Glossary · Electrical engineering and control panels
Junction box
Also known as: Terminal box, Field junction box
German: Klemmenkasten
In electrical installation, a junction box is a small enclosure in the field in which cables from several devices are connected to terminals and combined into multicore cables leading to the control cabinet or I/O system.
- Control panels
In one sentence
A junction box is a field enclosure where device cables are terminated and combined into multicore cables to the cabinet.
Example
Eight valve positioners on a skid are wired to a junction box, from which one multicore cable runs to the marshalling cabinet.
How it applies
- Engineering: Junction boxes reduce cable lengths and enable modular skids. Select enclosure material, IP rating and, in hazardous areas, the correct protection type and certification. Remote I/O stations increasingly replace passive junction boxes.
- Installation: Keep intrinsically safe and non-intrinsically-safe circuits separated as the certification requires. Seal unused entries.
- Documentation: Terminal plans show each terminal with cable, core and device. The junction box tag must appear consistently in cable lists, loop diagrams and the box label.
- Maintenance: Moisture ingress and loose terminals in field boxes are common fault sources; inspection plans should include them.
Junction box vs. marshalling cabinet
A junction box collects field cables locally. A Marshalling cabinet sits near the control system and cross-connects field cables to system I/O. Both are defined by their terminal plans.