[TowerTalk] Question about ground

[Jim Lux]

On 9/9/12 3:54 PM, Matt Fearnow wrote:
> Hey all I'm relatively new. I'm running a ground for my ground rounds
> for antenna coax junction.  I have to go from my electrical service
> panel ground rod about 80'.
>

80 feet?  Do you actually need to run a separate ground bonding wire?  I
assume you have some sort of grounding at the antenna to which the
shields are bonded.  Then you have a grounding electrode at the house,
to which the shields are bonded.  I'm not sure you need a bonding wire, 
if everything is buried.  However, I will say that I pull a green wire 
ground along with 120VAC to receptacles out in the yard, and some of the 
runs are 80 feet long: but I don't have a separate grounding electrode 
out there.

The purpose of a bonding wire is to make sure that "ground" is at the
same potential at both ends.  In this case, you don't really care if the
"ground" is different out in the field than at the house.  What you care
about is that center conductor and shield and all the other wires, at
the house, go up and down together.

Are there other wires you're running out there in addition to the coax 
(e.g. rotator, weather station, relay controls)?

> 2 questions 1) how deep should trenching be?

Is it required to "meet code"?  Are your coax in conduit? Is it going to 
be under concrete?   Deep enough so it doesn't get dug up accidentally. 
  Rigid metal conduit and concrete can be buried less deep than bare 
cables (because an accidental shovel hit won't cause problems)

In California, in general:
24" for direct burial
6" for rigid or intermediate metal conduit
18" for non metallic raceway (plastic conduit, flexible or not)
12" for a 20 Amp or less branch circuit protected by GFCI (e.g an 
extension cord plugged into a GFCI outlet)
6" for irrigation/landscape light <30V if it's type UF or in a cable or 
conduit.

If it's in a trench with at least 2" concrete somewhere above, you can 
go 6" shallower (except for the two 6"ers)


Under a street, road, alley, private driveway, etc.  for 
non-residential, at least 24" for all
Residential driveways 12 or 18" depending.


What I do is rent a trencher, which usually cuts a more than 2 foot deep 
hole, and put it that deep.  If I need to come shallower (rocks, etc.), 
I put cheap concrete bricks over the top of plastic conduit..   I 
backfill to about 1 foot deep, then lay a plastic colored ribbon over it 
and complete the backfill.  Hopefully, if someone is digging with a 
shovel, they won't make it too deep on the first plunge, and they'll see 
the ribbon, or hit the bricks.





2) does brick dust used
> as a natural stone mulch, will that affect the ground wire?  Some
> areas it is only 1-3" others it seems to be 4-5" deep of brick
> stone.

I don't know.  It's basically fired clay, so I would think it's not much 
different than rock or soil.  Is it particularly alkaline or acidic, or 
likely to react with the copper?



>
> Thank you in advance for guidance.
>
> Matt Fearnow 73 - Matt - W9SIG
>
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