An Intelligent Electronic Device (IED) is a field device used to monitor, protect, or control electrical equipment in substations and other operational technology (OT) environments. Examples include protective relays, meters, and bay controllers. IEDs can exchange measurements and commands with supervisory control and data acquisition (SCADA) systems and other devices.
IEDs matter in cyber security because they can influence physical processes, while their capabilities and operating constraints vary. Some may not support modern endpoint security or strong authentication. Attackers who gain access to an IED or its communications could potentially alter settings or disrupt operations. Defenders reduce risk through network segmentation, tightly controlled access, secure configuration and change management, and monitoring of device communications. Where an IED cannot support a direct control, compensating protections and residual risks should be documented.