SIST EN 3475-605:2018

Overview

SIST EN 3475-605:2018 is a European Standard developed by CEN, focusing on test methods for aerospace electrical cables used in aircraft. Specifically, this standard describes the Wet Short Circuit Test to evaluate the behavior of cable insulation under conditions where an electrical arc is initiated and sustained by contaminating fluids, typically aqueous solutions. This test method is essential for assessing the durability and safety of electrical cables in environments where moisture or fluid contamination might cause arcing, potentially leading to insulation failure or propagation of faults.

This standard complements EN 3475-100 and is primarily designed for electrical networks operating at 115 Vac, with additional provisions for 230 Vac networks. It covers specific procedures, apparatus, specimen configurations, and acceptance criteria to reliably simulate service conditions.

Key Topics

• Test Objective: The primary goal is to simulate and control failure phenomena seen in cable bundles damaged and contaminated by fluids, assessing the insulation’s tendency to track and allow electrical arc propagation back to the source.
• Cable Bundle Preparation: The test requires arranging seven cables in a hexagonal bundle (six around one), with precise spacing and use of glass lacing tape to maintain contact and positioning.
• Electrical Setup: The test circuit includes adjustable prospective fault currents, three-phase power supplies (115/200 V or 230/400 V at 400 Hz), protective circuit breakers rated per cable size, and critical components such as non-inductive ballast resistors to prevent overvoltage during arc extinction.
• Electrolyte Application: A defined electrolyte solution (3% sodium chloride in distilled water) is dripped onto the cable bundle at a controlled rate to simulate aqueous contamination and initiate arcing.
• Test Procedure: Conduct continuous testing with current and fluid flow for 2 hours or until circuit breakers trip, followed by power reapplication without fluid flow to observe fault development. Multiple testing cycles per cable size and current level ensure repeatability and qualification.
• Damage Assessment: Visual examination includes measuring char length, noting arc tracking effects, and recording any insulation or thermal damage. Detailed documentation is required in test reports, including cable identification, power source characteristics, circuit breaker operations, and damage observations.
• Scope of Cable Sizes and Fault Currents: Testing typically covers cable sizes 002, 006, and 020, with six defined levels of prospective fault currents appropriate to cable cross-sections to address realistic fault scenarios.

Applications

SIST EN 3475-605:2018 provides invaluable guidance for aerospace manufacturers and testing laboratories to:

• Verify the insulation integrity and safety of aircraft electrical cables exposed to moisture or fluid contamination.
• Ensure cable design meets stringent aircraft electrical system safety requirements and resistance to short-circuit and arc tracking failures.
• Support product qualification, acceptance testing, and certification in compliance with aerospace industry standards.
• Optimize design and selection of cables for the durability of electrical interconnections in critical aircraft environments where fluid exposure may occur.
• Facilitate compliance with regulatory and durability mandates across the European aviation sector and beyond.

Related Standards

• EN 3475-100: General testing requirements and methods for aerospace electrical cables, to be used conjointly with SIST EN 3475-605:2018.
• EN 2350: Technical specifications for aerospace circuit breakers, providing required trip characteristics for protective devices used in fault current tests.
• EN 3197: Design and installation guidelines for aircraft electrical and optical interconnection systems, useful for interpreting damage modes such as arc tracking versus short circuit effects.
• A-A-52083: Specification for glass lacing tape, referenced for cable bundling and securement during testing.

Keywords: SIST EN 3475-605:2018, aerospace cable testing, wet short circuit test, electrical arc insulation, aircraft cable insulation, cable arc tracking, electrical cable qualification, aircraft electrical safety standards, aerospace cable test methods, circuit breaker ratings, cable insulation failure, fluid contamination electrical testing.