Industry standard for outdoor appliance AC input bulkhead connector
Why not IP67 rated IEC 60309?


IP44 250 VAC outlet and line-plug (see later for IP67 examples)
image©sjs77


  IEC 60309 (formerly IEC 309) is an international standard from the International Electrotechnical Commission (IEC) for "plugs, socket-outlets and couplers for industrial purposes".


...


  The colour of an IEC 60309 plug or socket indicates its voltage and frequency rating. The most widespread colours are yellow 125 V, blue 250 V and red 400 V. The black 500 V version can often be found on ships.




IP67 400VAC inlet and line-socket



IP67 120VAC inlet and line-socket.

(images from InternationalConfig)