this is what i was thinking of.
View attachment 438299
Circuit breaker locks work similarly to those used on transformer-rectifiers. The lock is usually either a single one-tumbler lock or a single two-tumbler lock. At least one tumbler will be keyed the same as a lock on the corresponding transformer-rectifier ground switch. This key would be released from the circuit breaker only when the lock bolt was extended; thus assuring that power was turned off. The transformer-rectifier ground switch could then be "unlocked" and moved to the appropriate ground position. The two-tumbler lock is used when a panel switch lock is used on the transformer-rectifier control panel. The extra key is released when the lock bolt is retracted, the key released is used in the control panel switch lock which when turned to the proper position allows the controls to be switched on.