The two major categories of circuit breakers are primary and secondary.  Primary breakers, not offered by Tyco Electronics, can be used alone and are rated to withstand relatively higher currents and short circuit values.  Secondary breakers, the type offered by Tyco Electronics, must be backed up by a branch circuit breaker or a fuse. They cannot be used without other appropriate circuit protection being in series with the secondary breaker. Secondary circuit breakers are also known by other names such as supplementary protectors or component protectors.