The grounding system is the core barrier for electrical safety in fields such as power, communication, construction, and industry. The grounding resistance value directly affects the stability of equipment operation and personal safety. Accurately measuring the grounding resistance of the grounding device is a crucial step in evaluating the effectiveness of the grounding system and preventing electrical accidents. Grounding grid resistance testers, as specialized instruments for this task, are of vital importance for correct selection and proper use. This article will start from the technical principles and systematically explain the characteristics of two mainstream types of instruments, and provide targeted selection suggestions.
I. Instrument Classification and Technical Principles
Based on the test objects and working principles, the grounding resistance testers currently widely used in engineering are mainly divided into two categories. These two types of instruments have different application scenarios, working mechanisms, and technical performances. The specific characteristics are as follows:
(1) Large-scale Ground Grid Grounding Resistance Tester
This type of instrument is specifically used for measuring the overall power frequency grounding impedance of large-scale and complex grounding grids in scenarios such as substations, power plants, and communication hubs. It is a dedicated device for the acceptance and inspection of large grounding systems.
Test Principle
The equipment conducts testing operations based on the classic three-pole method or four-pole method. During the test, auxiliary current and voltage poles need to be set up in areas far from the measured ground grid. The instrument’s internal 45Hz/55Hz alternating current power supply is used to stably inject test current into the ground grid, accurately collecting loop voltage drop data, and finally calculating the grounding resistance value through the ratio of voltage drop to injected current. Technical advantages
The instrument is equipped with the core technologies of heterofrequency source and digital filtering, which can efficiently shield 50Hz industrial frequency interference and various harmonic interference in the field. Even in complex and strong electromagnetic environments, it can ensure the accuracy and repeatability of the measurement data. At the same time, the output current range of the equipment is 3A to 10A. The large current output feature can truly reflect the actual performance of grounding impedance under complex working conditions, which is in line with the actual operation of large grounding grids.
Typical measurement range and accuracy
The conventional measurement range is divided into two specifications: 0 to 15Ω and 0 to 200Ω. The accuracy grade can reach 1% to 3%, which can meet the high-precision detection requirements of large grounding grids.
(II) Clamp-type Ground Resistance Tester
This type of instrument is suitable for rapid detection of scenarios such as power poles, building grounding leads, and equipment independent grounding bodies. Its core advantage is the ability to perform online measurement without stopping or disconnecting the wires, which is suitable for routine and regular detection work.
Test principle
Based on the integrated structure of the clamp-type voltage coil, it forms a closed magnetic circuit with the measured grounding circuit. By applying an induced electromotive force to the circuit and simultaneously collecting the induced current generated by the circuit, combined with the principle of electromagnetic induction, the total resistance of the circuit is accurately calculated. The measurement result includes the resistance of the grounding body, the resistance of the lead-down line, and the contact resistance of each connection point. Technical advantages
The equipment does not require disconnecting the grounding lead wire or setting up auxiliary grounding stakes on-site. The testing operation is simple and the detection efficiency is high. It can achieve online measurement while the equipment is energized. It can precisely detect hidden faults such as rusting of the grounding lead wire, loosening of the bolts, and poor contact. It is suitable for high-frequency and wide-area inspection operations.
Typical measurement range and accuracy
The measurement range is wide, covering 0.01Ω to 1000Ω. The measurement accuracy is stable at ±1.5% to ±2%, meeting the routine detection standards for various small and medium-sized grounding bodies.
II. Key technical indicators and selection considerations
The selection of the grounding resistance tester should be determined by considering the scale of the tested grounding body, the on-site testing environment, the detection purpose, and the operational requirements. By combining the performance characteristics of the two types of instruments, the core selection basis and specification requirements are as follows:
(1) Adaptation to different field environments
The large-scale grounding resistance tester for large grounding grids features high precision and anti-interference detection, suitable for authoritative and high-precision detection scenarios such as engineering completion acceptance and annual preventive tests of large grounding grids, accurately reflecting the real grounding performance of large grounding grids.
The clamp-type grounding resistance tester features efficient and convenient detection, suitable for daily safety inspections, online fault troubleshooting, and multi-point batch rapid testing, focusing on regular status monitoring and hazard排查.
(2) Equipment performance characteristics
The core performance advantages of the large-scale grounding grid grounding resistance tester are strong anti-interference ability and accurate measurement results， which can truly reflect the grounding impedance characteristics under large current conditions； its shortcomings are that the testing process is cumbersome， requiring disconnecting the grounding lead wire and setting up wiring on-site， with a long overall testing period and inability to achieve rapid detection. The core assessment indicators are output current， frequency adjustment capability， range， and measurement accuracy. The output current directly determines the equipment’s load capacity and anti-interference level.
The core performance advantages of the clamp-type grounding resistance tester are no need to set up auxiliary grounding stakes， no need to disconnect the lead wire， convenient operation， and extremely high detection efficiency； its shortcomings are that it cannot measure the resistance of a single grounding body alone， and the measurement value is the comprehensive resistance of the entire grounding circuit， with slightly lower accuracy than the large-scale grounding grid tester. The core assessment indicators are clamp size， range， and loop resistance resolution. The clamp size determines the range of cable diameters the equipment can adapt to.
(3) Key selection decision points
1. Select based on the testing task. For high-precision and standardized detection tasks such as periodic verification of large grounding grids and engineering acceptance， prioritize the use of large-scale grounding grid grounding resistance testers equipped with multi-frequency anti-interference technology and with output current not lower than 3A， to ensure the authority and accuracy of the detection data. For daily inspections and hazard排查 of line poles， building grounding， and equipment lead-down lines， prioritize the use of clamp-type grounding resistance testers to improve detection efficiency.
2. Focus on verifying anti-interference capability. In scenarios such as substations and industrial plants with complex electromagnetic environments， there are strong power frequency interference and induced voltages. When selecting， pay special attention to the instrument’s power frequency suppression ability and anti-induction voltage performance. Instruments with multi-frequency testing technology can effectively adapt to strong interference testing scenarios， ensuring stable and reliable data.
3. Conduct pre-test calibration according to standards. Before using the large-scale grounding grid grounding resistance tester， it is necessary to conduct current and voltage test line conduction performance verification using a multimeter， and check the contact status of the auxiliary grounding stake and the soil to ensure good contact. Strictly follow wiring standards. The length of the current line should be 4 to 5 times the diagonal length of the tested grounding grid， and the length of the voltage line should be 0.618 times the diagonal length of the grounding grid. Avoid measurement errors caused by non-standard wiring.
4. Adhere to national standards and specifications. The selection and use of equipment must comply with corresponding metrological verification regulations to ensure the traceability of measurement values. Among them, the large-scale grounding resistance tester for the grounding grid must comply with the requirements of the JJG 1180-2021 regulation, and the clamp-type grounding resistance tester must meet the requirements of the JJG 1054-2009 regulation, ensuring that the inspection operations are compliant and the data is valid.
Post time: Jul-10-2026