The core principle of the selection process is to ensure that the tester matches the testing requirements of the object being tested, while strictly complying with relevant safety regulations. During the selection process, the following six key factors need to be mainly considered:
1. Test Voltage
Test voltage is the primary consideration factor in the selection process. The selection is based on the rated working voltage of the tested cable: too low a voltage cannot effectively detect insulation defects, while too high a voltage may cause irreversible damage to the insulation layer.
The selection should follow the recommended requirements of relevant standards such as IEEE 43, and match the corresponding test voltage level according to the type of the tested cable:
100V – 250V: Suitable for communication lines, electronic circuits, and low-voltage control cables with a rated voltage of less than 100V
500V: Suitable for low-voltage power cables and related equipment in systems of 440V, 690V, etc.
1000V: Suitable for medium-voltage cables in systems of 3.3kV, 6.6kV, etc.
2500V – 5000V: Suitable for high-voltage cables in systems of 11kV, 33kV and above
During the selection process, it is necessary to prioritize choosing a tester with a test voltage range that covers the actual demand; if testing cables of multiple voltage levels is required, it is recommended to use a multi-range output tester, which can cover common ranges such as 250V, 500V, 1000V, 2500V, and 5000V.
2. Resistance Range (Measurement Range)
The insulation resistance value of cables varies greatly, and the measurement unit is usually in megohms (MΩ) or gigohms (GΩ). The basic principle of selection is: the resistance range must have sufficient width to accurately measure the extremely high insulation resistance of the cable under good conditions (in some scenarios, the resistance value can exceed 1GΩ or even 10GΩ), and also be able to accurately capture the low resistance values after the cable insulation deteriorates.
The typical upper range of modern digital insulation resistance testers can reach 1TΩ (1000GΩ) to 5TΩ. For most engineering and operation scenarios, a tester with an upper range of 1TΩ or 2TΩ can meet the usage requirements; the core is to ensure that the instrument has good measurement accuracy within the actual measured resistance range.
3. Accuracy
Measurement accuracy directly determines the reliability of the insulation resistance test results. The requirements for accuracy vary in different usage scenarios.
For routine scenarios such as engineering construction and daily equipment operation, a measurement accuracy of ±5% is a common and acceptable standard in the industry; for scenarios with higher data accuracy requirements such as laboratory testing and scientific research analysis, a ±3% or higher accuracy instrument can be selected.
4. Short Circuit Current
The short circuit current refers to the large current that the tester can output when measuring a low-resistance load. This indicator directly affects the stability of the test process and the anti-interference ability of the instrument.
The basic principle is: the larger the short circuit current, the stronger the test stability of the tester in scenarios prone to surface leakage current due to moisture or dirt, and the higher the speed and accuracy of the reading.
For long-distance cable testing or in humid working environments, it is recommended to use a tester with a short circuit current of ≥1mA. High-performance instruments can have a short circuit current of 3mA – 5mA.
5. Key Functions
The function configuration of the instrument must match the actual testing requirements. The core practical functions and applicable values are as follows:
Automatic calculation of polarization index (PI) and absorption ratio (DAR): As the core indicator for judging whether the equipment insulation is damp or aged, it is a necessary function for insulation testing of high-voltage power equipment.
Voltage Stabilization Function (GVG): Maintaining the output voltage stable during the test to ensure the accuracy of the measurement results.
Automatic Discharge Function: Automatically releasing the charge stored on the cable after the test to ensure personnel safety at the operation level.
Timer: Supporting 60 seconds, 10 minutes, etc. for timed tests to meet the time requirements of standardized testing procedures. Data Storage and Transmission: The test results can be stored and transmitted to the computer via USB, Bluetooth, etc., facilitating the generation of subsequent test reports and the analysis of insulation status trends.
Backlight Display Screen: It is suitable for working environments with dim lighting such as substations and basements, making it convenient for test personnel to read the data.
6. Portability and Power Supply
The insulation resistance tester is mainly used for on-site operations. When selecting it, attention should be paid to the portability and power supply configuration. Portable and battery-powered instruments should be preferred, while ensuring that the battery has sufficient battery life to meet the requirements of continuous on-site operations.
The current mainstream instrument types are mainly divided into two categories:
Hand-cranked Megohmmeter (Ammeter): It belongs to traditional testing instruments and has the advantages of durability and no need for external batteries, but it has the disadvantages of cumbersome operation, limited measurement accuracy, and single functionality.
Digital Megohmmeter: It is the current industry mainstream choice, with the advantages of simple operation, rich functions, high measurement accuracy, and complete safety protection features.
Post time: Jan-27-2026