Circuit breakers are important devices that interrupt current when an electrical fault occurs. If they fail to operate properly during a fault condition, the electrical system can be at risk of being damaged. Additionally, the mis-operation of such a device can lead to costly impacts associated with the interruption of electrical service. Technicians should regularly test for potential problems so the circuit breakers can be verified to operate according to their intended design. Regular maintenance practices provide the opportunity to identify and correct operational issues and ensure power system reliability.
After a number of operations, circuit breakers begin to collect carbonized contact materials that are a byproduct of arcing. This can be attributed to the point on the waveform at which current is interrupted in combination with the reactive characteristics of the circuit that it is being utilized to protect. There are circuit breakers that have circuitry to aid in the suppression of this resultant arcing. However, it isn't sufficient to eliminate carbon deposits on the contacts of these devices.
Circuit breaker testing and contact resistance measurements allow technicians to determine the degree to which pitting and carbon collection effect the integrity of the primary current path of a circuit breaker. The contacts should have a low resistance to current. However, surface area reduction (pitting), carbon deposits and other contaminants reduce the current carrying efficiency of the contacts. If not maintained, these types of issues will lead to excess heating and can prove to be detrimental to the electrical system which the circuit breaker is designed to protect.. A Digital Low Resistance Ohmmeter or DLRO is the tools used to measure the very low resistance of contacts.
Aside from resistance measurements, the characteristics of the circuit breaker can be analyzed using a circuit breaker test set. This tool helps detect mechanical and electrical problems in the circuit breaker.
Related electrical test equipment available for rent from Protec:
Editor’s Note: This post was originally published on June, 2014 and has been updated freshness, accuracy and comprehensiveness.