Abstract: A unitary line surge protector for removable connection to an individual, existing type-444 connecting block and jack assembly of a main distribution frame of a telephone exchange system at a telephone office or substation. Each connecting block and jack assembly includes a pair of normally closed jacks interposed between connecting lugs and a guide extension running generally parallel to the jacks. The line surge protector includes generally flat housing of electrically insulative material containing a pair of line surge protection devices. The housing has apertures that receive the jacks of the assembly, and interior contacts open the jacks and connect them through the protection devices. The dimensions of the housing are such that the protectors can be mounted adjacent one another both vertically and horizontally on a type-444 frame.