ISO 10924-2:2014

Overview

ISO 10924-2:2014 - Road vehicles - Circuit breakers - Part 2: User's guide is a practical guidance document for the selection and application of automotive circuit breakers. It explains the parameters and decision steps designers and technicians must consider when matching circuit breakers to vehicle electrical systems. The guide helps ensure reliable overload and short‑circuit protection while accounting for real‑world factors such as temperature, cable characteristics and device inrush.

Key Topics and Technical Requirements

• Scope and purpose: Guidance for choice and application of automotive circuit breakers; complements the test and definition requirements in ISO 10924‑1.
• Rated vs continuous current: Distinguishes the rated current (IR) used to identify a breaker from the continuous current (IC) a circuit can carry under specified conditions.
• Current, conductors and temperature: Relationship between current, conductor cross‑section, insulation, ambient temperature and time - affects cable heating and breaker sizing.
• Contact resistance and temperature rise: High terminal/contact resistance raises local temperature and may reduce allowable continuous current; temperature rise tests are recommended.
• Cable protection: Select breakers so they open before a cable reaches its maximum allowed temperature; illustrated correct/incorrect selection scenarios.
• Inrush withstand characteristics: Breakers must tolerate transient inrush currents (motors, capacitors) without nuisance trips; may require higher rated breakers if inrush energy is high or prolonged.
• Selectivity (coordination): Ensure upstream breakers do not trip when downstream protection operates - system hierarchy and time/current coordination.
• Voltage peaks on opening: Opening can produce voltage peaks (document notes peaks can reach up to about six times rated voltage) - consider insulation and transient suppression.
• Replacement and safety: Replacement must be done with circuits de‑energized.
• EMC: Circuit breakers as passive components generally do not require EMC testing per this guide.
• Annexes: Practical selection procedures (Annex A), selection examples (Annex B) and ambient temperature influence (Annex C).

Practical Applications and Who Uses This Standard

ISO 10924‑2:2014 is intended for:

• Automotive electrical system designers and engineers
• Component manufacturers (circuit breakers, connectors, cables)
• Vehicle integrators and harness designers
• Test engineers and maintenance technicians
• Procurement/specification authors

Use cases include sizing protection for wiring harnesses, selecting breakers for engine‑bay vs passenger‑compartment environments, coordinating multi‑level protection, and verifying behavior under inrush and thermal conditions.

Related Standards

• ISO 10924‑1 (Definitions and general test requirements)
• ISO 8820‑1 (Fuse‑links - Definitions and test requirements)
• ISO 16750‑1 and ISO 16750‑2 (Environmental conditions; electrical loads)
• Other parts of ISO 10924 (Forms and device types)

Keywords: ISO 10924-2:2014, automotive circuit breakers, road vehicles, circuit breaker selection, rated current, continuous current, inrush current, cable protection, selectivity, voltage peaks.