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Here we see a violation of 404.4, which says, "A surface-mounted switch or circuit breaker in a damp or wet location shall be enclosed in a weather proof enclosure or cabinet that shall comply with 312.2. A flush-mounted switch or circuit breaker in damp or wet location shall be equipped with a weatherproof cover. Switches shall not be installed within wet locations in tub or shower spaces unless installed as part of a listed tub or shower assembly."
Although not completely clear in the photo, this switch is installed on a porch at the front door of a residential residence. In the 2005 edition of the NEC (and previous editions), Sec. 404.4 only addressed installations in "wet locations." So, for installations completed under the jurisdiction of the 2005 Code — which is still the case in some jurisdictions — it would be permissible to mount this switch without any type of weatherproof cover or box because this would be considered a "damp location." However, changes in the wording of this rule in the 2008 Code now make this type of installation a violation.
It should be noted that many installers would provide this switch with a weatherproof-while-in-use cover simply because they were concerned for safety and the long-term performance of switch, meaning many installers would exercise a bit of common sense and do more than the minimum required by the Code.