up everything.
W6RMK
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« Reply #8 on: March 03, 2012, 08:36:21 PM »

I understand the procedure for grounding with the home ground, however it will just not be feasible here, so my equipment will be totally isolated from any electrical connections in the home as well as disconnected from the antennas.  Consequently, the only ground needed is for the antennas (not drilled into concrete, but wood). 

It sounds like the #6 AWG solid is the way to go.

Much thanks.

Electrical code, should you decide to follow it, requires that all grounding electrodes be bonded by AWG6 or larger conductor (there are some exceptions, but that's the general rule).

I'd find it hard to believe you're totally isolated, unless all your gear is battery powered and you never hook up something with a wall wart or battery charger.

But yes, AWG 6 is the way to go.  Easy to connect, easy to buy, etc.
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K9KJM
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« Reply #9 on: March 03, 2012, 10:05:55 PM »

The braided material in the Universal ad is NOT what you want for a ground conductor.
That type of material is nice for doing things like bonding a steel door to a steel door frame, etc.  Where the ground conductor needs to flex a lot.

The copper strap mentioned is just flat copper strap, Sometimes available from local upscale roofers, Who use it as roof flashing material.  Or it can be purchased from a discount home supply store in the roofing department.
A cheaper alternative than the solid copper wire can be some copper tubing, Sold in rolls in the plumbing department of the same discount home supply store.   If using the soft copper tubing, Do use caution to not kink it, One of the disadvantages of using tubing. It is not as durable as solid wire.  Whatever you do use, Make all bends gradual, No sharp bends.
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W9KDX
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« Reply #10 on: March 04, 2012, 07:19:52 AM »

Why do your antennas need a ground? What antennas are you grounding?

Well, maybe I am wrong, wouldn't be the first time, but when I put a big stretch of wire into the air, and attach it to my house, I figured I should ground it.

I have 2 dipole antennas with coax leading to a plate mounted onto the wood joists on the house.  I use coax connectors to pass through the holes and attach PL-259s on the other side.  I disconnect these on the house side when not in use.  I also disconnect from AC when not in use.  All equipment inside is appropriately connected to the home ground.

You are right, I am only isolated when I am not working the bands, but I don't use the equipment when there is a storm.

I assume I need to ground the antennas at the plate outside, I have 2 surge protectors and assumed I need to also ground these outside.  I expect to use the #6 copper wire.

Let me know where I am wrong.

Thanks
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Sam
W9KDX
AC5UP
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« Reply #11 on: March 04, 2012, 10:12:26 AM »

Well, maybe I am wrong, wouldn't be the first time, but when I put a big stretch of wire into the air, and attach it to my house, I figured I should ground it.

There are two reasons to ground an antenna... Static / lightning discharge and, in the case of an unbalanced (longwire) antenna, an RF counterpoise.

Since you mentioned you have two dipoles, they are balanced antennas that need no ground and if you add a ground the wrong way you could screw up their balance. What you likely want is a static discharge ground and the best place for that is where the coax enters the house. Install a ground rod or two at the entry point and bond it (them) to the shield of the coax. One common method involves a barrel connector between two PL-259's, hose clamps, and a short piece of heavy wire between the coax and ground rod.

Weatherproof as needed.

Basic concept is to give any induced surge a nice fat path to ground BEFORE it needs to enter the house and go doodling around in the radio room. Lightning is an outside toy, ya' know.........  Cheesy
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W9KDX
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Posts: 771




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« Reply #12 on: March 04, 2012, 10:38:48 AM »

Well, maybe I am wrong, wouldn't be the first time, but when I put a big stretch of wire into the air, and attach it to my house, I figured I should ground it.

There are two reasons to ground an antenna... Static / lightning discharge and, in the case of an unbalanced (longwire) antenna, an RF counterpoise.

Since you mentioned you have two dipoles, they are balanced antennas that need no ground and if you add a ground the wrong way you could screw up their balance. What you likely want is a static discharge ground and the best place for that is where the coax enters the house. Install a ground rod or two at the entry point and bond it (them) to the shield of the coax. One common method involves a barrel connector between two PL-259's, hose clamps, and a short piece of heavy wire between the coax and ground rod.

Weatherproof as needed.

Basic concept is to give any induced surge a nice fat path to ground BEFORE it needs to enter the house and go doodling around in the radio room. Lightning is an outside toy, ya' know.........  Cheesy

What gauge of wire do I need to the ground rod?  This is exactly what I am doing, using commercial surge protectors between the coax coming down where it enters the house.
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Sam
W9KDX
AC5UP
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Posts: 3956




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« Reply #13 on: March 04, 2012, 11:41:01 AM »

What gauge of wire do I need to the ground rod?

The heavier the better. You want something capable of handling (or trying to handle) an ungodly surge and the more of it that dissipates outside the less there is to dissipate inside. Next time you're at your local HandyGuy store look in electrical for "short ends" near the big spools they cut to length. Sometimes you can get a deal, sometimes not, #6 copper or better and double clamp or braze all connections.

A decent surge can un-solder a truly nice connection before the peak of the surge tries to reach ground. Think in terms of the weakest point being strong enough to handle a short walk through hell..............
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W9KDX
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Posts: 771




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« Reply #14 on: March 04, 2012, 02:48:34 PM »

Much thanks.  #6 is in the budget and all connections will be clamped.   

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Sam
W9KDX
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