# [TowerTalk] Fwd: grounding (again)

Bob Shohet, KQ2M kq2m at kq2m.com
Wed Apr 25 14:06:53 EDT 2018

```Hi Jeff,

I have a 100’ Rohn 45 tower 70’ from the shack and a Rohn 130’ tower 120’ feet from the shack.  The two towers are also 120’ from each other.  I also have a 40 meter wire 4-square ~ 130’ from the 100’ tower and an 80 meter 4-square ~ 100’ from the 130’ tower.
I will try to diagram the situation...

40M 4-sq................<—130’—>..................100’ ^Rohn 45^................<--120’—>...........................130’ ^Rohn 45^

.................................Single pt Ground (Shack)........................................<—180’-->..................................................................80M 4-sq

The 40 M 4-square is ~ 200’ from the shack and the 80 M 4-sq is ~ 180’ from the shack.

This is not quite to scale but is the best that I could do.

I am now contemplating grounding the Comtek control boxes of both 4-squares to an 8’ ground rod where they are.

I am also still contemplating running an AWG 4 solid bare copper ground wire between the towers and using ground rods to ground it along the way.  I don’t know how deep I can get the ground rods into the soil because of the ledge on which the towers are located.  I do know that I can NOT run ground wires from the towers to the SPG (single point ground) because there is no soil between the towers and the SPG, only ledge!  There is  some soil between the towers however.   The SPG will also be connected underground via a buried perimeter ground to the utility (power), cable and telco grounds

I hope that I was able to make the situation relatively clear this time.

Tnx & 73

Bob  KQ2M

From: Jeff DePolo
Sent: Monday, April 23, 2018 4:00 PM
To: 'Bob Shohet, KQ2M' ; john at kk9a.com ; towertalk at contesting.com
Subject: Re: [TowerTalk] Fwd: grounding (again)

> Since #2 AWG Solid Bare Copper seems to be the favorite
>
> 1) For grounding purposes, does it matter if you use
> soft-drawn solid copper 2 AWG vs. hard-drawn solid copper 2 AWG?

Soft/annealed copper (I don't think "soft-drawn" is a correct term) is
preferred as it's more flexible and has slightly better conductivity.
Hard-drawn has a higher tensile strength making it useful for overhead power
and the like where it's under tension, but that's typically not a factor for
grounding.

> 2) Does it matter if the copper is solid/tinned vs. plain
> bare solid copper?

The main reason you see tinned #2 copper being used is that the rain run-off
from bare copper is bad for galvanized steel.  For example, if you have a
ground wire bonded to a tower, ice bridge post, or some other galvanized
steel object, whether attached mechanically or cadwelded, you should use
tinned to prevent the run-off from attacking the galv.

When buried, tinned can help prevent corrosion of copper for certain soil
pH's, at least for a little while...

> For (lightning) grounding runs of 100' or more, is the
> difference between 2 AWG solid bare copper and 4 AWG solid
> bare copper that significant?

A 100' long grounding conductor run would be a pretty ineffective ground
unless it's buried and/or you're planning to install a bunch of ground rods
along that length :-)  Please explain the layout.

--- Jeff WN3A

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