The ground resistance measuring instrument consists of a self-provided 110-115Hz AC power supply (hand-cranked generator or electronic power supply) and a potentiometer-type measuring mechanism. The main accessories of the ground resistance measuring instrument are three measuring wires and two measuring electrodes. The ground resistance measuring instrument has four connection terminals C2, P2, P1, and C1 or three connection terminals E, P, and C. During measurement, current and voltage electrodes should be driven into the ground at a certain distance from the measured grounding body; connect the C2 and P2 terminals (or the E terminal) to the measured grounding body, connect the P1 terminal (or P terminal) to the voltage electrode, and connect the C1 terminal (or C terminal) to the current electrode.
(1) For grounding devices that are electrically connected to the distribution network, it is better to disconnect them from the distribution network before measurement to ensure the accuracy of the measurement and prevent the measurement power supply from being fed back to the distribution network and causing other hazards.
(2) The measurement leads should avoid being parallel to adjacent overhead lines to prevent the danger of induced voltage.
(3) The measurement distance should be appropriately selected to improve the accuracy of the measurement. For example, when the measuring electrodes are arranged in a straight line, for a single vertical grounding body or a combined grounding body with a small area, the distance between the current electrode and the measured grounding body can be taken as 40m, and the distance between the voltage electrode and the measured grounding body can be taken as 20m; for a network grounding body with a large area, the distance between the current electrode and the measured grounding body can be taken as 2 to 3 times the diagonal of the grounding network, and the distance between the voltage electrode and the measured grounding body can be taken as about 60% of the distance between the current electrode and the measured grounding body.
(4) The arrangement of the measuring electrodes should avoid being parallel to underground metal pipelines to ensure the authenticity of the measurement results.
(5) If the measured grounding resistance is very small and the measurement connection line is long, C1 and P2 should be separated, and the connecting wires should be led out and connected to the measured grounding body separately to reduce measurement errors.
(6) Generally, grounding resistance measurement should not be conducted in rainy weather; during thunderstorms, the grounding resistance of lightning protection devices should not be measured.
(7) After connecting the leads, place the instrument horizontally and select an appropriate range. Rotate the crank at a speed of about 120 r/min continuously or connect the power supply. At the same time, adjust the potentiometer knob until the pointer of the instrument stabilizes at the center position. Then, read the value from the scale and multiply it by the range to obtain the measured grounding resistance value.
Post time: Sep-04-2026