Expansion Type Circuit Protectors
Mx22 Series and MX23 Series
Principle of Operation
MX22 and MX23 Series Circuit Protectors uniquely differ in construction, performance and application from circuit protectors normally used for over-current component protection. This uniqueness is attributable to the use of two extremely thin, special alloy currentsensing strips which expand on overload, and an integral bi-stable over-center contact spring mechanism, ensuring performance characteristics unmatched by bi‑metallic protectors.
Referring to views 1 and 2 please note that load-sensing strips “A” are held in tension when unit is normally closed. Also note that over-center contact spring mechanism “B” exerts a force which assists the sensing strips in holding the contacts closed.
Under normal load conditions, and until current rises close to the trip point of the protector, the sensing strips’ tension and contact pressure are relatively constant.
When trip current level is reached, the sensing strips heat and expand rapidly, allowing the over-center contact spring mechanism “B” to relax, causing it to snap instantly into its reverse position and, in so doing, open the contacts. This is illustrated in views 3 and 4.
Conversely, just as the sensing strips heat very rapidly, they also cool very rapidly, allowing the protector to be reset immediately if desired.
Resetting the protector by pressing the reset button causes the over-center contact spring mechanism “B” to snap back to its normal operating position and reclose the contacts.
