Overview
EN 62808:2016 (identical to IEC 62808:2015) specifies requirements for the design, analysis and qualification of isolation devices used in nuclear power plant instrumentation and control (I&C) systems important to safety. The standard defines how to ensure electrical independence between redundant safety-system circuits and between safety and lower-class circuits, and provides guidance for determining the maximum credible fault used to set test levels for device qualification.
Key topics and requirements
- Scope and purpose
- Applies to isolation devices at power and signal interfaces where electrical independence is required.
- Focuses on verifying that faults in connected lower-class systems or redundant channels cannot prevent safety functions.
- Design requirements (Clause 6)
- Selection and application principles for isolation devices (circuit breakers, input current limiters, fuses, energy-limiting devices).
- Basic design rules, postulated faults and physical component arrangement to prevent common-cause failures.
- General principles (Clause 5)
- Definition of isolation characteristics and actuation priority to maintain safety function integrity.
- Qualification and testing (Clause 7)
- Requirements for test specification, environment and methods.
- Guidance on using the maximum credible fault as the basis for test levels and on testing energy-limiting devices.
- Documentation of test requirements and results for traceability and regulatory review.
- Fault analysis
- Guidance on determining the maximum credible fault and applying it to test-level selection (e.g., for EMC or electrical stress).
- Examples of device behaviour
- Treatment of circuit breakers tripped by fault currents vs. fault signals; application of fuses and current limiters.
Practical applications and users
- Who uses this standard
- Nuclear power plant operators (utilities), I&C designers, equipment vendors, systems evaluators and nuclear regulators.
- Where it’s applied
- Design and procurement of isolation devices for safety-grade I&C systems.
- Qualification testing programs to demonstrate isolation under credible fault conditions.
- Safety assessments where electrical separation between redundant trains or between safety and non-safety systems is required.
- Benefits
- Provides a structured method to demonstrate electrical independence and robustness of isolation devices against credible faults.
- Helps align device testing with appropriate test standards and regulatory expectations.
Related standards
EN 62808:2016 is essential for engineers and safety assessors involved in ensuring that isolation devices maintain the required electrical independence and resilience of nuclear I&C safety systems.