EN 3661-005:2006

Overview

EN 3661-005:2006 is a European standard developed by CEN that defines the product requirements for single-pole, temperature compensated circuit breakers used in aerospace applications. These circuit breakers have a rated current range of 20 A to 50 A and are designed to operate reliably in demanding aircraft environments. Specifically, they function in temperatures from −55 °C to 125 °C and at altitudes up to 15,000 meters. The standard mandates the use of push-pull type actuators with delayed action "trip-free" tripping mechanisms and includes polarized signal contacts for enhanced electrical monitoring and safety.

This standard ensures consistent specifications for circuit breakers in aircraft onboard electrical circuits, addressing electrical performance, mechanical durability, environmental resistance, and dimensional uniformity. It also specifies marking, designation, and delivery codes to facilitate identification, installation, and compliance verification.

Key Topics

• Temperature Compensation: Circuit breakers maintain accurate tripping behavior across a wide temperature range (−55 °C to 125 °C), ensuring dependable protection under extreme aerospace conditions.

• Rated Current Range: Covers circuit breakers rated from 20 A to 50 A that meet stringent aerospace safety and performance requirements.

• Polarized Signal Contact: A key feature is a signal contact that is electrically polarized - open when main contacts are closed and vice versa. This provides reliable status signaling critical for aircraft electrical system monitoring.

• Push-Pull Actuator with Trip-Free Tripping: The breaker mechanism features a single push button actuator with delayed action trip-free characteristics, preventing mechanical lock during faults.

• Environmental and Mechanical Durability:

  • Resistant to vibrations (up to 10 gn sinusoidal, 5.8 gn random, 3 gn at altitude)
  • Resistance to shocks up to 50 gn
  • Endurance tested for at least 2,500 load operations and 5,000 no-load operations
  • Corrosion, humidity, contaminant, and lightning over-voltage resilience as per aerospace standards

• Electrical Performance:

  • Rated for nominal voltages of 28 V DC and up to 115 V AC (360 Hz to 800 Hz)
  • Maintains function up to specified short circuit currents (up to 4,000 A DC and 2,000 A AC prospective currents)
  • Defined voltage drop and trip threshold limits at varying temperatures and altitudes

• Standard Compliance and Reference:

  • Integrates related aerospace standards like EN 3661-001 (technical specification), EN 3661-3841-305 (test methods), and EN 6113 (hardware)
  • Harmonizes with military and national standards for installation tools and components

• Marking and Identification:

  • Clear labeling includes standard designation, rated current code, manufacturer info, manufacturing date, wiring diagram, and part number.
  • Color coding of actuators (such as green buttons) and terminal identifications ensure correct installation.

Applications

The EN 3661-005:2006 standard is essential for manufacturers, maintenance providers, and aerospace engineers working with aircraft electrical systems. It ensures the selection and use of circuit breakers that:

• Protect aircraft onboard circuits from overloads and short circuits
• Operate reliably under significant temperature extremes and high altitudes
• Provide safe electrical disconnection with beneficial signal feedback via polarized contacts
• Fit standardized mounting panels and use compatible hardware kits to simplify integration into aeronautical equipment

Typical applications include power distribution panels, avionics protection, propulsion control systems, and other critical electrical subsystems where compliance with recognized quality and safety standards is mandatory. These circuit breakers contribute to flight safety by safeguarding electrical components and helping maintain system integrity during faults.

Related Standards

• EN 3661-001: Technical specifications for temperature compensated circuit breakers in aerospace.
• EN 3841-305: Test methods for assessing short circuit performance of circuit breakers.
• EN 6113: Connecting and attachment hardware standards essential for installation conformity.
• TR 6083: Panel cut-out specifications for secure mounting of electrical components.
• MIL Standards: Military specifications for electrical contact tools (MIL-I-81969 series) and semiconductor devices (MIL-S-19500 diodes) employed in circuit breaker auxiliary contacts.
• FED-STD-595B: Standard for colors used in government procurement, ensuring consistent actuator identification.

Keywords: EN 3661-005:2006, aerospace circuit breakers, single-pole circuit breakers, temperature compensated circuit breakers, polarized signal contact, aircraft electrical systems, aviation circuit protection, aerospace electrical components, push-pull actuator, trip-free circuit breaker, circuit breaker standard, aviation safety equipment, high-altitude electrical protection.