Contact Resistance Measurement

In circuit breaker contact resistance testing, the measured resistance is extremely small. When DC current is injected into a circuit breaker, the resulting voltage drop is typically only a few tens of millivolts.
At this signal level, the measurement method becomes critical.
If voltage is not measured differentially, significant errors can occur.
Vebko devices perform true differential voltage measurement, calculating the actual voltage difference across the breaker terminals rather than measuring with respect to ground.
However, measurement accuracy is not only about the method.
The connection between breaker terminals and measurement inputs can form a large loop area, allowing environmental noise to induce unwanted voltage and distort results.
To minimize this effect:
🛠️ Use twisted voltage measurement leads
⚡ Keep current injection cables separated from voltage measurement cables
📊 Review the voltage-versus-time curve after the test

In AMPRO, the breaker voltage waveform can be observed directly.
If noise is present, abnormal fluctuations will appear in the graph.
Another practical way to verify measurement accuracy is simple:
Repeat the test and confirm consistent results.
Stable and repeatable measurements indicate proper wiring, accurate differential reading, and minimal noise influence.

Designed for real-world protection testing