INTERPLAY OF ENERGIES IN CIRCUIT-BREAKER AND FUSE COMBINATIONS

Some methods of product application in the circuit protection field ha ve not kept pace with the technological advances in the products thems elves. Assumptions that were valid a dozen years ago regarding the int eraction of the fuses and circuit breakers are no longer valid. These application methods, although they are not outdated when used as origi nally conceived, can today create potentially dangerous situations. Pe rformance criteria based on industry standards and verified through te sting is the common denominator the engineer uses to safely apply the products. This paper will review some of the contemporary operating pr inciples of molded-case circuit breakers and fuses. Emphasis is placed on energy levels. The paper will show how, in combination, these prod ucts and energies interact. This analysis of cause and effect will sho w why analytical selection of fuses for circuit breaker protection may yield unsafe combinations.