Wiring 10 — Industrial Ethernet (EtherNet/IP) Star Topology

Industrial Ethernet (EtherNet/IP) Star Topology

Why Industrial Ethernet?

Traditional fieldbuses — RS-485 Modbus, PROFIBUS, DeviceNet — were designed when 9600 bps was fast and network management tools barely existed. Industrial Ethernet replaces them with standard 100 Mbit/s (or 1 Gbit/s) TCP/IP infrastructure. That brings a critical advantage beyond raw speed: every device is reachable over IP. Commissioning tools, firmware update servers, SCADA systems, and MES databases all communicate on the same network without protocol gateways. EtherNet/IP, the industrial application layer used by Allen-Bradley and many others, runs implicit (cyclic I/O) and explicit (configuration and messaging) traffic side by side over standard Cat cable and managed switches.

Shielded Cabling in Industrial Cabinets

A VFD switching 15 kW at 4–16 kHz generates significant radiated and conducted electromagnetic interference. Standard unshielded Cat 6 cable — fine in an office — develops bit errors within metres of a VFD in a switchgear cabinet. Industrial Ethernet uses Cat 5e SF/UTP or S/FTP cables: a foil shield around each twisted pair plus an overall braided screen. The shield attenuates EMI by 30–40 dB across the frequency range of switching noise.

The shield must be connected to protective earth (PE) to be effective. However, it must be bonded at one end only — typically at the switch end, which is the central, well-earthed anchor of the star. Bonding both ends creates a ground loop: any earth-potential difference between two panels drives a circulating current down the shield braid, inducing the very noise you are trying to suppress. Each device's chassis also bonds to PE for touch-safety reasons, but that PE connection is made at the device itself, not via the cable shield.

Star Topology — One Cable per Device to the Switch

Every device connects directly to the managed switch with its own cable run. No daisy-chaining, no T-taps. This is the correct topology for EtherNet/IP star mode and is mandatory for switches that enforce STP/RSTP port states. The advantage over daisy-chain (ring) topologies is straightforward fault isolation: a cable fault or device failure brings down only that one link. The switch's port LEDs and built-in diagnostics immediately identify which device is offline without affecting any other device on the network.

Star vs Ring (DLR / MRP)

The RemoteIO block in this lesson has two Ethernet ports — ETH-IN and ETH-OUT — designed for ring topologies such as EtherNet/IP Device Level Ring (DLR) or PROFINET Media Redundancy Protocol (MRP). In a ring, the cable leaves the switch, daisy-chains through each remote I/O block using ETH-IN → ETH-OUT, and returns to a second switch port. If the cable is cut anywhere in the ring, the protocol detects the fault and switches traffic to the surviving path within milliseconds.

For this lesson, use only ETH-IN — the star connection. ETH-OUT is left unwired. This is the simpler, more common deployment in cabinets where the added complexity of ring management is not needed.

VFD Mains Feed

The VFD's three-phase mains input (L1, L2, L3) and motor output (U, V, W) live in a separate high-voltage cabinet section and are not shown on this canvas. What is wired here is the control-level Ethernet connection from the VFD's communication option module to the switch, and the VFD's PE chassis bond to the ground bar.