Grounding a DB4e setup in South Florida

[billg]

Hi All,

I'm getting ready to DIY a new setup based on the advice from this thread:

http://forum.tvfool.com/showthread.p...ed=1#post46817

I will have to experiment with tripod vs mast installation on my roof and chimney, but either way I will be putting a big metal spike on my metal roof down here in lightning-prone South Florida.

I was planning to use something like this to ground the coax coming from the antenna into the house:

http://www.amazon.com/gp/product/B00...=A1SRR0B7QVPEN

Unfortunately the antenna won't be anywhere near my utility service, so I'll be attaching it to as big of a grounding rod as I can get into the ground, with #12 copper wire.

I presume it's still a good idea to ground the antenna itself though, right? I'm less clear on best practices for doing that. Assuming I can use the same grounding rod and #12 wire, can I run the grounding wire alongside the coax (since they'll be going to approximately the same place), or will that introduce noise or other unintended consequences? Can I run the wire right along my roof, or is it better/required to put it in nonconductive conduit, elevate it, or otherwise treat it differently? Is #12 even heavy enough for this application? I'm going to need probably close to 25' to get from the antenna to the ground (though the house is only a single story).

Any advice/best practices would be appreciated.

[timgr]

Originally Posted by billg

Hi All,

I'm getting ready to DIY a new setup based on the advice from this thread:

http://forum.tvfool.com/showthread.p...ed=1#post46817

I will have to experiment with tripod vs mast installation on my roof and chimney, but either way I will be putting a big metal spike on my metal roof down here in lightning-prone South Florida.

I was planning to use something like this to ground the coax coming from the antenna into the house:

http://www.amazon.com/gp/product/B00...=A1SRR0B7QVPEN

Unfortunately the antenna won't be anywhere near my utility service, so I'll be attaching it to as big of a grounding rod as I can get into the ground, with #12 copper wire.

I presume it's still a good idea to ground the antenna itself though, right? I'm less clear on best practices for doing that. Assuming I can use the same grounding rod and #12 wire, can I run the grounding wire alongside the coax (since they'll be going to approximately the same place), or will that introduce noise or other unintended consequences? Can I run the wire right along my roof, or is it better/required to put it in nonconductive conduit, elevate it, or otherwise treat it differently? Is #12 even heavy enough for this application? I'm going to need probably close to 25' to get from the antenna to the ground (though the house is only a single story).

Any advice/best practices would be appreciated.

There is a lot of lightning in Florida, isn't there?

I would put a ground clamp on the mast and run #6 or larger copper wire to the service ground of your house. You can buy any length of solid #6 copper wire that you need from sellers on eBay. Cheaper than any local source I've found, and you can buy whatever length you need.

Grounding is covered a lot in older posts, including this recent post - http://forum.tvfool.com/showpost.php...11&postcount=9

Note that dedicated lightning rods use even larger wire for their down leads, like #4 braided copper wire. You could use this instead, but it's significantly more expensive than the #6 solid wire.

[billg]

Thanks for the advice. If an 8' rod is required I might have to look into reaching the service ground, as I'm pretty sure there's only about 6' of ground underneath me before I hit the water

Looking at eBay, you're right -- the solid wire there is MUCH cheaper than the electrical supply house in my area (or Home Depot/Lowes, certainly).

[GroundUrMast]

Building separate grounding systems very often leaves you with a potentially dangerous situation...

If the antenna system is connected to an isolated ground rod, the resistance of the soil between your electrical service ground and the antenna system rod will allow high voltage differences to develop between the antenna system parts and the rest of the grounded items in the home.

If a nearby lighting strike induces a fault current of 500 amps in the antenna ground system and the ground rod resistance is only 2 ohms (an excellent and almost impossible value to achieve value in practice), Ohms law says you would expect to see 1000 volts difference between the antenna system and your TV chassis if it's connected to an outlet.

Please, bond the antenna system to the electrical service ground. This is the only way to achieve a connection with a resistance low enough to truly protect you and your property.

The NEC calls for #10 AWG copper at a minimum for the connection from the mast to ground, and the same for the coax grounding block to ground. Heavier gauge wire is even better given it's lower resistance.

If you add a new ground rod, the NEC calls for it to be bonded to your existing electrical service grounding system. The smallest diameter wire allowed by the NEC for this purpose is #6 AWG copper.

http://forum.tvfool.com/showthread.php?t=901

The ultimate purpose of 'grounding' is not to simply connect to earth... But rather, to prevent large voltage differences from developing between objects that could become energized due to a fault. The connection to earth is only one element in the overall method and plan. Properly sized conductors and reliable connections are vital parts of the overall plan to ensure than hazardous voltages differences can be prevented while safely conducting reasonably anticipated fault current(s).

[billg]

Ah, so you're taking the Fear of God (tm) approach.

Well, I've seen enough nearby lightning strikes that that makes sense. My main problem is that my electrical service ground is about 70' away (as the crow flies) and probably more like 150' away from the most practical spot to put the antenna (our home is an odd design that consists of two buildings connected by a covered breezeway). I presume that at a certain distance the ground wire is going to be less effective, right? Should I try to split the difference, or run as short a ground wire as possible and have to deal with a much longer coax run?

Thanks again for all of the great information!

[timgr]

Originally Posted by billg

Ah, so you're taking the Fear of God (tm) approach.

Well, I've seen enough nearby lightning strikes that that makes sense. My main problem is that my electrical service ground is about 70' away (as the crow flies) and probably more like 150' away from the most practical spot to put the antenna (our home is an odd design that consists of two buildings connected by a covered breezeway). I presume that at a certain distance the ground wire is going to be less effective, right? Should I try to split the difference, or run as short a ground wire as possible and have to deal with a much longer coax run?

Thanks again for all of the great information!

Maybe you don't appreciate the difference in the resistance of a copper wire compared with the resistance of the earth between the two ground rods, one at your tower and the other serving your house. The resistance of #6 copper wire is about 0.4 ohms per 1000 ft. If the ground resistance between is optimistically 2 ohms, that's about 50 times the resistance of that 100 ft of copper wire. Use a larger wire, and the difference becomes even larger. Two #6 wires in parallel is now 100 times difference. A single 1/0 wire has less than 1/4 the resistance of a #6 wire, making the difference 200 times. This brings that 1000 volt potential difference between the tower and the house in GroundUrMast's example down to 20, 10 and 5 volts, respectively. It's Ohm's law.

This is a big difference. Voltages above 600V placed across dry skin will break down the skin barrier and conduct through the aqueous tissue below - causing a huge jump in conductivity. The difference in risk of electrocution is significant.

My advice - put the tower where you want it, and buy enough heavy wire to bond the tower to the building ground. The distances you are talking about are not far compared to the earth potential differences without the bonding wire.

[timgr]

Also, reaching the water table would be a good thing.

"Since moisture becomes more stable at greater distances below the surface of the earth, grounding (earthing) systems appear to be more effective if the grounding electrode can reach the water table."

http://www.mikeholt.com/videodisplaynew.php?pageid=4134