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Detecting Circuit Breaker Contact Problems with Resistance Measurement

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Circuit breaker contacts are prone to degradation because they handle the main current of the electrical system. After a while of operation, the repeated interruption of large current causes arcing and carbon formation on the contacts. The carbon deposit increases the contact resistance and decreases its power delivery efficiency. This leads to heat dissipation on the contacts and may lead to eventual failure.


A Circuit breaker contact resistance measurement test allows technicians to spot problems early and prolong the operating life of the protective devices. Degraded contacts can cause overheating and weld the contacts together. This can be dangerous because it may not trip if an over current condition happens. To assess the condition of a circuit breaker’s contacts, a DLRO is often used to measure its resistance. An ordinary Ohmmeter cannot be used because the resistance of the contacts can range from 0.1 microOhms up to a few hundred microOhms. A microOhmmeter with a test current of at least 100 Amperes is optimal for most LV and MV power interrupters because it mimics the real-world operating conditions of circuit breakers.

Get the circuit breaker diagnostic equipment you need from Protec Equipment Resources. Our inventory carries circuit breaker timers, analyzers and other electrical test equipment to cater to your needs. Contact us today for more information on our the tools and our services.