Loop Resistance Tester, also known as Contact Resistance Tester or Micro-ohmmeter
is a specialized instrument used in power systems to measure the contact resistance of conductive circuits in high-voltage switchgear (such as circuit breakers, disconnectors, GIS, etc.). Its core function is to detect poor contact. In high-voltage and high-current environments, even an increase of a few micro-ohms (μΩ) in contact resistance can lead to severe heating, welding, or even explosion accidents. Therefore, it is a mandatory test item in preventive tests. The following is a detailed analysis based on 2025-2026 technical standards: 1. Core Working Principle: DC Voltage Drop Method This instrument strictly complies with IEC 62271 and GB/T 11022 standards, using the four-terminal connection method (Kelvin connection): Current terminals (I+, I-): Output a DC constant current source up to 100A, 200A, or even 600A, directly passing through the contact under test. Why high current? Small currents cannot break through the oxide film on the contact surface, resulting in falsely high resistance readings that do not reflect actual operating conditions (where large currents flow during operation). Only high currents can "burn through" the oxide layer and measure the true metallic contact resistance. Voltage terminals (U+, U-): Located inside the current injection points, they measure the voltage drop across the contact with high precision (
