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Author Topic: Ground Bus Location  (Read 340 times)
N1NRK
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Posts: 13




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« on: June 11, 2009, 12:20:50 PM »

I know this topic has been beaten to death, but I still have questions.  

My shack is in my basement and my coax leads have to cross about 10' of ceiling then down the wall before it finds my radios.  I'm trying to put together a grounding solution, and have some lightning arrestors, copper bar, etc.  My question is that everything seems to state that I would need a single point ground, which would require that I place the bus bar (to mount the lightning arrestors) inside the house.  However, that would potentially bring lightning inside the house, via the coax, which EVERYTHING says not to do.  From this SPG, I would then have to route a ground wire back out to my ground rod (in the back yard at cable entrance).  I then intend to run a wire around the house to the front, where my service entrance is to bond them together.  

Should I instead mount the bus bar (with arrestors) in an enclosure on the back side of the house, connect to rod, then run "protected" coax into the shack?  It seems the more I read and more pictures I see, the more confused I get.

Thanks in advance for any advice you may have.

73s

Keith/N1NRK
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AI7RR
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Posts: 164




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« Reply #1 on: June 11, 2009, 12:28:03 PM »

You're SPG should actually be outside with lightning protection and ground rod terminations on it. Also from the SPG, run a #2 stranded into the shack to another bus bar that your radios and accessories are grounded to. Don't daisy chain.

73,, Roger
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KB9CRY
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« Reply #2 on: June 11, 2009, 04:40:33 PM »

Mounted just inside of where this would connect to your outside ground rod(s) is fine.  As long as the connection from buss to the rods outdoors is low impedance, meaning at least #6 wire min or wide copper strip.
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WB5JEO
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« Reply #3 on: June 11, 2009, 08:11:42 PM »

I would definitely set the ground point near where the coax enters the house, outside or just inside, if that's not possible. But you also need to think about getting your equipment grounded back to the single point or at least providing a short path to a ground rod system close to the radio room.

There's ideal, and then there's what you can do. You might be only able to run some hefty ground paths back from the equipment to the ground bar. You don't want to ignore what can come in on the AC line, now that you've given your stuff an attractive path back to the SPG. You can somewhat deal with that by protecting the main house AC feed with an appropriate device and a REAL ground system for the AC system. The usual wire from the load center to a single (often poor zinc plated ground rod) is lame.
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N3OX
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« Reply #4 on: June 11, 2009, 08:41:31 PM »

"You can somewhat deal with that by protecting the main house AC feed with an appropriate device and a REAL ground system for the AC system."

When you BOND your AC service ground to your shiny new outdoor ground system by running a big heavy wire outdoors, you very much limit the chances of developing a big voltage between your outlets' third wire and your station ground.

Adding a couple extra new deep rods for the AC service can be part of your overall plan, but the bonding is the real key.

That's the point of the "single point ground,"that all the grounds that your station uses, outdoor lightning protection, AC load center, whatever, be bonded in a low impedance way to a common point to minimize the potential differences between them and to try to minimize ground loops.

You need a gigantic outdoor ground system to keep your radio station equipment from coming up to some nonnegligible voltage if you get hit.  Most hams can't have that.  So the next best thing is that all of the equipment simultaneously "jumps" voltage together.

You also need SOME ground stakes to make sure you don't develop hundreds of thousands of volts with respect to ground on your equipment cases, because that just brings your lightning bolt inside, and that's the worst of all.

But if you do the bonding to a common entrance panel with coax shields connected (and arrestors if you've got 'em) and you have some outdoor ground rods, there's really no need to run any extra dedicated ground conductors inside the house.  In fact, to do so could make low impedance ground loops and you don't want that.

Ideally, any current that wants to flow between various grounds, like when the power lines get hit and your tower didn't, will do so 99.999% through your outdoor bonding conductors.

73
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
K9KJM
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Posts: 2416




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« Reply #5 on: June 12, 2009, 12:54:50 AM »

The ideal place for your "Single Point Ground" panel is near where the coax enters the building. (NOTE that almost ALL commercial radio stations with TALL towers that take direct lightning strikes have that single point ground panel INSIDE the building, (But grounding to the outdoor ground system with lots of wide flat copper strap.)

Ham stations are sometimes a compromise. IF you will be having coax switches also mounted on your single point ground panel, Having it right where the coax enters the building may not be the easiest way to operate........     In that case, It may be better to move the panel closer to the operating position and also make sure you properly ground the coax shields before they enter the building.

While #6 copper is given as a minimum size conductor to use for lightning protection, That is mostly for bonding ground rods together, etc.  The best material by far for grounding coax switches, arrestors,etc is flat copper strap. (Copper roof flashing of .022" thick usually works well)

For some good information:
http://members.cox.net/pc-usa/station/ground3.htm
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WB5JEO
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« Reply #6 on: June 12, 2009, 07:40:44 AM »

And since a really good lightning protection system is a major project, think about getting the basics done, but lay out a plan that can be extended a bit at a time. I'm getting a tower up at my new location. I'll have more done on this one than I've ever had before (high exposed location), but over time, I'll expand the ground system a lot more. I accept that, right now, I don't expect to take a direct hit with no damage, even with everything bonded. Commercial stations can spend more on this than the equipment, but the cost of a good amateur system can approach the cost of a nice radio. But I'll have substantial protection and a clear plan to improve. But do real things to each part of the system. Neglecting any one of them can leave you worse off than nothing at all, if you end up directing a strike at one point through your equipment back to your nice tower ground.
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