A secondary disconnect assembly is for electrically connecting and disconnecting accessories to an electrical switching apparatus, such as a power circuit breaker. The secondary disconnect assembly includes a terminal block assembly comprising a mounting member, at least one terminal block removably mounted on the mounting member, and at least one accessory plug structured to be removably inserted into the terminal block to be electrically connected to the terminal block. The terminal block and the accessory plug each include a plurality of error-proofing features. The error-proofing features prohibit insertion of the accessory plug into the terminal block unless the accessory plug is correctly disposed in a predetermined orientation.