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.
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 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
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
RE: Earth surface potential and earthing electrode shape
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
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.