You're right, Article 406 of the NEC doesn't specifically prohibit a receptacle inside a wall cavity with an access panel. However, there are several other factors to consider to ensure the installation is safe and code-compliant.Here's a breakdown of things to think about

Key Considerations and Potential Code Violations:
406.4 (D) Bathtub and Shower Space. While not directly applicable to a wall cavity, the spirit of this section is to prevent receptacles in areas prone to moisture. If there's any chance of moisture inside the wall (e.g., plumbing nearby, condensation), this could be a concern. 110.3(B) Installation and Use. Electrical equipment must be installed according to the instructions included in the listing or labeling. This often covers the type of enclosure and its suitability for the intended location. If the receptacle enclosure is not rated for "damp" or "wet" locations (if moisture is possible), this would be a violation. 314 Boxes, Conduit Bodies, and Fittings. Is the receptacle box properly secured and supported? Does the box provide sufficient volume for the conductors? Are the conductors entering the box properly protected (e.g., with cable clamps)? The depth of the receptacle inside the wall can cause some trouble here, because it may require excessive conductor length to connect. 314.17 (C) Cables and Connectors Entering Boxes and Conduit Bodies. The sheathing of the cable must extend at least 1/4" into the box. If the depth of the wall makes this hard to achieve, a non-compliant install may happen here. 314.23 Boxes and Conduit Bodies to Be Suitably Supported. The NEC requires the box to be properly secured. 110.12 Mechanical Execution of Work. This is the "workmanlike manner" clause. The installation must be neat and professional. Sloppy wiring, damaged conductors, or loose connections would be a violation. Future Accessibility and Maintenance

The access panel is key. The receptacle must be readily accessible for inspection, testing, and maintenance. If the access panel is difficult to remove, too small, or otherwise obstructs access to the receptacle, it's a problem. "Readily accessible" is a defined term in the NEC (Article 100), meaning "capable of being reached quickly for operation, renewal, or inspections without requiring those to whom ready access is requisite to climb over or remove obstacles or to resort to portable ladders, and so forth." Think about if you will need a special tool to access or if it can be easily accessed by most people.

406.9 Receptacles in Damp or Wet Locations. Make sure the receptacle is rated for the environment in which it is installed.

In summary

While not explicitly forbidden, a receptacle in a wall cavity requires careful consideration to ensure code compliance and safety. The key is proper installation, protection from moisture, and readily accessible access for maintenance.

Before proceeding


Inspect the wall cavity

Assess the potential for moisture, temperature extremes, and other environmental factors.2.

Choose appropriate materials

Select a receptacle, box, and wiring method suitable for the environment.3.

Ensure accessibility

Verify that the access panel is large enough and easily accessible for inspection and maintenance.4.

Follow all applicable NEC requirements: Pay close attention to grounding, box fill, conductor protection, and mechanical execution.If there's any doubt, consult a qualified electrician to ensure a safe and code-compliant installation. The small expense of having it done properly is well worth the money compared to the costs of an electrical fire, shock, or expensive repair. Flag for review