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Industrial DIN-Rail Smart 8-Port RS-485 Hub (FC-D8JM)

Name: Industrial RS485 Hub 8 Port
Brand: FCTEL

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Model FC-D8JM

Description :

FC-D8JM industrial DIN-rail smart eight-channel RS-485 hub. One master and eight independently isolated field ports, per-channel A–B short-circuit detection and automatic fault isolation, 3 kV isolation and up to 6 kV surge protection.

Overview

More than a splitter: protection for every RS-485 branch

The FC-D8JM industrial DIN-rail smart RS-485 hub distributes one upstream serial connection to eight field branches. The master port, eight downstream ports and power ground are isolated from one another. Each downstream channel has its own isolated 3 kV DC/DC supply, ground and shield connection, surge protection, status LED and A–B short-circuit detection. If one branch fails, the hub identifies and isolates that channel while the other seven remain available for communication.

1 + 8 master and field ports3 kV isolation per branch6 kV surge protection per RS-485 port7 healthy branches continue after one fault

FC-D8JM independent power and ground for each of eight RS-485 branches, with a fault isolated on channel 3 — Each field branch has a separate isolated supply and return path. A fault on one channel is confined to that port.

Independent isolation matters

Two hubs may both be described as “isolated” while using very different internal arrangements. In a shared architecture, several downstream ports can use a common isolated power supply and return path. A fault on one line may then affect other branches through that shared path. On the FC-D8JM, each of the eight field ports has its own isolated supply, ground and fault-handling circuit. The master-side ground is also separated from the downstream grounds. This helps reduce the effects of ground potential differences between buildings, workshops or equipment cabinets.

The comparison below explains the selection principle; it does not describe a particular competing manufacturer. Always confirm the isolation diagram and measured performance of a proposed model.

Typical shared-isolation hub architecture translated from the Chinese source diagram — Typical shared-isolation architecture. Compare its shared supply and return path with the FC-D8JM architecture shown above.

Find the failed branch at the cabinet

Stray copper strands at a terminal, moisture in a junction box, crushed insulation or a failed transceiver can short the A and B conductors. On a conventional shared bus, that may appear as timeouts across the entire network, leaving technicians to disconnect cables one by one. The FC-D8JM monitors the A/B condition of each field branch and also detects certain abnormal data conditions. It lights the corresponding channel indicator and isolates the affected line. Technicians can focus on an identified port while unaffected areas continue operating.

The hub also combines common-mode inductive differential filtering with FPGA digital filtering to reduce line spikes and high-frequency interference. Its FPGA logic produces RS-485 transmit/receive enable timing from the data being sent, supporting a range of baud rates and frame lengths. These functions are designed for industrial installations with many serial devices, long cable runs and challenging electrical environments.

Features

Functional features

One master, eight branches: one selectable RS-232/RS-422/RS-485 upstream interface and eight RS-485 downstream channels.
Per-port electrical separation: high-speed optocoupler signal isolation and an independent 3 kV isolated DC/DC supply for each downstream channel. The master and field-side grounds are separated.
Local fault containment: per-channel A–B short-circuit detection and data-error detection, automatic isolation of a faulty branch, and LED indication to identify the affected channel.
Surge protection: three-stage protection on each RS-485 port, rated to 6 kV under the stated test conditions; independent shield-ground connections are provided.
Filtering and timing: common-mode inductive differential filtering and FPGA digital filtering suppress transient noise; FPGA control generates transmit/receive enable signals.
Flexible installation: redundant dual DC 9–70 V inputs, overload and reverse-polarity protection, fanless heat dissipation, anodized aluminum enclosure, IP40 rating, and DIN-rail or wall mounting.
Industrial temperature range: –40 °C to +85 °C operating temperature.

Performance depends on cable quality, grounding, baud rate and installation conditions. Confirm the interface option and surge-test requirements for your project before ordering.

Specifications

Technical specifications

Model	FC-D8JM
Product type	Industrial DIN-rail smart eight-channel RS-485 hub with short-circuit detection and channel isolation
Serial ports	Eight RS-485 field ports; one selectable RS-232, RS-422 or RS-485 master interface
Serial standards	EIA/TIA-232 / ITU-T V.28; EIA/TIA-422 / ITU-T V.11; EIA/TIA-485
RS-485 wiring	Two-wire: A (TX+), B (TX–), GND. Four-wire RS-485 and RS-422: TxD+, TxD–, RxD+, RxD–
Isolation	3 kV electrical isolation; independent isolated DC/DC supply and ground for each downstream channel
Surge protection	Up to 6 kV on each RS-485 interface under the specified test conditions
Field nodes	Up to 128 enhanced-load nodes per RS-485 channel, subject to the electrical design of the installation
Transmission distance	Up to 2,200 m at 9,600 bit/s under the stated conditions
Power input	Redundant dual DC 9–70 V inputs; power consumption below 5 W; overload and reverse-polarity protection
Power connector	Four-position, 5.08 mm pitch pluggable terminal block
Housing	IP40 anodized aluminum alloy; fanless; DIN-rail or wall mounting
Dimensions and weight	110 × 86 × 40 mm; approximately 0.45 kg
Environment	Operating and storage: –40 °C to +85 °C; humidity: 0–95% RH, non-condensing
Reliability	MTBF >100,000 hours as stated by the manufacturer

For surge protection, the Chinese product page cites GB/T 17626.5 / IEC 61000-4-5 and a 10/700 μs test waveform. Confirm the test setup and required certification with FCTEL for your procurement specification.

LED status indicators

FC-D8JM LED indicator status table translated into English — Power and channel indicators from the original technical image.

Mechanical dimensions

Applications

One control link, eight protected field branches

Connect a PLC, controller or gateway to the master port and distribute its RS-485 connection to up to eight separately isolated areas. Typical endpoints include meters, access-control devices, variable-frequency drives and distributed controllers. Each branch can be monitored and maintained individually. If a short occurs on one line, the hub isolates that channel so the other connected areas can continue exchanging serial data.

Industrial application with one PLC master, eight independently isolated RS-485 branches and a detected fault on one field cable — Illustrative factory deployment. Final wiring, termination, grounding and communication settings should follow the site design.

Plan cable length, node loading, termination and grounding for each branch. The advertised distance and node count are maximum values under specific conditions; the usable limits for a site depend on baud rate, cable characteristics, electromagnetic interference and connected devices. Ask FCTEL to confirm the upstream interface option and protection requirements when selecting the hub.