Overview
ISO 8056-2:1988 is an International Organization for Standardization (ISO) standard that defines general requirements and tests for terminations used on nickel‑chromium (Ni‑Cr) and nickel‑aluminium (Ni‑Al) thermocouple extension cables for aircraft. The standard covers the design, construction, crimping procedure and verification tests for non‑insulated crimp terminations (cosses / ferrules) applied to the standard flexible conductors of thermocouple extension cables so that thermoelectric integrity and constancy of resistance of the thermocouple circuit remain within specified limits.
Key topics and requirements
- Scope and definitions: Interaction of terminations, ferrules (frettage d’isolant), crimping tools, and positioners; maximum use temperatures linked to cable insulation groups (105 °C, 150 °C, 200 °C, 260 °C).
- Construction requirements: Materials must be Ni‑Cr or Ni‑Al with thermoelectric properties comparable to specified reference standards; termination geometry must allow correct conductor insertion and optional insulation ferrule formation.
- Crimping tools and positioners: Tools must control and permit inspection of crimp position, prevent premature release, and carry identification markings for traceability.
- Marking and documentation: Approved drawings must state dimensions, material, hardness, thermoelectric properties, compatible cable types and the marking code for the crimp tool/punch.
- Qualification and production tests:
- Qualification uses 16 samples (each sample: cable length with two identical terminations) with specified ambient test conditions (20 ±5 °C, ≤75% RH) and sequence of tests.
- Mechanical tensile (pull‑off) tests on samples (including thermal shock conditioning between 260 °C and ice water) with minimum pull‑off forces listed in the standard (Table 2) for different conductor sizes and materials.
- Visual inspection criteria (correct insertion of strands, absence of burrs, correct crimp form).
- Tool control and routine checks: Tools/punches must be checked before first use and periodically - e.g., every 3 months or every 1 000 crimps (per the standard’s guidance) - and inspected before use in production.
Applications
- Manufacture and assembly of aircraft thermocouple extension cables where reliable temperature measurement is critical (engine, environmental systems, sensors).
- Quality assurance and acceptance testing for crimped terminations ensuring consistent thermoelectric performance and mechanical integrity.
- Maintenance, repair and overhaul (MRO) activities requiring standardized terminations and verified crimp procedures.
Who should use this standard
- Aerospace cable manufacturers and suppliers
- Electrical and instrumentation engineers working on aircraft temperature measurement systems
- Quality, test laboratories and certification authorities
- MRO organizations and procurement teams specifying thermocouple extension cable assemblies
Related standards
- ISO 8056 (other parts): Part 1 (Conductors), Part 3 (Round crimp ferrules - dimensions), Part 4 (Butt‑splice crimp connectors - dimensions)
- ISO 1966 (crimped terminals for aircraft electrical cables) - referenced for ferrule testing and requirements
Keywords: ISO 8056-2:1988, aircraft thermocouple extension cables, nickel‑chromium, nickel‑aluminium, crimp terminations, crimping tools, tensile test, thermal cycling, insulation ferrule, aerospace cable standards.