The ground resistance should be measured periodically. The grounding resistance is measured using a grounding resistance meter (see the figure below). The grounding resistance meter consists of a 110-115Hz AC source (hand-cranked generator or electronic power supply) and a potentiometer-type measuring mechanism. The main accessory of the grounding resistance meter is three measuring wires and two measuring electrodes. Grounding resistance measuring instrument has C2, P2, P1, C1 four terminals or E, P, C three terminals. During the measurement, the current and voltage poles are driven into the ground at a certain distance from the grounding body to be measured; the C2 and P2 ends are connected in parallel (or the E-side) is connected to the measured grounding body, and the P1 end (or P end) is Connect to the voltage pole and connect C1 (or C) to the current pole. External wiring during measurement

Measurement of grounding resistances should pay attention to the following issues:
(1) For a grounding device that is conductively connected to the distribution network, it is best to disconnect it from the distribution network before the measurement to ensure the accuracy of the measurement and to prevent measurement power from feeding back to the distribution network and causing other hazards.
(2) The measurement connection should avoid parallel with the adjacent overhead line and prevent the danger of induced voltage.
(3) The measurement distance should be selected properly to improve the accuracy of the measurement. If the measuring electrode is arranged linearly, for a single vertical grounding body or a combined grounding body with a small footprint, the distance between the current pole and the measured grounding body may be taken as 40m, and the distance between the voltage pole and the measured grounding body may be taken as 20m; For a networked grounding body with a large area, the distance between the current pole and the measured grounding body can be taken as 2 to 3 times the diagonal of the grounding grid, and the distance between the voltage pole and the measured grounding body can be taken as the current pole. About 60% of the distance from the ground body to be measured.
(4) The arrangement of the measuring electrodes should be avoided in parallel with the underground metal pipes to ensure the authenticity of the measurement results.
(5) If the grounding resistance under test is very small and the measuring connection is long, separate C1 and P2 and lead the connection wires to the grounding body to be measured, so as to reduce the measurement error.
(6) The grounding resistance should not be measured on rainy days, and the grounding resistance of the lightning protection device must not be measured during a lightning storm.
(7) After the cable is connected, place the meter horizontally and select the appropriate magnification. Shake the crank or turn the power on and off at about 120r/min, and at the same time, adjust the potentiometer knob until the meter pointer stably points in the center When you are in position, you can read from the dial and multiply the reading by the override.