UPR Series 16 Amp Plugs and Sockets are compact, lightweight, strong and corrosion resistant. They are used with portable or stationery electrical equipment in corrosive atmospheres and in Zone 1 and 2 and 21 and 22 installations. The UPR is designed with a mechanical interlock to insure disengagement cannot occur while energized. The same plug used in hazardous locations can also be safely used with interlocking non‑hazardous location receptacles.