Abstract: The plastic material used to form the case and cover of a molded case circuit breaker includes a filler material such as glass fibers for strength purposes. To insure that the incoming plastic material contains the requisite filler material, a fluorescent material is included with the filler. Illumination of the plastic material under ultra-violet light confirms the presence of the fluorescent material and the filler material prior to fabrication of the circuit breaker case and cover. Illumination of the circuit breaker under ultra-violet light in the field confirms both the presence of the filler material as well as the source of manufacture.