[TowerTalk] Filter location and grounding rods

Jim Lux jimlux at earthlink.net
Thu Dec 19 08:28:15 EST 2013


On 12/18/13 9:05 PM, Hans Hammarquist wrote:
> Gentlemen,
>
>
> Two questions regarding the finishing of my new radio shack:
>
> Where to put a power line filter:
>
>
> The shack is totaly shielded (wrapped in aluminum foil and copper
> wires) and I am planning to put filter on the power line entering the
> shack. The shack is located around 12 feet from the main house. I
> have a conduit burried between the house and the shack. Now, where is
> the best place for a line filter? Shall I put it there the power line
> exiting the house or there it entering the shack?


Is the filter to prevent transients getting in, or RF getting out?

Is it protecting the house or the shack?

Put it at the wall of the thing it is protecting.

>
>
> Grounding rods:
>
>
> Grounding the shack, I am planning to put a couple of grounding rods
> around the shack. I heard somewhere tha it is more efficient to use
> several short (4 feet) grounding rods than one long (8 fet) rod. Does
> anyone knows how many short rods are needed for each long rod or is
> this a fractional number?


Are you subject to National Electrical Code or something similar?  4 
foot rods don't meet code.

There's two aspects to the rods (which don't make a very good ground, by 
the way).. one is "area of conductor in contact with the soil", and the 
other is "conductivity of the soil".  A third less important aspect is 
"how good is the contact of the conductor with the soil".

Soil near the surface tends to have lower conductivity and poorer 
contact (it's disturbed, drier, etc.), so the preference is for deeper 
contact (e.g. drive the 8-10 foot rod deep into undisturbed soil).

You can bury the rod sideways in a trench (and that meets code).

A *much* better ground is a Ufer ground (concrete encased grounding 
electrode): typically you get this by laying a 20 foot wire in the forms 
before pouring the foundation, or by bonding a wire to the rebar. Lots 
of contact area between concrete and soil, lots of contact between wire 
and concrete, well protected, etc.

ANother ground, if you're not doing Ufer, is a ring ground: dig a trench 
around your shack and lay a AWG 2 wire in it as your ground.  Lots of 
contact area, spreads the current over a large area, and because it's 
physically large, a soil issue in one place is unlikely to affect another.

Is your conduit run made of metal? a 12 foot buried metal conduit would 
make a fairly decent electrode.

I can't recall if the two building electrical systems need to be bonded, 
and if you will need to have a new grounding electrode for the neutral 
at the shack. It's either that or you need to run a bonding wire from 
your house to your shack for the "green wire ground". You'll need to 
check the code.  In any case, your shack grounding system needs to be 
bonded to the greenwire ground in your shack.





>
>
> With best 73 de,
>
>
> Hans - N2JFS _______________________________________________
>
>
>
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