On 6/20/2010 11:33 AM, Jim Brown wrote:
> On Sun, 20 Jun 2010 07:31:57 -0700, jimlux wrote:
>
>
>> Gary Schafer wrote:
>>
>>> I would stay a few feet away from the house. The ground right near the
>>> foundation is dryer than it is out away from the house. Where the rain drips
>>> off the roof may not be a bad place as it gets more moisture when it rains,
>>> the time you also worry about lightning.
>>>
>>>
>
>> Good point... Although, the whole discussion strikes me as a
>> "overthinking" the problem a bit.. A few feet one way or another
>> probably doesn't make much difference.
>>
When you get "up here", most homes have basements and the first three
feet (give or take a tad) around the basement walls or foundation is
sand. In the case of the basement there is a "weep tile" at the bottom
of the back fill which is a bit deeper than the foundation. Typically
there is about 6" to a foot of top soil over the back fill for flowers,
shrubs, or what ever. Outside the back fill is the native soil which
varies widely from one location to another, but this soil typically has
a much higher conductivity (quite often acidic) than does the sand in
the back fill. An 8' ground rod would not even reach the base of the
back fill while a 10 footer might just touch it with a good likely hood
of puncturing and ruining the weep tile.
NOTE when driving ground rods close to a home that has a basement,
remember there are weep tile about a foot to 16 inches out from the
outside edge of the basement wall. In homes older than about 20 years
this weep tile is likely to be just that. Tile! and not the perforated
hose now used in place of field tile. OTOH there is no guarantee that a
newer home doesn't have tile. So always give that buried tile at least a
foot of clearance. If you drive a rod into that tile, dirt can get in
and plug it for some distance heading toward the sump. fixing it can be
quite expensive.
The 5th photo down on
http://www.rogerhalstead.com/ham_files/cablebox.htm shows how deep this
back fill can be and the man in the trench is standing on at least a
foot of pea gravel covered with sand. They are sealing the wall down to
the foundation.
Although I have a pair of bare #2 copper ground cables running along
with the conduit, there are runs (not shown) that go out into the yard
perpendicular to those cables with the first 8' ground rod being about a
foot farther out into the native soil.
The sand back fill except for maybe the top foot or two is moist all
year round. Out in the yard the water table varies from maybe a foot
below the surface in the spring although at times it appears to be above
the surface <:-)). By fall, the water table is roughly 5' down. So
there is always some flow into the sump from the weep tile.
The ground rods for the entrance bulkhead are about 4' out from the
basement wall.
73
Roger (K8RI)
> I don't see this as "over-thinking" at all -- rather I see it as quite
> practical advice. I have flowers and shrubs close to my house, and those that
> are protected by some sort of roof overhang get a LOT less moisture than the
> soil only a foot or so away that is not protected.
>
> Overall, Gary's advice is pretty much on target. He's found the fundamentally
> sound grain of truth in the often over-blown and mis-applied single point
> ground concept. Well done!
>
> 73, Jim Brown K9YC
>
>
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