Ground Rod Resistance Formula

R resistance p soil resistivity l length.

Ground rod resistance formula. L total length grounding grid conductors 4 x 200 6 x 150 6 x 50 2000 meters. You should measure the resistance of an electrode with respect to the surrounding soil in the area. R p 2 pi l ln 4l a 1 p 2 pi s 1 l squared 3s 10x8 2l 10 4 5s 10 4 where. For example the national electric code requires no greater than 25 ohms of resistance in a ground system.

In some instances ground rods can be installed in areas where the earth has a lot of resistance. You can only do this by using the fall of potential method with a three terminal earth ground resistance tester. Hi slamat thank you for your question regarding resistance to ground calculations for parallel electrodes it is our pleasure to help. ρ resistivity of soil ω meter l length of electrode meter d diameter of electrode meter example.

Ground ring ground rods. R ρ 2 3 14xl loge 8xl d 1 where. If this is the case for your ground rod the best solution is to drive a different rod into a different location. The simplified calculation for predicting the resistance to ground earth of a given length grounding rod is.

Multiple ground rods yield a lower resistance to ground than a single rod. P2 and c2 connect to a separate all metallic grounding point like a water pipe or building steel. The total burial length is the combination of the horizontal and vertical conductors in the grid as well as the ground rods. However we can estimate the resistance to ground using scenario b.

So if you are using 10 foot ground rods you must place. To properly test the resistance of a ges you must follow some simple rules. For instance if a ground rod is driven into a very rocky and dry area it may not conduct electricity into the ground well. Calculate the upper limit of ground resistance rg of the grid if soil resistivity is 180 ω m for a ground grid shown in below figure.

Step 1 connect your length of wire to a metal stake in the ground. Make sure that you have stripped back the insulation from both ends of the wire to allow for a good connection. R1 resistance of one ground rod n total rods in layout k combining factor rn total net resistance of grounding system r measured earth to ground resistance using ieee 4 point method p 38 30 r for 10 ground rods 19 15 r or 38 30 r for 20 ground rods k 378 log n 89. Use the above formula to approximate the ground resistance of a system and not as a replacement for actual ground measurements.

With this method the resistance of two electrodes in a series is measured by connecting the p1 and c1 terminals to the ground electrode under test. If your ground rods are placed at least one rod length apart you can use a formula to estimate the earth resistance of multiple grounding rods.