Overview
IEC 61605:2016 - "Fixed inductors for use in electronic and telecommunication equipment – Marking codes" - specifies standardized marking systems for fixed inductors used in electronics and telecom equipment. The third edition (2016) defines how inductance values, tolerances and manufacture dates are marked on components using colour bands, digit/letter codes and date-code schemes. A significant technical change in this edition is an updated date code system.
Key topics
- Colour code (Clause 3)
- Four-band colour coding is specified: the first two bands = significant figures, the third = multiplier, the fourth = tolerance. Colours correspond to digits, multipliers and common tolerance values (examples provided for 47 μH ±10 %, 4.7 μH ±2 % and 4.7 nH ±5 %).
- Digit and letter code for inductance values (Clause 4)
- A three-character system (digits + multiplier) for values ≥ 10 μH and alternate two-character forms (using letters R/N for µH/nH decimal point placement) for smaller values. Examples in the standard cover ranges from nH through henry.
- Tolerance letter codes (Clause 5)
- Letter codes identify symmetrical tolerances (Table 4). Where no code exists, letter “A” indicates tolerance is defined elsewhere.
- Date code systems (Clause 6)
- Several date-code options are given: single-character (four-year cycle), two-character (twenty-year/year+month), and four-character (year+week) formats. This edition updates the date-code system to improve traceability.
- General marking rules
- Placement, band order (first band nearest component end), and spacing rules are included to avoid misreading. The colour code aligns with values from IEC 60063 (E3–E24 series).
Applications and who uses it
IEC 61605:2016 is used by:
- Inductor manufacturers - for consistent product marking and avoiding misinterpretation on components.
- PCB assemblers and OEMs - to verify correct part selection and assembly.
- Procurement and inventory teams - for accurate part identification and stock control.
- Test labs and field technicians - to read values, tolerances and manufacture dates without equipment.
- Quality, traceability and failure analysis - date coding facilitates batch tracking and warranty/recall investigations.
Practical benefits include faster visual identification of inductance and tolerance, improved supply-chain traceability, and reduced assembly errors.
Related standards
- IEC 60063 - preferred numbers series (E3 to E24) referenced for colour code values.
- ISO 8601 - referenced for date/time representation where applicable.
- Prepared by IEC Technical Committee 51 (Magnetic components and ferrite materials).
Keywords: IEC 61605:2016, fixed inductors, marking codes, colour code, inductance values, tolerance codes, date code, component marking, inductor identification.
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