Grounding question - when your shack is on a second story

[wwhitby]

I've searched rr.com, but couldn't find anything similar. I'm going to install an outside antenna for my ATCSMon server. The PC and radio will be located in my library on the second story of our house. The LMR-400 coax will come in to the house through the soffit vent, about 8 feet above ground. I'm planning on grounding the coax's braid as well as installing a gas tube discharge-type lightning/surge protector. Both of those will be in a waterproof box attached to the mast. I'm also going to ground the mast as well.

My question is what is the maximum length that my ground wire for my coax should be? I could mount the box up around the 8 foot level of my soffit, but my gut is telling me that its too high and it should be closer to the ground.

What do y'all think?

Thanks,

Warren

 

[zz0468]

Just make it as short as you can, like a ground rod directly below the entrance point. The antenna mast should be grounded, and the coax should be grounded at the point that it leaves the mast toward the house. The surge protector should be located as close to the house as practical, and grounded at that point. An entrance at 8' above ground won't hurt anything, especially if you have a ground rod directly below the entrance.

 

[OceanaRadio]

2nd floor grounding

My question is what is the maximum length that my ground wire for my coax should be? I could mount the box up around the 8 foot level of my soffit, but my gut is telling me that its too high and it should be closer to the ground.

Well Warren, your gut answer may be the only thing between your plans and diaster then.

Maximum length for the coax shield-ground and arrestor(s) to the ground rod? About 12".

2nd story residential installations should ALWAYS run rooftop antenna coax down to earth (0' elev) first, shield-ground and install the arrestor(s) there, then come back up into the higher elevation shack.

Only a home constructed of structural steel could safely enter coax from above into a 2nd story elev. If that's not you, then I suggest you run the mast grounding wire _and_ coax to earth first, install the arrestor there, then find a way back upstairs to your library. Be sure to also bond that new ground rod to the same AC/service ground rod where hopefully your cable-tv/modem coax is also bonded.

The AC power supply to your computer, modem and radio also require surge protection. The tough deal there (on the second floor) is, the radio and coax-path OUT will likely be a much lower impedance than the homes flimsy AC ground wiring is, encouraging surge energy to jump the 2000v withstand of your radio or computer power supply and go right through the equipment on its way outside. Yes that coax arrestor will "fire" in reverse just as easy as the direction it is intended to, and if that energy is headed OUT of your radio it will not be a happy ending. Bottom line is, 2nd story shacks are the most difficult to adequately protect from damage. If they are also a long way from the AC/service entrance, the risk increases.

R/
Jack

 

[zz0468]

Well Warren, your gut answer may be the only thing between your plans and diaster then.

Maximum length for the coax shield-ground and arrestor(s) to the ground rod? About 12".

2nd story residential installations should ALWAYS run rooftop antenna coax down to earth (0' elev) first, shield-ground and install the arrestor(s) there, then come back up into the higher elevation shack.

Only a home constructed of structural steel could safely enter coax from above into a 2nd story elev. If that's not you, then I suggest you run the mast grounding wire _and_ coax to earth first, install the arrestor there, then find a way back upstairs to your library. Be sure to also bond that new ground rod to the same AC/service ground rod where hopefully your cable-tv/modem coax is also bonded.

The AC power supply to your computer, modem and radio also require surge protection. The tough deal there (on the second floor) is, the radio and coax-path OUT will likely be a much lower impedance than the homes flimsy AC ground wiring is, encouraging surge energy to jump the 2000v withstand of your radio or computer power supply and go right through the equipment on its way outside. Yes that coax arrestor will "fire" in reverse just as easy as the direction it is intended to, and if that energy is headed OUT of your radio it will not be a happy ending. Bottom line is, 2nd story shacks are the most difficult to adequately protect from damage. If they are also a long way from the AC/service entrance, the risk increases.

R/
Jack

Jack, I understand you're a purist when it comes to grounding, and you're generally technically correct - this post being no exception.

