Interlock mechanism for explosion-proof fixture having circuit breaker switch

In an explosion-proof housing containing a plug receptacle for receiving a plug having a sidewall with an aperture therein, an electrical switch for completing or interrupting an electrical circuit to the plug receptacle, and switch operating means extending through the housing for actuation of the switch, an interlock means operably associated with the plug receptacle, comprising:

• (a) a safety shaft mounted in the housing and aligned with the aperture in the plug sidewall for movement normal to the plug sidewall between an engaged position and a standby position, said safety shaft comprising a shaft having a handle at a first end, a tip at a second end for engaging the plug sidewall aperture, and an annular groove thereon between the handle and the tip;
• (b) first means operatively connecting said safety shaft and the switch to prevent the switch from being moved between an energized position and a deenergized position unless said safety shaft engages the plug sidewall;
• (c) second means operatively connecting said safety shaft and the switch to prevent the plug from being inserted into or removed from the plug receptacle unless the switch is in the deenergized position;
• and
• (d) a locking pin for securing said safety shaft in the standby position until the plug is inserted into the plug receptacle, said locking pin being mounted in a sleeve in the housing normal to the longitudinal axis of said safety shaft and aligned with the annular groove of said safety shaft when it is in the standby position, a spring positioned between said locking pin and the housing biasing the locking pin into engagement with the annular groove of said safety shaft, said locking pin having integral triggering means connected thereto for moving it to a disengaged position when the plug is inserted into the plug receptacle.