My house sits on directly on ledge and I have the rocks in the basement
area to prove it. Headspace goes from 7 ft in the back corner where my
furnace is to about 3 ft in the front of the house. The outside
perimeter sits on exposed ledge for about 90 percent of the perimeter
distance. The ledge extends out for 3 ft or better although parts of
the ledge may have 2-5 inches of earth cover. So do I drill an hole in
the ledge and drive some more rebar in to make my rf ground? Praying
has also come to mind and for 40 odd years it seems to have worked?
John / WA1JG
On 1/24/2012 3:47 PM, Stuart Rohre wrote:
> Technically, a ground wire covered by the deck is a violation of the
> National Electrical Code. Likely the rod was there first, and the deck
> was built over it.
> Breaker boxes, switched disconnects, panel boards and ground rods must
> be accessible for inspection and repair. It is common for ground rod
> connections to get disturbed by ground shifting, hit by grounds keeping
> equipment, etc. and thus require the clamp to be tightened over time.
> The typical house or ham ground rod does little to improve your RF
> performance, as the inductance of the long lead between the shack ground
> bus and the electrical entry ground rod will often mean you have a
> quarter wave situation at the high bands, ie high impedance at one end
> where your rig connects.
> Better to put a buried halo ground around the house outside the
> foundation, and connect, (bond) both electrical grounds and the
> communications grounds, as well as ham radio ground to it.
> That way, you have provided a physically short path to earth from any
> place in the house where the shack might be.
> Be aware however, everything bonded together, with the case of a less
> than good conducting earth, that you could have a hit on an antenna mast
> or tower, bonded to the common bus. The whole of the bonded system will
> rise to a very high potential, and might conduct harmful currents into
> equipment bonded to everything else. We had this happen at the club
> station: tower was hit, current came in on shields of coax, (coax was
> INSIDE the tower), and continued into the shack where it went around the
> room on our bus bar, up into a VHF radio, and vaporized the circuit
> board negative power trace before arcing through the power supply to the
> AC third pin ground path back to the AC utility ground.
> The ground bus was L shaped around two sides of the room and on the
> short side went out to a metal water supply piping system. Everything
> was bonded to it with wide flat conductors, thus low inductance.
> All AC outlets were bonded by the AC wiring (3 wire plus conduit).
> Sometimes it is just going to get you if equipment is left plugged in.
> Stuart Rohre
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