ISO 8668-3:1994

Overview

ISO 8668-3:1994 - "Aircraft - Terminal junction systems - Part 3: Detail specification for type 1 system" defines detailed characteristics for a Type 1 Terminal Junction System (TJS) intended for airborne use between −55 °C and +155 °C. It specifies the mechanical, electrical and identification elements that make up the TJS family: feedback and feedthrough modules, frames, clamps and inserts, removable ID tags, male crimp contacts (sizes 22, 20, 16, 12), and sealing plugs. The standard provides dimensional data (mm and inches), designation rules, interconnection diagrams and rated currents.

Key topics and requirements

• Scope & temperature range: Qualified for aviation applications from −55 °C to +155 °C.
• Modular components:
  • Feedback modules (code 1) and feedthrough modules (code 2) in four sizes (A, B, C, D).
  • Frames adapted to modules: Pl (standard), P2 (perforated), P3 (reinforced) for feedback; P4 for feedthrough.
  • Module clamps/inserts (SRI, SR2, ST1, ST2) and removable identification tags (5 × 2.8 × 0.5 mm, white background with red numbers).
• Contacts & wiring: Removable male crimp contacts in sizes 22, 20, 16, 12 with specified dimensional drawings and crimp shank details. Rated currents: size 22 = 5 A; size 20 = 7.5 A; size 16 = 13 A; size 12 = 23 A.
• Sealing plugs: Dimensioned, color-coded plugs mapped to contact cavity sizes (codes 01–04). Example: code 01 is used for size 22 cavities; codes 02, 03 and 04 correspond to other sizes (table indicates 02 = red, 03 = blue, 04 = yellow).
• Designation & interconnection: Formalized part-numbering and diagram codes (e.g., "ISO 8668-3 1 A 101 A") and printed interconnection diagrams on the contact access face for clear wiring identification.
• Resistance to fluids & tests: Specifies resistance to turbine oils and kerosene and references test conditions (see ISO 8668-2 for test methods); immersion time and fluid types are defined.

Applications and users

ISO 8668-3 is used by:

• Aerospace electrical and harness design engineers for standardized connector architectures
• Connector and terminal manufacturers specifying form-fit interchangeable modules
• Maintenance, repair & overhaul (MRO) teams and procurement specialists ensuring compliant replacement parts
• Certification and systems engineers verifying environmental and fluid resistance for aircraft electrical installations

Practical applications include designing terminal junction panels, wiring harness interfaces, and specifying modular feedthrough/feedback blocks for avionics, engine controls and airframe systems.

Related standards

• ISO 8668‑1 (Characteristics)
• ISO 8668‑2 (Tests - referenced for qualification procedures)
• MIL-I-81969 (tooling/connector handling - normative reference in the document)
• Relevant IEC electromechanical component vocabularies (referenced)

Keywords: ISO 8668-3:1994, terminal junction system, aircraft connectors, feedthrough module, feedback module, crimp contacts, sealing plugs, aerospace electrical standard.