Model CH25SOL Interlock kit fits Eaton/Cutler Hammer Panels with a single, vertical-throw main breaker spaced at 2 1/4" from the top of the branch breaker stacks as shown.
 
In the "Normal" position, one or both of the main breaker and the solar breaker can be turned on and the gen breaker is locked out. In the "Gen On" position, the gen breaker may be turned on, but the main AND solar breakers are BOTH locked out.