Re: ground rods

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

I think the "take home message" from the IEEE std is this:

1) What's close to the rod makes a heck of a lot more difference than what's
far.  25% of the resistance is in the first foot from the rod.
2) Don't put rods any closer together than one rod length, if your goal is
to reduce ground resistance (closer is ok if your goal is to reduce current
in each rod)
3) The diameter of the rod is unimportant
4) The type of soil is going to be the big requirement driver, both for the
diameter of  rod and the eventual resistance


I'm looking for some standards/data on RF grounds that takes into account
the EM properties.(specifically, skin effect)

Just for a ballpark... if your ground is, say 30 ohms, how does that compare
to the series impedance of your RLC secondary circuit..

Well.. if the total C is 60 pF, and you're running at 100 kHz, the Xc is
1/(2*pi*100E3*60E-12) = 1/ 37.7E-6 = (1/.377)E+4 = about 30,000 ohms.....

The ground resistance is insignificant..1/1000 th of the reactance..



----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, March 19, 2003 5:32 AM
Subject: RE: ground rods


 > Original poster: "Christopher \"CajunCoiler\" Mayeux by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <cajuncoiler-at-cox-dot-net>
 >
 >
 > Lots of good info there. Leaves me wondering if I should
 > try and memorize it, or just stick with my trusty copy
 > of the National Electrical Code... Article 250 covers a
 > lot of ground on grounding (pun intended).
 >
 >  > -----Original Message-----
 >  > From: Tesla list [mailto:tesla-at-pupman-dot-com]
 >  > Sent: Tuesday, March 18, 2003 6:07 PM
 >  > To: tesla-at-pupman-dot-com
 >  > Subject: ground rods
 >  >
 >  >
 >  > Original poster: "Jim Lux by way of Terry Fritz
 >  > <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>
 >  >
 >  > I've just put a web page up with some equations and tables for ground
 >  > rods.  They're taken from IEEE Std 142-1991: IEEE Recommended
 >  > Practice for
 >  > Grounding of Industrial and Commercial Power Systems.
 >  >
 >  > I haven't put the pretty diagrams in yet, but the tables and text
 >  > are there.
 >  >
 >  > http://home.earthlink-dot-net/~jimlux/hv/grounds.htm
 >  >
 >  >
 >  >
 >
 >