Mechanical interlocks mount on surfaces and tap into existing power sources to provide safe electrical connections in outdoor and industrial applications. They are electrical devices with keyed pin/socket configurations that stop mismatched connections and have safety features that restrict power from flowing until the device is fully engaged to prevent electrical shocks and arcing. Their insulated constructions protect against impacts, keep out dust and debris, and have locking mechanisms that prevent unintended disconnections. Watertight mechanical interlocks protect against moisture and contaminant ingress and can operate in corrosive and wet environments. Hazardous-location mechanical interlocks have constructions that can be used in environments where flammable gases, liquids, flyings, and other combustible materials are present.