The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!


2017 NEC and Related
2017 NEC
Now Available!

Recent Posts
Parking lot pole light swap....
by gfretwell
10/24/16 08:46 PM
International Wire Colour Codes
by Tjia1981
10/23/16 12:08 PM
Son of Sparky
by HotLine1
10/20/16 07:43 PM
Speaking of Plugmold ...
by gfretwell
10/17/16 02:37 PM
Broken battery charger? Check for cobwebs!
by gfretwell
10/17/16 02:30 PM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
gfretwell 14
HotLine1 7
ghost307 7
renosteinke 6
Potseal 4
Who's Online
0 registered (), 268 Guests and 4 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#80186 - 03/14/02 10:09 AM # of Ground rods
AndrusT Offline

Registered: 03/14/02
Posts: 24
Whats the rule, on when you need to have 2 ground rods?
I have heard 2 reasons.
1. When the service is over 200 amps.
2. When your water pipe has a plastic main.

I have also heard the reason for this is cause you need 10 feet of ground (rod, or copper main) going into the earth. I can't seem to find this stuff myself. Thanks

2014 / 2011 NEC & Related Books and Study Guides
#80187 - 03/14/02 01:06 PM Re: # of Ground rods
Tom Offline

Registered: 01/01/01
Posts: 1069
Loc: Shinnston, WV USA
Unless you've got the $$$ for the tester & time to waste, you'll need 2 rods at all times.

See 250-56 1999 NEC
Few things are harder to put up with than the annoyance of a good example.

#80188 - 03/14/02 01:54 PM Re: # of Ground rods
sparky66wv Offline

Registered: 11/17/00
Posts: 2334
Loc: West Virginia
2002 NEC 250.56

A little more explanation:

Unless you have the equipment and time to prove that your one grounding electrode has a resistance of 25 Ohms or less (and the Power Company doesn't mind only one) then the NEC requires no less than two.

Ground Meggers are expensive...

Also, 250.52(A)(5) requires 8 ft to be in contact with the earth. 10 ft. could be your local PoCo requirement.

[This message has been edited by sparky66wv (edited 03-14-2002).]

#80189 - 03/14/02 04:34 PM Re: # of Ground rods
motor-T Offline

Registered: 11/10/01
Posts: 293
Loc: Girard, Ohio, USA
As it was explained to me by our inspector, he said, " Show me 25 ohms to ground, or drive two ground rods, its that simple."

#80190 - 03/14/02 07:09 PM Re: # of Ground rods
spkjpr Offline

Registered: 12/01/00
Posts: 226
Loc: Sedalia,MO, USA
Motor t, my inspector is even easier than that. He just says two ground rods no matter what.

#80191 - 03/22/02 02:48 AM Re: # of Ground rods
joeh20 Offline

Registered: 03/21/02
Posts: 95
Loc: Tullahoma, TN, 37388
Our local PoCo went behind their own office and drove 10 8' ground rods and never got 25 ohms. So they let us get by with two now. I worked on a 1200 amp 480v with 5 rods 10' apart cadwelded to 4/0 copper in addition to a clamp on a 4" galvanize water line thirty feet in direct contact with the earth and never got 25 ohms. But the key here was undisturbed earth, seems any fill really messes thing up.
Lighting the way

#80192 - 03/24/02 05:57 PM Re: # of Ground rods
NonLinearLoad Offline

Registered: 03/23/02
Posts: 56
Loc: McHenry, IL. USA
One rod as supplemental to primary ground as in city supplied water, attachment per code distances, service size to AWG sizing.
Got a well, TWO rods 6' apart all continous wire. Still it gets attached to the first copper accessible to tank as the backup water in the hole deal, got water it gets to the earth.
Wisconsin... TWO rods, due to soil.

#80193 - 04/02/02 03:56 PM Re: # of Ground rods
electricdiver Offline
Junior Member

Registered: 04/02/02
Posts: 2
Loc: howell,nj,usa
read 250-81 carefully. you don't need any grd rods if you meet the first several conditions

#80194 - 04/02/02 05:25 PM Re: # of Ground rods
electure Offline


Registered: 12/24/00
Posts: 4226
Loc: Fullerton, CA USA
All you really have to do is have less than 25 ohms to ground on your grounding electrode connection...if it takes 1 rod, or 100.
(rods are kind of a junky ground path. If you're in trouble, you can pour a concrete encased electrode aka:Ufer, by just putting 20' of GEC sized Cu wire in a trench filled with concrete. Unless you have some kind of "resistance dirt", it'll pass)


ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals