Junction Box for PSU to Relay power cord

This printable box is designed to safely house four WAGO 221-412 connectors and create a clean, secure junction between a power supply unit (PSU) and a relay. It is ideal when you need to switch a PSU on/off via a relay while keeping all wiring protected, organized, and mechanically secured.

This case allows you to:

• Route two power cables (input + output)
• Connect all wires internally with 4× WAGO 221-412 connectors
• Secure the cables using printed cable glands
• Keep all junctions fully enclosed for safety
• Build a tidy relay-controlled PSU switching solution

Perfect for DIY electronics, LED power setups, smart home relays, bench power supplies, and general power-management projects.

To complete this build, you will need:

• 4 × WAGO 221-412 connectors
• 2 × M3 brass heat-inserts
• 2 × M3×8 mm trapezoidal head screws
• 3 × printed cable glands (from https://www.printables.com/model/114283-cable-gland-all-sizes/files):
  • 2 × D8_L10 cable gland + top and bottom nut
  • 1 × D7_L10 cable gland  + top and bottom nut

Assembly Instructions

• Print the enclosure (base + lid) and the required cable glands. I used ASA @0.2mm, 15% infill, no supports.
• Insert the M3 heat inserts into the lid and let them cool.
• Press the WAGO connectors into the wago holder.
• Assemble the top nut to the cable gland
  • ==> Watch out for the cable glands, they can be fragile and break. I put the top nut in place to avoid breaking it during mounting.
• Pass the cables through the cable glands, then into the box. 
• Strip the wires and connect everything using the WAGO 221  connectors.
• Tighten the cable glands for strain relief.
• Close the lid with 2 × M3×8 mm screws.
• Connect your relay inline with the PSU cable as needed.
• Everything stays clean, locked in place, and protected.

Wirring (EU):

• BLUE (Neutral)
  • Incoming BLUE → WAGO 1 → Outgoing BLUE
  • No relay involvement
• GREEN (Ground)
  • Incoming GREEN → WAGO 2 → Outgoing GREEN
  • No relay involvement
• BROWN (Live)
  • Incoming BROWN splits into two WAGOs:
    • WAGO 3: Incoming Live → Relay input WHITE
    • WAGO 4: Relay output BLACK→ Outgoing Live BROWN (PSU)