Can you put a junction box on the outside wall?

Quick Answer

Yes, it is generally permissible to install a junction box on an exterior wall as long as it meets certain code requirements. The main considerations are that the box must be weatherproof, properly secured, and easily accessible. Junction boxes on outside walls are common for outdoor lighting, receptacles, and other exterior electrical equipment.

Can You Mount a Junction Box Outside?

According to the National Electrical Code (NEC), junction boxes installed on exterior walls or in damp/wet locations must comply with the following:

• The box must be listed for use in wet locations (ex. weatherproof, raintight).
• Cables entering the box must be protected from moisture through the use of clamps, hubs, bushings, or other approved fittings.
• Any unused openings in the box must be closed with knockout seals, plugs, or other approved methods.
• The box must be mounted securely and in a readily accessible location.

As long as these provisions are met, it is generally permitted to install a junction box on an exterior wall of a home or building. The specific type of box required will depend on the location and application.

Types of Exterior Junction Boxes

Common types of exterior-rated junction boxes include:

• Weatherproof – For outdoor locations protected from direct exposure to rain, snow, or water spray. Must have a gasketed cover.
• Raintight – For wet locations with direct exposure to rain, snow, etc. Must have a gasketed, watertight cover.
• NEMA 3R – Enclosures constructed for either indoor or outdoor use to provide protection against falling rain and sleet. Must have knockouts filled.
• NEMA 4X – Watertight boxes for harsh outdoor conditions or hose down applications. Resistant to corrosion.

Metal or plastic boxes meeting these ratings are acceptable for outdoor installation on walls, eaves, or other external surfaces.

Installation Guidelines

When installing a junction box on an exterior wall, the following guidelines should be observed:

• Mount the box securely using corrosion-resistant screws or bolts through the back or sides of the box into solid framing.
• Position the box so that exposed conductors are protected and cable entries are pointed downward to prevent moisture ingress.
• Use appropriate clamps, hubs, bushings, or couplings for secure, weatherproof cable entry into the box.
• Seal the box interior and all unused openings thoroughly using listed compounds (ex. silicone or putty).
• Ensure the box remains accessible and is not blocked by insulation, vapor barriers, or other materials.
• Use only listed wiring methods from the box to maintain integrity against moisture (ex. THWN wire, liquidtight conduit).

Proper installation is critical to achieving a watertight, compliant junction box assembly on an exterior wall surface.

Junction Box Locations

Some common locations for exterior wall junction boxes include:

• At exterior receptacles, switches, or lights.
• For connecting low voltage landscape lighting cables.
• At the mounting location for illuminated address signs.
• Where exterior wiring routes transition from overhead to underground.
• For tapping into existing circuits to add outdoor outlets or fixtures.
• As pull points to facilitate wiring in outdoor conduit runs.

The junction box must be positioned in a conveniently accessible area at a height designated by local codes, while avoiding pathways, sprinklers, up-lighting, and other exterior design features. Extension rings can be used to recess a recessed box the desired distance from the wall face.

Conclusion

Yes, junction boxes can be installed on exterior walls as long as the proper weatherproof enclosure is used and code requirements for securing, positioning, sealing, and wiring the box are followed. By using boxes listed for wet locations and following the installation guidelines, exterior junction boxes can be safely and legally placed to facilitate outdoor electrical installations. A licensed electrician should be consulted for compliance with all local regulations.