Overview
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 ensures electrical independence between redundant safety system circuits, and between safety and lower‑class circuits as required by IEC 60709. It also provides guidance on determining the maximum credible fault to define appropriate test levels (e.g., for testing based on IEC TS 61000-6-5 or IEC 62003).
Key topics and technical requirements
- Scope and purpose
- Applies to isolation devices on power and signal interfaces where connections could compromise independence of safety functions.
- Aimed at preventing faults in lower-class systems or redundant channels from impairing safety functions.
- Design requirements (Clause 6)
- Selection and application of suitable isolation devices, including power isolation and energy limiting devices.
- Consideration of postulated faults, physical component arrangement and basic design robustness.
- Requirement that isolation devices be designed to the standards of the higher‑class (protected) system.
- General principles (Clause 5)
- Definition of isolation characteristics and actuation priority to ensure correct sequencing and fail-safe behavior.
- Qualification testing (Clause 7)
- Specification of test methods, test environments and documentation of test requirements and results.
- Use of the maximum credible fault as the basis for establishing test levels and for application‑specific testing (isolation between safety and lower class circuits or between redundant safety circuits).
- Guidance on testing of energy limiting devices and demonstration of performance under postulated fault conditions.
Practical applications and users
- Who uses IEC 62808
- Nuclear power plant operators (utilities), I&C system and equipment designers, safety evaluators, and regulators.
- Typical applications
- Defining and qualifying isolation devices where signals or power must be shared or routed between redundant trains or between safety and non‑safety systems.
- Establishing test programs for qualification of circuit breakers, fuses, input current limiters and other isolation hardware used in safety I&C architectures.
- Benefits
- Supports reliable electrical independence, reduces risk of common‑cause or propagated faults, and provides a documented basis for regulatory acceptance.
Related standards
Keywords: IEC 62808, isolation devices, nuclear power plants, I&C systems important to safety, maximum credible fault, qualification testing, IEC 60709, electrical independence.