HOWEVER... sometimes the extra expense and effort can reach a point of diminishing returns. I have seen/been to/built countless commercial radio sites where the entrance ports are 8 feet or higher above the ground, and even some two story sites with entrance ports 15-20 feet high. In NO case, EVER, have I seen coaxes brought down to ground level, and then back up. That's NEVER, as in, IT ISN'T DONE THAT WAY. It's not done at broadcast sites, it's not done at commercial or public safety sites.

Supplemental classes and instruction I have received on grounding NEVER advocate bringing the coax to ground level. In many installations, it's just not practical, and the benefits do not outweigh the additional complication to the installation. Neither M/A Com's R3A nor Motorola's R56 documents advocate your methods.

What's generally done is, a ground conductor is bonded to the cable shield, and then grounded directly below the entrance port. It's also grounded at the tower/mast at the point the run turns from vertical to horizontal, with the ground conductor continuing the vertical run to ground.

I can't help but feel that conflicting advice on grounding only serves to cloud the issue, not clarify. The current methods of grounding have proven to be effective. We're protecting against the of chance of a lightning strike, not trying to harden a site against nuclear EMP.

 

[KC4RAF]

zz0468 is correct.

NEC addresses the issue of grounding antennas and towers, etc.

 

[OceanaRadio]

Jack, I understand you're a purist when it comes to grounding, and you're generally technically correct - this post being no exception.

HOWEVER... sometimes the extra expense and effort can reach a point of diminishing returns. I have seen/been to/built countless commercial radio sites where the entrance ports are 8 feet or higher above the ground, and even some two story sites with entrance ports 15-20 feet high. In NO case, EVER, have I seen coaxes brought down to ground level, and then back up. That's NEVER, as in, IT ISN'T DONE THAT WAY. It's not done at broadcast sites, it's not done at commercial or public safety sites.

Supplemental classes and instruction I have received on grounding NEVER advocate bringing the coax to ground level. In many installations, it's just not practical, and the benefits do not outweigh the additional complication to the installation. Neither M/A Com's R3A nor Motorola's R56 documents advocate your methods.

What's generally done is, a ground conductor is bonded to the cable shield, and then grounded directly below the entrance port. It's also grounded at the tower/mast at the point the run turns from vertical to horizontal, with the ground conductor continuing the vertical run to ground.

I can't help but feel that conflicting advice on grounding only serves to cloud the issue, not clarify. The current methods of grounding have proven to be effective. We're protecting against the of chance of a lightning strike, not trying to harden a site against nuclear EMP.

My friend zz0468 (who along with others provide great answers and advice here), and others who missed details in my original post:

I was clear in what the exception could be to a 2nd story residential entrance level for coax, to wit: "the residence would have to be constructed of structural steel" For those who actually understand the NEC/NFPA and don't just refer to it, this means that the entire structure is bonded, floor-to-floor, from the 100th story to the ground. Of course radio stations can and do exist on the 100th floor and their coax enter directly from a roof-peak mount. The structural steel bonding of the entire structure, peak to earth is the permitting factor there. And so would be a residence IF it was built with structural steel.

Communication huts that enter coax at the 6' or 8' levels either have structural steel, AND/OR they use a two halo-ring system, one at the entrance level and and/or another at ground level. That minimizes the enormous potential that would otherwise exist from even a 6' or 8' potential between the entrance-lvel and earth-ground level. There is no debating this scientific fact. A home built of brick and sticks cannot safely enter coax from a rooftop mast directly into the 2nd floor level, no matter how fat the grounding and bonding conductor is to the nearest ground rod. The fact that hams all over the world ignore this simple rule to their own peril is only proof of the rules, not an excuse to follow (their) poor practices.

Finally as to the facts, you will not find a diagram or printed instruction in the NEC or NFPA-780 that depicts coax entry until it has shield-grounded at the AC/service entrance.

