ISO 8820-2:2014

Overview

ISO 8820-2:2014 - "Road vehicles - Fuse-links - Part 2: User guidelines" provides practical guidance for selecting and applying automotive fuse-links defined in the ISO 8820 series. It is intended to be used together with the other parts of ISO 8820 and focuses on fuse-links intended primarily for electrical cable protection. (Use of ISO 8820 fuse‑links for direct component protection requires agreement between customer and supplier.)

Key topics and requirements

• Rated voltage vs system voltage: select a fuse rated above the vehicle nominal voltage to allow for overvoltage conditions.
• Rated current and continuous current: distinguishes fuse rated current (identification) from the actual continuous current in the circuit; continuous current must be lower than fuse rated current.
• Cold resistance: cold resistance affects voltage drop, power dissipation and time‑current behaviour; production spread leads to variation in fusing time and voltage drop.
• Time–current characteristics: match fuse time‑current curves to cable heating curves so the fuse opens before cable temperature limits are exceeded.
• Cable protection rules: guidance and charts (Annex B) for choosing fuse rating and cable cross‑section to ensure cables are protected under overcurrent conditions.
• Selectivity (discrimination): ensure higher‑level fuses do not trip when lower‑level fuses operate - maintain system hierarchy for fault isolation.
• Inrush and stall currents: account for device inrush energy and motor stall currents; select fuses that withstand inrush without nuisance opening.
• Voltage transients on opening: opening a fuse can produce high voltage peaks (document notes peaks may approach 10× rated voltage depending on circuit impedance).
• Connection/contact resistance and ambient temperature: terminal resistance, fuse holders, ambient conditions and installation orientation affect continuous current capability and temperature rises.
• Replacement safety: replacement of fuse‑links should be performed with the circuit de‑energised.
• EMC: electromagnetic compatibility testing for fuse-links is not required by this part.

Practical applications and users

ISO 8820-2 is aimed at:

• Automotive electrical/electronic engineers specifying protection for wiring harnesses
• Vehicle manufacturers (OEMs) and tier suppliers selecting fuses and fuse holders
• Fuse manufacturers and component suppliers providing product guidance
• Maintenance and service technicians who replace or audit vehicle fuses

Typical uses:

• Sizing fuse‑links to protect cables and prevent overheating
• Defining fuse selection rules for fuse boxes and power distribution
• Ensuring correct coordination/selectivity across multiple protection levels
• Validating fuse selection against inrush, ambient temperature and installation constraints

Related standards

Use ISO 8820-2 with the rest of ISO 8820 series, e.g.:

• ISO 8820-1 - Definitions and general test requirements (normative reference)
• ISO 8820-3…9 - Specific fuse types and test fixtures (blade, bolt-in, strip, high-voltage types, miniature types)

Keywords: ISO 8820-2:2014, fuse-links, automotive fuse-links, road vehicles, cable protection, time-current characteristics, rated current, cold resistance, inrush current, selectivity.