Littelfuse offers two types of fuses: chip fuses and telecom fuses. The chip fuses are constructed using a multilayer design, where the fuse element is completely enclosed inside a ceramic body. This construction is referred to as “solid matrix” and results in high reliability, improved in-rush (or surge) current handling and strong arc suppression characteristics. Chip fuses are used to provide overcurrent protection for systems using DC power sources. They are available in industry standard surface mount sizes and are mounted directly to a circuit board using standard processes. Chip fuses are available in two classifications, fast acting and slow blow, based on the time it takes for a given fault condition to melt the fuse element. The distinction between the two classes is governed by guidelines that are created by UL (Underwriter’s Laboratory). The FT600 telecom fuse uses a different construction referred to as wire-in-air, where the fuse element is suspended in air and then contained within the fuse body. This fuse is specifically designed to help telecom equipment manufacturers comply with North American overcurrent protection requirements.