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#93065 - 04/30/05 07:33 PM Ground rods
George Little Offline
Member
Registered: 01/18/04
Posts: 1488
Loc: 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).]
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#93066 - 04/30/05 07:48 PM Re: Ground rods
PCBelarge Offline
Member
Registered: 06/08/03
Posts: 681
Loc: Dobbs Ferry, NY, USA
George
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.
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#93067 - 04/30/05 09:53 PM Re: Ground rods
Larry Fine Offline
Member
Registered: 02/18/05
Posts: 693
Loc: Richmond, VA
"...an 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).]
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Fine Electric Co.
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#93068 - 05/01/05 03:45 AM Re: Ground rods
Roxie Offline
Junior Member
Registered: 04/05/05
Posts: 6
simple, dig a hole 2 ft deep and drive the rod to the bottom, cover with dirt
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#93069 - 05/01/05 06:51 AM Re: Ground rods
Ron Offline
Member
Registered: 03/13/02
Posts: 582
Loc: 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.
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#93070 - 05/01/05 06:53 AM Re: Ground rods
PCBelarge Offline
Member
Registered: 06/08/03
Posts: 681
Loc: Dobbs Ferry, NY, USA
Larry
That is a requirement from NFPA 780-Standard for the Installation of Lightning Protection Systems.
3.13.1 & 3.13.1.1
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.
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#93071 - 05/01/05 09:08 AM Re: Ground rods
gfretwell Offline


Member
Registered: 07/20/04
Posts: 9039
Loc: Estero,Fl,usa
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.
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#93072 - 05/01/05 09:14 AM Re: Ground rods
iwire Offline
Moderator
Registered: 01/05/03
Posts: 4391
Loc: North Attleboro, MA USA
Greg don't you live in the lightning capitol of the world?
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Bob Badger
Construction & Maintenance Electrician
Massachusetts
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#93073 - 05/01/05 02:52 PM Re: Ground rods
Larry Fine Offline
Member
Registered: 02/18/05
Posts: 693
Loc: 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.
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Larry Fine
Fine Electric Co.
fineelectricco.com
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#93074 - 05/02/05 08:25 AM Re: Ground rods
HotLine1 Offline


Member
Registered: 04/03/02
Posts: 6778
Loc: 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'!

John
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