Reliability & Maintenance
Electrical system reliability in modern commercial and industrial environments is not a luxury, it is a requirement. And overcurrent protective devices play a major role in the reliability of these systems.
Modern current-limiting fuses operate by very simple, reliable principles. Fuses do not have to be maintained. By their inherent design, fuses do not have elements or mechanisms to calibrate, adjust or lubricate. If and when fuses are called upon to open on an overcurrent, installing the same type and amp rated fuses provide the circuit with new factory-calibrated protection. The original design integrity can be maintained throughout the life of the electrical system. See the pdf below titled Fuse Operation. One last point on fuse systems; the terminations, clips and disconnects should be maintained according to manufacturers recommendations.
In contrast, circuit breakers are mechanical devices (even those with electronic sensing) and circuit breakers require periodic maintenance, testing and, if necessary, reconditioning or replacement. This is required per the circuit breaker manufacturers' instructions, NFPA 70B Recommended Practice for Electrical Equipment Maintenance, and NEMA AB4. If circuit breakers are not properly maintained, the interrupting rating, circuit component protection, coordination and electrical safety may be compromised. See the Reliability and Maintenance paper below authored by Dennis K. Neitzel, Director, AVO Training Institute.
Understanding the operation of overcurrent protective devices such as fuses is critical to system reliability. This article discusses the basics of fuse operation.
Maintenance of Overcurrent Protective Devices
This paper written by Dennis K. Neitzel and others, explores failure statistics and reliability of overcurrent protective devices. This paper also contains recommendations for maintenance and testing.
Reliability & Selective Coordination
This paper addresses reliability as it specifically relates to selective coordination of the electrical system.