ECN Forum
Posted By: George Little Ground rods - 05/01/05 02:33 AM
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).]
Posted By: PCBelarge Re: Ground rods - 05/01/05 02:48 AM
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.
Posted By: Larry Fine Re: Ground rods - 05/01/05 04:53 AM
"...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).]
Posted By: Roxie Re: Ground rods - 05/01/05 10:45 AM
simple, dig a hole 2 ft deep and drive the rod to the bottom, cover with dirt
Posted By: Ron Re: Ground rods - 05/01/05 01:51 PM
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.
Posted By: PCBelarge Re: Ground rods - 05/01/05 01:53 PM
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.
Posted By: gfretwell Re: Ground rods - 05/01/05 04:08 PM
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.
Posted By: iwire Re: Ground rods - 05/01/05 04:14 PM
Greg don't you live in the lightning capitol of the world?
Posted By: Larry Fine Re: Ground rods - 05/01/05 09:52 PM
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.
Posted By: HotLine1 Re: Ground rods - 05/02/05 03:25 PM
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
Posted By: gfretwell Re: Ground rods - 05/02/05 04:45 PM
Yes Bob
It does get pretty "sparky" here in the summer ;-)
© ECN Electrical Forums