Jordresistansmätning

Jordresistansmätning, often referred to as earth resistance testing or grounding resistance measurement, is a critical electrical safety procedure. It involves measuring the resistance of the earth electrode system to the general mass of earth. This measurement is essential for ensuring that the grounding system can effectively dissipate fault currents and lightning strikes away from electrical equipment and people, thereby preventing electric shock and damage to property.

The most common method for jordresistansmätning is the fall-of-potential method, also known as the three-point or four-point method. This technique utilizes a specialized instrument called a earth resistance tester. The tester injects a known current into the earth electrode system and measures the voltage drop at different points. By applying Ohm's Law, the resistance can be calculated. Typically, the earth electrode being tested is connected to one terminal of the tester. Two additional stakes, a current electrode and a voltage electrode, are driven into the ground at specified distances from the main electrode and each other. The tester then measures the resistance by applying current through the current electrode and measuring the voltage at the voltage electrode.

Low earth resistance is crucial for the proper functioning of protective devices like circuit breakers and fuses. If a fault occurs, a low resistance path to earth allows a large fault current to flow, quickly tripping these protective devices. High earth resistance can impede this current flow, leading to prolonged fault conditions and increased risk. Regular jordresistansmätning is a vital part of electrical maintenance and is often mandated by electrical safety regulations and standards in various countries. The results of these measurements help determine if the grounding system is performing adequately or if remedial actions, such as improving soil conductivity or adding more electrodes, are necessary.