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#93065 - 04/30/05 10:33 PM Ground rods  
George Little  Offline
Joined: Jan 2004
Posts: 1,489
Michigan USA
Should the ground rod installed for lightning protection measure less than 25 ohms to ground?

[This message has been edited by George Little (edited 04-30-2005).]

George Little

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#93066 - 04/30/05 10:48 PM Re: Ground rods  
PCBelarge  Offline
Joined: Jun 2003
Posts: 681
Dobbs Ferry, NY, USA
That is a good question.I looked in a few of my resources and did not see any minimum value given as a point of reference.
I did see a minimum of an 8 ft ground rod that shall extend 10 feet vertically in the earth.

Pierre Belarge

#93067 - 05/01/05 12:53 AM Re: Ground rods  
Larry Fine  Offline
Joined: Feb 2005
Posts: 693
Richmond, VA
" 8 ft ground rod that shall extend 10 feet vertically..."

This I gotta see!

[This message has been edited by Larry Fine (edited 05-01-2005).]

Larry Fine
Fine Electric Co.

#93068 - 05/01/05 06:45 AM Re: Ground rods  
Roxie  Offline
Junior Member
Joined: Apr 2005
Posts: 6
simple, dig a hole 2 ft deep and drive the rod to the bottom, cover with dirt

#93069 - 05/01/05 09:51 AM Re: Ground rods  
Ron  Offline
Joined: Mar 2002
Posts: 582
White Plains, NY
Because that lightning protection ground rod gets bonded to the building's grounding electrode system, your results/regulation is by the NEC (more than one rod, no maximum resistance).
NFPA 780 doesn't have a maximum resistance established that I'm aware of.


#93070 - 05/01/05 09:53 AM Re: Ground rods  
PCBelarge  Offline
Joined: Jun 2003
Posts: 681
Dobbs Ferry, NY, USA
That is a requirement from NFPA 780-Standard for the Installation of Lightning Protection Systems.
3.13.1 &
Ths standard has an illustration that shows an 8' groundrod buried 2' to make up the 10' vertical burial depth.

I have seen this done many times, as it seems the big homes and larger office buildings are all installing lightning protection these days.

Pierre Belarge

#93071 - 05/01/05 12:08 PM Re: Ground rods  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,124
If you do a radio tower you will see guys who are serious about ground electrodes.
I inspected a bunch of Florida DOT "radio equipment shelters" (the little shack under the tower).
They use a Ufer, coupled to ground rods (up to 40') at the corners, a ground ring and buried radials out from there. Everything is cadwelded.

Greg Fretwell

#93072 - 05/01/05 12:14 PM Re: Ground rods  
iwire  Offline
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Greg don't you live in the lightning capitol of the world?

Bob Badger
Construction & Maintenance Electrician

#93073 - 05/01/05 05:52 PM Re: Ground rods  
Larry Fine  Offline
Joined: Feb 2005
Posts: 693
Richmond, VA
Yes, Roxie and PC, I knew that. It just struck me funny the way you (PC) worded it.

About two years ago, we did the ground work for a cellular phone tower. Rods every four feet along the ground ring, which was solid #2 tinned copper, and all spliced exothermically welded; all in a 2'+ ditch.

Larry Fine
Fine Electric Co.

#93074 - 05/02/05 11:25 AM Re: Ground rods  
HotLine1  Offline

Joined: Apr 2002
Posts: 6,872
Brick, NJ USA
Insight from another northern guy....what about a 10' x 3/4" rod????

BTW, anoyone ever install Lyncole Grounding devices?? Now that was a 'trip'!



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