Jim:
The position of the rods isn't going to make a lot of difference in
> how the current flows with respect to the house.
So the tower doesn't necessarily have to be concentric with the ground
rods circling the tower?
Is your tower on a foundation, or planted on the bare dirt?
The crank up tower It's anchored to a concrete foundation that's about 7
feet deep. The existing ground rods are about a foot away from the edge
of the foundation.
You can use strap if you find it mechanically convenient, but from a
> lightning impulse standpoint, round wire works just fine.
I'm glad to hear that because I already have some #2 solid and tinned
copper wire.
Thanks Jim.
Tony
On 4/14/2014 9:15 PM, Jim Lux wrote:
On 4/14/14, 5:48 PM, Tony wrote:
All:
My crank-up tower is located a few feet from the house and each leg is
attached to a ground rod that's about a foot or so away from the
foundation.
I'd like to add 3 more rods in a radial pattern to help "divert" a
potential lightning strike away from the house.
The position of the rods isn't going to make a lot of difference in
how the current flows with respect to the house. Is your tower on a
foundation, or planted on the bare dirt? If it's bolted to a
foundation, that will probably be the dominant current path to the
surrounding soil, because it's got a lot of surface area in contact
with the soil.
The grounds can't be
positioned 360 degrees around the tower due to it's close proximity to
the house so I'm not sure how critical that is.
More important is the spacing of the rods from each other. Two rods
driven 6" apart is basically one rod. Spacing them two rod lengths
apart is a good place to start. If you're worried about electrical
codes, 6 feet is the minimum spacing (of course, if you're driving 8
foot rods and you space them twice their length, then the 6 foot rule
is moot)
Any suggestions on this subject as well as rod spacing and copper strap
size would be appreciated.
You can use strap if you find it mechanically convenient, but from a
lightning impulse standpoint, round wire works just fine.
How big the wire has to be is more about mechanical ruggedness. AWG 6
is what the code requires, if you're stapling it to the house or
something, if it's hanging out #4.
"A 4 AWG or larger copper or aluminum grounding electrode conductor
shall be protected where exposed to physical damage.
A 6 AWG grounding electrode conductor that is free from exposure to
physical damage shall be permitted to be run along the surface of the
building construction without metal covering or protection where it is
securely fastened to the construction; otherwise, it shall be in rigid
metal conduit, intermediate metal conduit, rigid nonmetallic conduit,
electrical metallic tubing, or cable armor."
You can get a bit wrapped around the axle/prop shaft if you start
trying to differentiate between the "grounding electrode conductor"
(the wire from service disconnect/feeder to the FIRST ground rod) and
"bonding jumpers" (a wire between grounded stuff, including a pair of
rods).
It is ok by the code to do #4 from panel to first rod, then #6 from
there.
A lot of lightning protection systems use #2 everywhere. #2 is what's
required for a "ground ring" and if you're in the lightning protection
business, likely you've got a big spool of bare AWG2 on the truck, and
you just use it for everything.
Thanks
Tony
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