Intelligent Power Today Magazine

Molded case circuit breakers (MCCBs) are critical components in electrical systems, providing protection by isolating circuits during overload or short-circuit conditions. However, as MCCBs age, their reliability can diminish, necessitating comprehensive diagnostics to assess their condition and determine whether refurbishment or replacement is the optimal solution.

Molded case circuit breakers, while robust, experience wear and age over their service life. Proactive assessment of their condition allows operators to make informed choices between refurbishment, replacement, or continued operation with close monitoring.

Diagnostic Techniques

• Visual Inspection: Closely examine for signs of excessive arcing on contacts, cracked or discolored insulation, loose connections, and any evidence of overheating or mechanical damage.
• Contact Resistance Measurement: Specialized instruments measure contact resistance in the closed position. Rising resistance indicates contact wear, while trending this value over time provides insights into degradation.
• Infrared Thermography: Under load, thermal imaging of an MCCB can detect hot spots at connections, on contacts, or within the trip unit, potentially signifying deterioration or developing issues.
• Trip Unit Testing: Dedicated test sets inject precise currents and measure trip times against the MCCB's time-current curve. This validates both the overload and short circuit tripping functionality of the breaker.

Refurbishment versus Replacement

Assessing Refurbishment Viability

Refurbishment...