Ground Resistance Formula |
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| Symbol | English | Metric |
| \( GR \) = Ground Resistance | \(\Omega\) | \(\Omega\) |
| \( SR \) = Soil Resistance | \(\Omega\) | \(\Omega\) |
| \( L \) = Ground Rod Length | \(in\) | \(mm\) |
| \(\large{ \pi }\) = Pi | \(3.141 592 653 ...\) | \(3.141 592 653 ...\) |
| \( d \) = Ground Rod Diameter | \(in\) | \(mm\) |
Ground resistance, abbreviated as GR, also called earth resistance, is the resistance encountered by an electrical current when it travels from an electrical system or device to the Earth (ground) through a grounding electrode or system. It is used in the safety and functionality of electrical systems, particularly in the event of a fault or lightning strike, as grounding helps to protect equipment and people from electrical shock and damage.
Key Points about Ground Resistance
Grounding Electrode - This is a physical conductor (often a rod or a network of conductive materials) driven into the earth, which establishes a connection to the Earth for electrical systems.
Earth as a Conductor - The Earth can conduct electricity, though not perfectly. Ground resistance measures how easily electricity can flow into the Earth from the grounding electrode.
Measuring Ground Resistance - This is typically measured using a ground resistance tester or earth resistance meter. The ideal ground resistance is low, meaning the path for current to flow into the ground is easy. For most installations, a ground resistance below 5 ohms is considered acceptable, although this can vary by country or application.
Factors Affecting Ground Resistance
Soil Resistivity - Different types of soil (sand, clay, loam) have different capacities to conduct electricity.
Moisture Content - Wet soil has lower resistance than dry soil.
Temperature - Higher temperatures can increase resistance.
Electrode Size and Depth - Longer or more deeply buried grounding rods can lower ground resistance.
Importance of Low Ground Resistance
A low electrical ground resistance ensures that the system operates efficiently and safely, preventing dangerous voltage buildup.
Safety - In case of a fault (like a short circuit), excess current needs to be safely dissipated into the earth.
Equipment Protection - Low ground resistance helps prevent damage to electrical devices and systems by providing a low-impedance path for fault currents.
Lightning Protection - Grounding systems are essential for safely dissipating the energy from lightning strikes.
