Understanding NEC Informative Annex G: Supervisory Control and Data Acquisition (SCADA)
Informative Annex G provides detailed guidelines for designing, implementing, and maintaining Supervisory Control and Data Acquisition (SCADA) systems used in Critical Operations Power Systems (COPS). These systems monitor and control critical electrical and mechanical utilities to ensure operational continuity during emergencies.
Scope of Annex G
This annex applies to SCADA systems used for managing mission-critical loads, including:
- Fire alarm systems.
- Power distribution and generation.
- HVAC and ventilation.
- Load shedding and fuel level monitoring.
Key Requirements for SCADA Systems
- General Requirements (A)
- The SCADA system must be separate from the building management system to ensure independence.
- Redundant systems (warm or hot standby) must prevent single-point failures.
- Open communication protocols (non-proprietary) must be used for interoperability.
- A programmable logic controller (PLC) is required as the system controller.
- The system must assess damage and determine integrity after an incident.
- Power Supply (B)
- Must use a dedicated DC station battery system (24–125 volts DC) with a 72-hour capacity.
- Listed surge protection devices (SPDs) must be installed to guard against power surges.
- Power supplies and batteries must be separate from other electrical systems.
- Security Against Hazards (C)
- Physical access must be restricted to authorized personnel.
- Enclosures must protect the system from dust, dirt, water, and other contaminants.
- The system must include fire protection via dry agents or preaction sprinkler systems.
- Connections to external networks must use encryption or fiber optics for security.
- Maintenance and Testing (D)
- Maintenance: Preventive maintenance programs must be documented, and systems should support concurrent maintenance without service interruptions.
- Testing: Systems must undergo periodic testing under actual or simulated conditions, adhering to manufacturer-recommended procedures.
Applications of SCADA Systems in COPS
- Operational Control
- Real-time monitoring and control of mission-critical utilities like power distribution and fuel levels.
- Enhanced Redundancy
- Backup systems ensure uninterrupted service during maintenance or failures.
- Cybersecurity
- Encryption and physical security measures protect against unauthorized access and cyber threats.
- Fire and Environmental Protection
- Advanced fire protection systems and robust enclosures reduce risks to SCADA hardware.
Conclusion
Informative Annex G emphasizes the importance of robust design, secure implementation, and rigorous maintenance for SCADA systems in Critical Operations Power Systems. These guidelines ensure reliable and secure operation of mission-critical facilities.
