How to install a junction box - step by step

A junction box is where electrical wires in an installation are gathered and distributed. Correct installation is crucial for the safety and reliability of the entire electrical system. In this article, we will look at the types of boxes and how to install them correctly.

Types of Junction Boxes

Concealed box (for flush mounting)
Concealed boxes are flush-mounted in the wall—behind sockets, switches, or as standalone distribution points. They are made of plastic and are available in a round shape with a diameter of 60 or 68mm.

Typical applications:
- Under sockets and switches in brick walls
- Under sockets and switches in plasterboard
- As a distribution point for concealed wiring
- Connecting wires behind the wall

Surface-mounted junction box
Surface-mounted junction boxes are installed on the surface of a wall, ceiling, or outdoors. They are available with various degrees of protection (IP rating) depending on the installation environment.

Typical applications:
- Wire distribution for surface-mounted installations
- Installation in wet rooms (IP54 and higher)
- Outdoor installation (IP55, IP68)
- Industrial and commercial facilities

What does the IP rating mean?

The IP rating indicates the degree of protection of the box:
- IP54 — protection against dust and splashing water from any direction
- IP55 — protection against dust and water jets
- IP68 — complete protection against dust and continuous immersion in water

For dry indoor areas: IP40 is sufficient (protection against solid objects, no protection against dust).

For bathrooms and kitchens: minimum IP44.
For outdoors: minimum IP55.
For direct contact with water: IP68.

Installation of a concealed box — step by step

Step 1 — Turn off the power
Before working, turn off the main circuit breaker and check with a tester that there is no voltage.

Step 2 — Carve out the recess in the wall
Using a chisel or drill, carve out a round recess with a diameter slightly larger than the box. The depth should be such that the box fits flush with the wall surface.

Step 3 — Run the wires
Thread the wires through the side openings of the box before placing it in the wall.

Step 4 — Fix the box
Place the box in the recess and fix it with the expanding wings (for brick walls) or with screws (for plasterboard). The box must be stable and flush with the wall surface.

Step 5 — Connect the wires
Connect the wires with WAGO terminals or screw terminal blocks. The phase (brown/black), neutral (blue), and protective earth (yellow-green) must be connected correctly.

Step 6 — Close the box
Install the cover or mount the socket/switch on the box.

Installation of a surface-mounted junction box — step by step

Step 1 — Turn off the power
Turn off the main circuit breaker and check with a tester.

Step 2 — Choose a suitable location
The box must be accessible for future inspection and maintenance. Do not hide it behind furniture or under plaster without a cover.

Step 3 — Drill the cable entries
Drill out the knockouts on the periphery of the box only where cables enter. Use cable glands (PG or M-type) for sealing.

Step 4 — Fix the box to the wall
Drill holes, insert wall plugs, and fix the box with screws.

Step 5 — Insert the cables and connect
Insert the cables and connect them with terminals or WAGO connectors. Check each connection for tightness.

Step 6 — Close the cover
Close the cover and check the seal. For IP55 and higher, ensure the sealing ring is correctly placed.

Tips for correct installation

- Never overload the box — do not cram too many wires into a small box
- Use only terminals for connections — twisting and taping is not permissible
- Leave sufficient wire length in the box — a minimum of 10-15cm
- Mark the wires for easy future identification
- The box cover must always be in place — never leave a box exposed

See available concealed boxes in our store: 

See available surface-mounted junction boxes in our store: 

Important: Electrical installations must be performed by a qualified electrician. The information in this article is for educational purposes only.