IEC 60617 symbols: reading control diagrams
Industrial Control · Lesson 11 · Advanced
Purpose
Read IEC-style control documentation by resolving symbol meaning, device tags, terminal numbers, cross-references and defined normal state.
Learning objectives
- Read state and cross-references
- Separate standard control from safety functions
- Analyse faults and reset behavior
- Validate the complete input-logic-output path
IEC 60617 supplies graphical-symbol vocabulary, but a usable drawing also needs project conventions, reference designations, wire/terminal data and revision control.
Core theory
Read contacts in the device's defined de-energized/unactuated state. Follow device tags and cross-references to the coil or actuator that changes them.
Distinguish physical conductor connections from functional association, mechanically linked contacts, terminal strips, off-page references and cable cores.
Confirm the drawing legend and project standard: symbol appearance alone cannot establish voltage, rating, safety integrity or physical location.
| Term | Meaning | Symbol | Unit |
|---|---|---|---|
| Reference designation | Unique tag linking every representation of one device | Not applicable | Not applicable |
| Cross-reference | Pointer between related coil, contacts, page or location | Not applicable | Not applicable |
| Terminal number | Identifier for a physical connection point | Not applicable | Not applicable |
Assumptions: Symbols and terminal designations are defined by the supplied drawing set; Required safety performance comes from the machine risk assessment.
- Normal state: The drawing shows the de-energized state.
- Identify: 13-14 conventionally indicates a normally-open auxiliary, subject to the legend/product.
- Energize: When K1 operates normally, that contact closes; verify by exact device data.
Treat it as K1's NO auxiliary under the supplied convention, not as a permanently open switch.
Reasonableness check: The conclusion is checked across normal, demand, fault, reset and restart states rather than inferred from one component label.
- Reading a contact in the energized instead of defined normal state
- Using an ordinary PLC bit as an unvalidated safety function
- Assuming emergency stop isolates every energy source
Where this appears in practice
Clear diagrams and validated safety functions let competent people build, test, diagnose and modify machinery without losing the intended protective behavior.
Knowledge check
Does the drawn open state mean the contact stays open while its coil is energized?
No. Symbols normally show the defined de-energized/unactuated state.
Answer: No. Symbols normally show the defined de-energized/unactuated state.
Practical exercise
Trace every occurrence of three device tags across a supplied multi-page drawing and produce a terminal-to-terminal schedule.
Summary
- A diagram is a state model plus physical cross-reference
- Safety performance belongs to the complete function
- Stop, emergency stop and isolation are distinct
Sources and review
- IEC 60204-1:2016+AMD1:2021: Electrical equipment of machines: IEC; 6.1; International
- ISO 13849-1:2023: Safety-related parts of control systems: ISO; 2023; International
- IEC 62061:2021 with current amendments: Functional safety of machinery control systems: IEC; 2021; confirm current consolidated version; International
- IEC 61496-1:2020: Electro-sensitive protective equipment: IEC; 2020; International
- Electricity at Work Regulations 1989: UK Legislation; Current official text; Great Britain
Editorial review date: 2026-08-22. Professional electrical review is pending.