| Home |
| Search |
| Today's Posts |
|
#9
July 11th 07, 01:54 AM
posted to rec.radio.amateur.antenna
|
|||
|
|||
Question on grounding rods
"Nick" wrote in message ... "Jim Lux" wrote in message ... wrote: John Doe wrote: Isn't concrete an insulator?? "The preferred ground in most jurisdictions is a concrete encased grounding electrode (aka a Ufer Ground, after the inventor's name Herb Ufer).. " What am I missing here? That while dry concrete is a pretty good insulator it is hard to find such just about anywhere other than Southern Arizona. And even there, the concrete is probably damper and a better conductor than the surrounding soil. Ufer's original work was developing grounding techniques for ammo bunkers in desert areas, since the ground rods didn't work. I, too, am amazed - I though concrete, whilst it would be damp on the outside underground bit, would be substantially dry after setting, and a good insulator, being essentially sand.. I guess its porous or microporous.. Nick Concrete never truly sets. The chemical reactions continue for centuries. Concrete structures put up 2000 years ago by the Romans are still perfectly useable today and under the surface remain chemically active. Many Roman structures such as the Colosseum and aquaducts would not have been possible without concrete. Some of the techniques developed then are still in use in building today such as making the higher levels of a structure using lighter, smaller aggregate. Embedding steel or copper rods in concrete will pretty much guarantee that the metalwork will remain in contact with moisture and conductive salts for as long as the structure holds together. The constant exposure to moisture and corrosive salts is the main reason for failure of modern ferro-concrete structures. Concrete will suck up whatever moisture is around, either from the air or the soil and is always damp inside, hence the steel rusting out unless protected by heavy galvanisation and sacrificial electrodes. Even in the worst environments, a couple of 8 foot copper rods embeded in concrete should give a DC or low frequency AC resistance/impedance of less than 200 ohms. Of course you could always use a dipole and balun. :-) Mike G0ULI |
| Thread Tools | Search this Thread |
| Display Modes | |
|
|
Similar Threads
|
||||
| Thread | Forum | |||
| Grounding Rods?? | Shortwave | |||
| Grounding question | Antenna | |||
| Grounding Question | Scanner | |||
| Grounding Question | Antenna | |||
| grounding question | Antenna | |||
Threaded Mode
