What Is a Cartridge Fuse? - thespruce Many older electrical systems with fuse boxes (as opposed to modern breaker boxes) have two or more fuse blocks, each containing two cartridge fuses. One of the fuse blocks is the main fuse. This is the OCPD for the entire fuse box and thus all the branch circuits in the house. Cartridge Fuses at Lowes Shop Cartridge fuses in the circuit breakers, breaker boxes & fuses section of Lowes. Find quality fuses online or in store.