Smart questions
Smart answers
Smart people
Join Eng-Tips Forums
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Member Login




Remember Me
Forgot Password?
Join Us!

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips now!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

Join Eng-Tips
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.
Jobs from Indeed

Link To This Forum!

Partner Button
Add Stickiness To Your Site By Linking To This Professionally Managed Technical Forum.
Just copy and paste the
code below into your site.

bam55 (Electrical) (OP)
13 Jul 04 18:36
I have an application where I want to add concrete encased ground rods on the perimeter of my plant to reduce the copmbined ground resistance. The resistivity of the ground mat or grid conductors is high about 500ohm-m. The resistivity of the concrete encased electrodes will be assumed at 20ohm -m. So my ground rods now become 70ohms instead of around 300ohms. My question is : for the combined resistance in which I use to determine the GPR, I need to use a resistivity for the mutual ground resistance between the ground grid and rod bed. Do I use som,ething between 500ohm-m and 20ohm -m ? or is this not possible due to the inherent cabibility of the formula. The total grid area is about 16,000m2. The concrete foundation cannot be used because it is "insulated" by a vinyl linerunder the entire area. This can't be punctured.

Any good advice is welcome, however I am in a bit of a rush!

buzzp (Electrical)
15 Jul 04 0:12
I normally don't encourage cross posting but try posting this in the Power Engineering forum. You will have good luck there.
advidana (Electrical)
15 Jul 04 3:47
Why not connect you concrete incased wires to the pad ground grid, to elimate the step potenial.
HCBFlash (Electrical)
4 Aug 04 10:56
Something to consider also is that if the concrete encasements are exposed above the ground they will dry out in hot weather and the ground impedance will be affected.  I'm guessing that you already knew that tho...
HCBFlash (Electrical)
4 Aug 04 10:58
btw, could you share with us the formula you're using?
thanx
bam55 (Electrical) (OP)
7 Aug 04 8:45
The formula can be found in IEEE-80-2000 and actually it is too long to show in this format. I've tried to incorporate the concrete encased formula in the original formula and this seems to help but when there is frost I've concluded it won't help the resistance at all.

Since this time I've used a factor for frost that when applied shows I'm OK after all. This information can be found in CEA 249 D 541 (www.ceatech.ca). It was written by some authors of IEEE -80-2000 and gives a simplified version of the Schwarz with tables.

Regards

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close