Most homes have only a couple of outdoor outlets (electrical receptacles), but adding one can be easier than you might think. Instead of installing a new circuit for the outlet, you may be able to tap into an interior outlet on an existing circuit within the home. This is acceptable if the existing circuit can handle the additional power demand of the new outlet and it is a standard receptacle circuit. You cannot tap into bathroom or kitchen receptacle circuits or into dedicated circuits (those intended for a single appliance or other specific use).
The electrical box for the outdoor outlet must be waterproof and have a cover suitable for the location: If the outlet is protected from direct weather exposure, such as by a porch roof, it must have a weatherproof cover rated for damp locations; if the outlet is directly exposed to the weather and moisture, it must have an “in-use” cover rated for wet locations. Also, all outdoor outlets must have GFCI (ground-fault circuit-interrupter) protection. You can meet this requirement simply by installing a new GFCI outlet.
Note: The new circuit cable and GFCI receptacle must have the same amperage rating as the existing circuit. Use 12-gauge cable and a 20-amp receptacle for a 20-amp circuit; use 14-gauge cable and a 15-amp receptacle for a 15-amp circuit. (On residential installations, the National Electrical Code or NEC does allow 15-amp outlets to be used on 20-amp circuits.)
Source: The Spruce
