EN 3475-802:2009

Overview

EN 3475-802:2009 - "Aerospace series - Cables, electrical, aircraft use - Test methods - Part 802: Capacitance unbalance" specifies a standardized method for measuring capacitance unbalance in digital data transmission cables used in aircraft. The standard covers measurement principles for both screened pairs and screened quads and is intended to be used together with EN 3475-100 (general test requirements) and EN 3475-801 (capacitance per unit length).

Key topics and requirements

• Scope: Measurement of capacitance unbalance within a pair or within quads (pair-to-pair and pair-to-ground) for aircraft data cables.
• Specimen preparation: Samples must be stripped and prepared for connection to the measuring device as indicated by the standard.
• Apparatus: Measurements are made using an unbalance bridge at a test frequency of (1 000 ± 100) Hz. Automatic or semi-automatic equipment may be used.
• Measurement methods:
  • Screened pair: Capacitance measured as per EN 3475-801; sample length of 3 m or more. The standard defines calculation of capacitance unbalance as a percentage.
  • Screened quad (pair-to-pair): Illustrates conductor numbering (1,2 for pair A; 3,4 for pair B). Sample length must be 100 m or more. Unbalance per unit length is calculated from conductor-to-conductor capacitances using the specified relationship Cpp = C13 + C24 − C23 − C14. The standard provides a normalization method to express results corrected to 100 m when different sample lengths are used.
  • Screened quad (pair-to-ground): Pair-to-ground unbalance uses measured conductor-to-screen capacitances (e.g., Cpg = C1o − C2o); minimum sample length 100 m. Normalization to 100 m is specified for other lengths.
• Requirement: Measured unbalance values shall not exceed the limits specified in the applicable product standard.

Applications and users

• Ensures signal integrity and limits common-mode conversion for digital aircraft data links (e.g., ARINC, MIL‑STD data pairs).
• Used by:
  • Aerospace cable manufacturers for design verification and production quality control
  • Avionics and aircraft OEM test laboratories for acceptance and qualification testing
  • Procurement and certification teams to verify compliance with product standards
  • EMC and signal-integrity engineers assessing cable suitability for digital transmission

Related standards

• EN 3475-100 - General test methods for aerospace electrical cables (mandatory companion)
• EN 3475-801 - Capacitance per unit length (referenced for measurement details)

Keywords: EN 3475-802:2009, capacitance unbalance, aerospace cables, aircraft data transmission cable, test methods, screened pair, screened quad, EN 3475-100, EN 3475-801, unbalance bridge.