1. Circuit interrupter apparatus, comprising: interrupter means for conducting current flow through an associated circuit and for operating to interrupt the current flow on command; sensing means for sensing current flow through said interrupter means; trip unit means connected between said sensing means and said interrupter means for comparing current flow through said interrupter means to a predetermined time-current trip characteristic and for operating said interrupter means when current flow therethrough exceeds said time-current trip characteristic, said trip unit being operable to execute any of a plurality of optional functions; and a designator circuit comprising a plurality of selectable electrical connections, each pattern of said connections representing a discrete set of said optional functions; said trip unit means comprising interpretive means connected to said designator circuit for decoding the pattern of connections selected in said designator circuit and for commanding execution of the discrete set of optional functions represented by said pattern of connections.