Government and commercial communication system design goes to great lengths to minimize the potential damage from lighting. I have never implied that a residential installation should try to mimic the extreme of those standards, unless cost was no issue. But I do stress that a residential owner should establish by standard basis whether they are subject to lightning strikes, and if they are, to work and live accordingly. There is no hobby or volunteer effort using your home as a base, that is worth its destruction by lightning.

R/
Jack

 

[BuffaloJustice]

There is no hobby or volunteer effort using your home as a base, that is worth its destruction by lightning.

Or the death of the user for that matter.

The little bit of lightning pro that I have learned says to have as low an impedance to ground as possible. I am by no means an expert but I have been researching grounding and bonding extensively the last couple of weeks. An extra 16 feet of cable in this case will not only do that but also raise the impedance into the house. For little extra expense and signal loss I would go all the way to ground. Also, do bond the mast/coax ground to the home main ground and check your home wiring for any sneak paths. A scanner is cheap your home is not, and your life is immeasurable!

 

[smokeyjones666]

I like my house, I like my computer equipment and I like my life. If you feel the same way, I suggest you follow Jack's advice and bring the coax and grounding conductor down and ground it there. Don't forget to bond the antenna ground to the ground electrode at the service entrance - not only is it what the NEC says to do, it's just a good idea. If you can't get it near, use a series of 8' ground rods bonded to the service entrance.

 

[N1SQB]

The coax should be grounded at the point that it leaves the mast toward the house.

I agree but exactly HOW do you do that? What materials do you use on coax lines? I have my 20 foot pole for example, mounted off the side of my deck. The pole ends about 3 feet off the ground. I have heavy gage wire going from the bottom of the pole right to an 8 foot ground rod directly below. How do I ground the coax. Im interested and I want to do it for additional safety. I believe in it .

Manny

 

[tonsoffun]

I agree but exactly HOW do you do that? What materials do you use on coax lines? I have my 20 foot pole for example, mounted off the side of my deck. The pole ends about 3 feet off the ground. I have heavy gage wire going from the bottom of the pole right to an 8 foot ground rod directly below. How do I ground the coax. Im interested and I want to do it for additional safety. I believe in it .

Manny

Hey Manny,

Take a look at my little article in the Wiki, it should give you some idea on how to do this. By the way, your new antenna set up looks great!

Grounding Bulkhead with supressors for your scanning station - The RadioReference Wiki

You don't need to go into this kind of detail but just to give you some idea
Here is a few pics:

Ron

 

[N1SQB]

Hey Manny,

Take a look at my little article in the Wiki, it should give you some idea on how to do this. By the way, your new antenna set up looks great!

Grounding Bulkhead with supressors for your scanning station - The RadioReference Wiki

You don't need to go into this kind of detail but just to give you some idea
Here is a few pics:

Ron

WOW!
Thanks for the compliment on my new antenna set up but to be honest, your set up dwarfs mine....LOL Nice article by the way. I have some new ideas now...

Manny

 

[BuffaloJustice]

Here's a good article on lightning protection for the little guys. There are three parts and it a real breeze to read.

http://www.arrl.org/tis/info/pdf/0206056.pdf

http://www.arrl.org/tis/info/pdf/0207048.pdf

http://www.arrl.org/tis/info/pdf/0208053.pdf

BTW, tonsoffun, I saw your tilt over in the wiki a while back and that's what I plan to use when I get some good weather that lasts more than an afternoon. Very inspirational, thanks for taking the time to put it up.

 

[N1SQB]

Its funny. I did a goggle search on grounding and ran into that very same article. Thanks for posting it.

Manny

 

[tonsoffun]

BTW, tonsoffun, I saw your tilt over in the wiki a while back and that's what I plan to use when I get some good weather that lasts more than an afternoon. Very inspirational, thanks for taking the time to put it up.

No problem Buffalo, thats what its there for.

Ron