Junction Box Selection Guide
Configurations below are from the Turck Connectivity Part Number Key (B2401). Not every combination is offered in every style, so confirm the details on the product page.
| Port Connector |
Ports |
Signals per Port |
Homerun Options |
| M12 Eurofast | 4, 8 | 1 or 2; NAMUR versions for process sensors | M23 12- or 19-pin receptacle, Minifast 12- or 19-pin receptacle, terminal chamber (screw or spring clamp), or integral cable |
| M8 Picofast | 4, 8 | 1 (3-pin ports) or 2 (4-pin ports) | 8-pin or 12-pin M12 connector, or integral cable |
| 7/8" Minifast | Varies by style | Standard or series wiring | M23 12-pin, Minifast 3- to 12-pin receptacle, or integral cable |
| 1/2" Microfast | 4, 6, 8 | 1 | M23 12-pin or Minifast 6-pin receptacle, or integral cable |
Homerun Options
| Homerun Type |
When to Use It |
| Connector (M23 Multifast, Minifast, M12) | Swap the box without rewiring the panel. Order the mating homerun cordset separately from Cordsets. |
| Integral cable | One sealed assembly with the cable molded in, specified by length in the part number. |
| Terminal chamber (TB style) | Wire your own bulk cable into screw (SK) or spring clamp (FK) terminals through an M20 cable gland. |
Reading an M12 Multibox Part Number
Example: 8MB12-5P3-CS19.
| Code |
Meaning |
| 8 | Number of ports (4 or 8) |
| MB12 | Multibox with M12 Eurofast ports (12Z = low profile) |
| 5 | Port pin count (4 or 5) |
| P / N | PNP or NPN LEDs (blank = no LEDs) |
| 3 | LED count: 1 = power only, 2 = 1 signal LED per port, 3 = 2 signal LEDs per port, 4 = 2 signal and 2 power LEDs |
| CS19 | Homerun: 19-pin M23 male receptacle (CS12 = 12-pin, CSV = stainless, RSF 120/190 = Minifast, FK/SK = terminal chamber) |
Ordering Notes That Prevent Mistakes
- Match LEDs to your outputs: PNP (sourcing) LEDs will not indicate correctly with NPN (sinking) sensors, and the reverse. Choose P or N to match the devices.
- Count signals, not just devices: a 5-pin port can carry 2 signals, so an 8-port box can handle up to 16 inputs when each device uses both. Check that the homerun pin count covers every signal plus power.
- Order the homerun cable: boxes with a connector homerun need a mating cordset. Boxes with an integral cable do not.
- Cap unused ports: any open port breaks the seal. Add closure caps for ports you will not use.
- Drop cables: connect each device to the box with a double-ended cordset, or add a splitter to put two devices on one port.
Junction Box FAQ
What is a passive junction box?
A passive junction box collects the wiring from several sensors or actuators and routes every signal to one multi-conductor homerun cable back to the control panel. It contains no electronics or network interface, only wiring and optional status LEDs. Passive boxes cut panel wiring and make it faster to swap a failed device.
What is the difference between a passive junction box and an I/O module?
A passive junction box only consolidates wiring, so every signal still lands on an input card in the panel. An active I/O module converts the signals and communicates over a network such as EtherNet/IP or PROFINET, so only a network cable and power run back to the panel. Passive boxes suit machines that already have I/O capacity in the panel.
How many signals can one port carry?
On Turck M12 boxes, a 4-pin port carries 1 signal and a 5-pin port can carry 2 signals per port. On M8 boxes, 3-pin ports carry 1 signal and 4-pin ports carry 2. The homerun connector must have enough pins for all signals plus power and common.
Should I choose a connector homerun or an integral cable?
A connector homerun, such as a 12- or 19-pin M23 receptacle, lets you replace the box without disturbing the panel wiring, but you order the homerun cordset separately. An integral cable box ships as one sealed assembly at a fixed length. Terminal chamber boxes let you wire your own cable on site.
What does NAMUR mean on a junction box?
NAMUR junction boxes are wired for NAMUR sensors, a 2-wire standard common in process automation and intrinsically safe circuits. Turck offers NAMUR versions with common positive or isolated circuits and 1 or 2 signals per port. Use them only with NAMUR devices and amplifiers.
Need Help Laying Out a Junction Box System?
Tell us the number of devices, their connectors, and the signal count, and the Automation Distribution team will match the box, homerun, drop cables, and caps.
Contact Automation Distribution
