Milliohmmeters & Microohmmeters

Milliohmmeters and microohmmeters are specialized low-resistance measurement instruments designed to accurately measure resistances from a few microohms up to several kilohms, with emphasis on the sub-ohm range where standard DMMs lack the necessary resolution and accuracy. They use a four-wire (Kelvin) measurement technique to eliminate lead and contact resistance from the reading, ensuring accurate results on resistance values as low as 0.1 µΩ. These instruments are essential wherever the integrity of electrical connections, windings, or conductors must be verified to the highest standard — from routine asset maintenance to high-stakes acceptance testing.

Applications span transformer and motor winding tests, aerospace bonding verification, circuit breaker contact resistance checks, and power infrastructure maintenance. Field-grade instruments such as the Megger DLRO series support test currents up to 200 A to ensure accurate measurement of large cross-section conductors and low-resistance joints. Laboratory-grade microohmmeters from Keysight and Keithley serve precision R&D and component characterization where sub-microohm resolution is required.

Typical Applications

Transformer and motor winding resistance measurement for condition assessment
Contact resistance testing of circuit breakers, disconnectors, and bus bar joints
Bonding and grounding resistance verification in aerospace, defense, and rail
Cable and conductor resistance measurement for loss and integrity assessment
Lightning protection system continuity testing on wind turbines and tall structures
Precision component characterization in R&D and calibration laboratories

Popular Brands

Megger is the dominant field brand for digital low-resistance ohmmeters (DLRO), with the DLRO10 and DLRO100 series widely used in power and rail asset maintenance. Vanguard Instruments serves the transformer testing market. Keysight and Keithley provide laboratory-grade microohm measurement capability. Raytech and Cropico offer portable alternatives for substation and switchgear applications.