Rule 29 of 40 · Chapter V — Water, Weather, and Place
Treat wet locations as hostile
Why this rule exists
Water lowers everything that was protecting you. It drops skin resistance, bridges gaps that air kept open, corrodes connections into high-resistance faults, and gives current easy new paths to ground, through equipment and through you. A circuit that is benign in a dry room turns dangerous over a wet floor or a damp basement wall. That is why the code demands GFCI protection, weather-resistant devices, and specific enclosures wherever moisture is expected. Wet is not only standing water; humidity, condensation, and splash all count. Where water can reach the electricity, assume the danger is elevated.
In practice
In wet and damp locations, use GFCI protection, weather-resistant (WR) receptacles, in-use bubble covers outdoors, and enclosures rated for the exposure. Keep connections up out of where water collects, and route so water drips away from, not into, devices. Never handle electrical equipment with wet hands or while standing in water. Dry out damp equipment fully before energizing. In bathrooms, kitchens, pools, and outdoors, treat the whole area as a place where a fault will find water, and size your protection accordingly.
When it doesn't apply
Damp, wet, and dry are defined locations with different requirements; a covered porch is damp, an open deck is wet. Pools, spas, and fountains have their own extensive rules involving bonding grids and clearances; that work is specialized. If you are dealing with a pool or a permanently wet installation, bring in someone who does it regularly.