×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • 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!
  • Students Click Here

*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.

Students Click Here

Jobs

Earth surface potential and earthing electrode shape

Earth surface potential and earthing electrode shape

Earth surface potential and earthing electrode shape

(OP)
Hi,

I am trying to build small earthing electrode in very limited space for a house that doesn't have it. It will be used with RCD (deltaI 300mA or 100mA) in system with 240V. I am choosing between straight horizontal stripe (around 7 m long) and two horizontal stripes (3.5 m long) crossed at the center of each other at 90 degrees. It would be at 0.8 m deep. Calculated with formulas form this link: http://admin.copperalliance.eu/docs/librariesprovi... , formula number (7) it will be around 55 ohm with rho=300 ohmM. My question is how to minimize step potential voltage especially in longitudinal direction ? If I connect cable at the middle of the horizontal stripe would it be better to install vertical earth rods at the ends of the stripe 0.8 m deep to lower step potential in longitudinal direction or small V shape horizontal electrode. The same question is for two horizontal stripes crossed at the center of each other at 90 degrees.

RE: Earth surface potential and earthing electrode shape

If RCD will trip the supply within maximum 0.3 sec the Etouch50 –calculated according to IEEE 80/2000 ch. 8.3 -should be not more than 240 V-live to ground.
If two strips are employed- B as per Copper Table I for four-arm symmetrical-the electrode resistance will be only 34.8 ohm then the maximum trip time could be 0.5 sec.
However, in my opinion usually a RCD will trip in less than 0.1 sec.

RE: Earth surface potential and earthing electrode shape

(OP)
Does someone know formula for calculating earth surface potential for horizontal stripe earth electrode in longitudinal direction. I know how to calculate in transverse direction but I don't know how to calculate in longitudinal direction.

Is it safe to connect earthing electrode of the house with the earthing of the concrete utility pole that supports electrical wires (240V)?

RE: Earth surface potential and earthing electrode shape

In my opinion, the equipment grounding conductor [the grounded conductor installed in the load part of the utility supply disconnected means] has to be connected to a grounding electrode existing in the supplied installation perimeter. So, the pole stands outside of this perimeter in the supply side of the disconnected means. However, a bonding jumper has to be provided between both grounding conductors.
If the grounding electrode it is a water pipe or the grounding resistance is more than 25 ohm- according to NEC- a supplementary electrode is required.

RE: Earth surface potential and earthing electrode shape

hansforum,
If you are using 100mA RCCB for personal protection (normally should be 30mA), then why one should be worried about high step & touch potentials?
It looks like that you are following IEC60364 which allows a maximum touch voltage of 50V. That means the RCCB tripping current
multiplied by earth fault loop impedance = 50V. This earth fault loop impedance includes the earth (ground) electrode resistance
too. In other words, the usage of a RCCB allows you to have a fairly high electrode resistance, even you do not have to
measure it.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

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!


Resources