NJ, that is a good point. I installed one fusible double-throw switch in a service-entrance application in the 1970s to accommodate a standby genset. One set of fuses was normally hot through the utility feed [with the switch open.] At the time there was an NEC exception that clearly allowed the practice.
By job completion, a prominent label warned of the condition, and a piece of clear acrylic secured with non-metallic machine screws covered the {utility-powered} set of fuses.
