Ground Resistance Test Voltage Ammeter Method Ratio Meter Bridge Method Electronic Performance Test

Ground resistance test/voltage ammeter method, ratio meter method and bridge method

Ground resistance is an important parameter used to measure whether the grounding condition is good. It is the resistance encountered when the current flows from the grounding device to the earth and then flows through the earth to another grounding body or spreads to a distance. It includes the grounding wire and the grounding body itself. Resistance, contact resistance between the ground body and the resistance of the earth, as well as the resistance of the earth between two ground bodies or the resistance of the earth from the ground body to infinity. The size of the ground resistance directly reflects the good degree of contact between the electrical device and the "ground", and also reflects the size of the ground network. The concept of ground resistance is only applicable to small ground grids; as the ground grid area increases and the soil resistivity decreases, the inductive component of ground impedance plays an increasingly important role, and large ground grids should adopt ground impedance design.

There are many factors that affect the grounding resistance: the size (length, thickness), shape, quantity, burial depth, surrounding geographical environment (such as flat land, ditches, and slopes are different) of the grounding electrode, soil moisture, texture, etc. In order to ensure good grounding of the equipment, it is essential to use an instrument to measure the ground resistance.

Ground resistance test requirements:
a. AC work is grounded, and the grounding resistance should not be greater than 4Ω;
b. Grounding for safe work, the grounding resistance should not be greater than 4Ω;
C. DC working grounding, the grounding resistance should be determined according to the specific requirements of the computer system;
d. The grounding resistance of the lightning protection ground should not be greater than 10Ω;
e. For shielded systems, if joint grounding is used, the grounding resistance should not be greater than 1Ω.

Test Methods

The measurement methods of ground resistance can be divided into: voltage ammeter method, ratio meter method and bridge method. According to the specific measuring instrument and the number of poles, it can be divided into: hand-operated ground resistance meter method, clamp ground resistance meter method, voltage and ammeter method, three-pole method and four-pole method.
When measuring ground resistance, some factors cause inaccurate ground resistance:
(1) The soil composition around the ground network is inconsistent, the geology is different, the density, dryness and wetness are different, and it is dispersed. The stray current on the ground surface, especially overhead ground wires, underground water pipes, cable jackets, etc., has a special impact on the test. big. Solution: Take measurements at different points and take the average.
(2) The direction of the test line is wrong and the distance is not long enough. Solution: Find the correct test direction and distance.
(3) The resistance of the auxiliary ground electrode is too large. Solution: Splash water on the ground pile or use resistance reducing agent to reduce the ground resistance of the current electrode.
(4) The contact resistance between the test clamp and the ground measurement point is too large. Solution: Polish the contact points with a file or sandpaper, and fully clamp the polished contacts with a test wire clamp.
(5) Interference effects. Solution: Adjust the pay-out direction and try to avoid the direction with large interference to reduce the jump in the instrument reading.
(6) Problems with instrument use. The battery is low, solution: replace the battery.
(7) The accuracy of the instrument decreases. Solution: Recalibrate to zero.
The accuracy of the ground resistance test value is one of the important factors in judging whether the grounding is good. Once the test value is inaccurate, it will either waste manpower and material resources (the measured value is too large), or it will cause safety hazards to the grounding equipment (the measured value is too small).