Actually moist concrete is a very good conductor. Connecting to the rebar in the
concrete makes an excellent ground system. But you need to weld the connections
of the rebar inside the concrete or when you get a lightning strike you can get
an arc inside and the concrete will explode. This type of ground is called a
Ufer ground. Named after the guy that invented it.
The fact that concrete holds moisture makes it better than ground rods where the
soil may be dry.
The Polyphaser site has some articles on Ufer ground systems.
On single point grounding, you can have as many grounds as it is convenient to
have but you only want one lead connected to your equipment. If you have two
leads like the power ground lead and your installed ground lead connected to
your equipment you have created a ground loop. It is best to tie your installed
ground lead to the power ground at say the outlet where you plug the radio in.
It is still ok to tie them together at ground level too. The key is no loop
through the equipment.
73
Gary K4FMX
kb4tcu wrote:
> The ground you put in the concrete i.e. the rebar would not be optimum.
> Concrete is a very good insulator. The common 8' copper clad steel grd rod
> is hard to beat. "The more the merry" . also single point ground system.
> Try to get the neutral in your panel box at near the same potential. Plug a
> one wire connector to the ground connector of a outlet an connect it to your
> station ground wire. You do not want different potentials during a lightning
> strike. Imagine you were standing five feet from a tree that is about to
> get a direct lightning hit. If you had your feet 20 or thirty inches apart
> the voltage at you left foot would or might be 100,000 volts as the current
> dissipates the father it gets from the tree your right foot may have a
> potential of 30,000 volts the difference is 70,000 volts that would blow
> thru a pair of nike tennis shoes and you with not much problem. If your
> station is plugged into a grounded outlet that runs 100' to your service
> entrance and you have a separate ground rod out your window and a 10' wire
> there will be difference in potentials . REMEMBER SINGLE POINT GROUND
>
> ----- Original Message -----
> From: "Geo Clute W7LFD" <gclute@attbi.com>
> To: "AMPS" <AMPS@contesting.com>
> Sent: Monday, April 15, 2002 5:28 PM
> Subject: RE: [Amps] RF Ground for 2nd Floor
>
> > http://www.polyphaser.com/datasheets/PTD1016.pdf This seems to be a very
> accurate and valid discussion of grounding and protection from lightning
> strikes.
> >
> > Here, on the second floor of a tri-level house my office, radio shack is
> above the ground about 12 foot to the office 2nd floor. Below me is the
> garage. Located below the office floor about 4 ft and to the right about 1
> foot is the 250 amp electrical panel. I drilled through the floor and ran 6
> gauge insulated solid copper thru the panel to the outside. Then followed
> the electrical panel ground to the utility company's ground rod. Clamped
> and soldered. I ran 220 line from the panel up through the same opening.
> Then poured a 6 inch thick concrete pad at the side of the house (40'X12')
> and tied the ground rod to the rebar in several places.
> >
> > Not certain this is right, however it seems to work for the last 26 years.
> For VHF work I'm not sure anything this far away from ground will work
> properly.
> >
> >
> > Geo W7LFD
> >
> > Kim writes:
> > But, how best should I handle a station that's up in the air with no hope
> of a ground run short enough to constitute a good RF ground?
> >
> > _
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
> >
>
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