Specifically, outlines how to structure data exchange between a legacy relay interface and a new PLC. The practical utility here is the concept of the "black channel" —assuming the communication medium is unreliable and building safety logic on top of it using standardized function blocks (FBs) from Part 3. For an engineer in the field, this provides a ready-made checklist: define your fail-safe values, implement cyclic redundancy checks (CRCs) as per Annex B, and separate watchdog timers from application logic.
For professionals based in China, the mandatory and most relevant documents are not the Italian CEI 31-35, but the GB/T 16895 series of national standards. The Chinese standard (Low-voltage electrical installations – Part 1: Fundamental principles, assessment of general characteristics, definitions) is structurally equivalent and technically aligned with the international IEC 60364 series.
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The CEI is moving toward "smart standards." By 2026, expect the official CEI 31-35 PDF to include interactive decision trees and integrated ATEX declaration generators. This is another reason to avoid static, pirated PDFs—they will soon become engineering fossils.
Categories ranging from High, Medium, to Low, which heavily impact the final sizing of the hazardous boundary. Hazardous Zone Assignment For professionals based in China, the mandatory and
This appendix includes examples of hazardous area classification for typical industrial applications, such as:
: This specific designation could refer to a particular section or part within the CEI standards. For example, CEI 31-35 might relate to a specific type of electrical installation or equipment. The CEI is moving toward "smart standards
Standards are updated constantly. A PDF you find on a random file-sharing site (e.g., from 2008) is almost certainly obsolete . For example, recent amendments to Part 0 (General requirements) introduced changes to non-metallic enclosures and UV exposure testing. If you design a junction box using an old PDF, you will fail your ATEX certification audit. The cost of recertification far exceeds the price of the official document.
The 2019 update changed "Increased safety e" to "Ex eb" for specific sub-levels. Old PDFs lack this. Using an old standard means your equipment markings are legally non-compliant with current ATEX Directive.
Understanding CEI 31-35: A Comprehensive Guide to Hazardous Area Classification