Abstract: Disclosed is a mechanical interlock assembly for use within an electronics enclosure for preventing actuation of a service breaker switch when a main breaker switch is actuated. The mechanical interlock assembly comprises a bracket, an arm and a spring. The arm and spring are retained in a bracket which is mountable within the electronics enclosure adjacent the service breaker switch and the main breaker switch to selectively prevent unwanted actuation of the switches. The arm is slidable along a pin which extends between a first and a second side wall of the bracket. The spring is retained along the pin between the arm and the first side wall of the bracket, and the spring loads a force between the arm and the first side wall of the bracket when the arm is displaced along the pin. The spring presses the arm against a toggle lever of the service breaker switch after the arm has been been displaced and the toggle lever of the service breaker switch has been actuated.