On one of my recent projects, we ran into some issues with electromagnetic interference (EMI) on Ethernet network cables. The project included a 480 VAC motor control panel (MCP) with Ethernet-connected variable-frequency drives (VFDs).
Initially, all the motors and devices checked out without problems, but the team ran into network issues upon commissioning. With the help of our network engineers, it was determined that the Ethernet connection to the MCP was experiencing significant packet loss (lost messages) caused by EMI while the motors were running.
The team examined the MCP and found excess Ethernet cable routed through a 480 VAC wiring duct in the panel. By rerouting the cable to low-voltage duct and removing the excess cable, the team solved the communication problems.
With the proliferation of Ethernet-connected devices, it’s important to keep the following tips in mind to minimize the effects of EMI:
- Maintain at least a 2-inch separation between communication cables and Class 1 circuits (NEC 800.133).
- When crossing over AC circuits, cross at right angles.
- Use shielded cables and proper grounding connectors.
- Avoid excess cable for service loops.
With these tips in mind, you should be on your way to a noise-free Ethernet installation.
Evan Westra is an ICSI engineer with Interstates Control Systems Inc., a certified member of the Control System Integrators Association (CSIA). For more information about Interstates Control Systems, visit its profile on the Industrial Exchange.
