ISO 8668-4:1993

Overview - ISO 8668-4:1993 (Aircraft terminal junction systems, Type 2)

ISO 8668-4:1993 is the International Standard that specifies the detail requirements for a type 2 Terminal Junction System (TJS) used in aircraft electrical installations. It defines the system’s intended operating temperature range (-55 °C to +155 °C) and the precise mechanical and electrical building blocks of the TJS: module families, frame types, spacers, removable male crimp contacts and sealing plugs. The standard ensures consistent dimensions, designations and markings so components from different manufacturers remain interchangeable in aerospace applications.

Key topics and technical requirements

• System scope and environmental range: Type 2 TJS designed for extreme aircraft temperature environments (–55 °C to +155 °C).
• Module types and sizes: Defines feedback modules (code 1) and feedthrough modules (code 2) in four sizes (A, B, C, D) with detailed dimensional drawings and tolerances.
• Frames and configurations: Specifies monolithic frames and double frames adapted to the module sizes, including length codes, fixing options and surface protection (anodic oxidation color codes).
• Spacers: Removable spacers (codes ER, ET) to adapt stacked-module lengths where needed.
• Contacts and sealing: Removable male crimp contacts in sizes 22, 20, 16, 12 with crimp-shank details and dimensional tables; sealing plugs for unused cavities with color and size coding.
• Designation and marking: Standardized part-designation rules (module/frame/contact/sealing plug codes) and marking of interconnection diagrams on the contact access face for traceability.
• Detailed drawings and tolerances: Includes first-angle projection drawings, dimensions in millimetres (plus inches where provided), assembly diagrams and interconnection diagrams.
• Referenced documents: Normative links to ISO 8668‑1 (characteristics), ISO 8668‑2 (tests) and tool specifications (e.g., MIL-I-81969 for installation/removal tools).

Applications and practical value

• Ensures interoperability and interchangeability of terminal junction components across aircraft harnesses and avionics.
• Used in design and manufacturing of aircraft electrical junctions, harness panels, connectorized assemblies and avionics backplanes where rugged, temperature‑resistant junction systems are required.
• Supports maintenance, repair and overhaul (MRO) by standardizing contacts, sealing plugs and frame assemblies to simplify spares management.
• Helps OEMs and suppliers achieve consistent mechanical fit, sealing and fluid resistance (codes for resistance to turbine oils/kerosene).

Who should use this standard

• Aerospace electrical engineers and harness designers
• Connector and TJS manufacturers and suppliers
• Avionics systems integrators and OEMs
• Certification bodies, procurement specialists and maintenance organizations
• Test laboratories assessing compliance with ISO 8668 family requirements

Related standards

• ISO 8668-1:1986 - Aircraft - Terminal junction systems - Characteristics
• ISO 8668-2:1986 - Aircraft - Terminal junction systems - Tests
• MIL-I-81969 (installation/removal tool specification) - referenced for tool requirements

Keywords: ISO 8668-4, terminal junction systems, TJS, aircraft connectors, feedback modules, feedthrough modules, crimp contacts, sealing plugs, aerospace electrical connectors, aircraft wiring harness.