Overview - ISO 2678:1985 (Insulation resistance & high voltage tests)
ISO 2678:1985 specifies environmental electrical tests for aircraft equipment focused on insulation resistance and high voltage (dielectric) tests. It is part of a broader series of standards for airborne equipment testing (see ISO 7137). The standard treats insulation-resistance and high-voltage testing as two distinct checks: a high insulation resistance alone does not guarantee absence of defects (cracks, flashovers); the high-voltage test proves dielectric withstand capability under an applied field. ISO 2678 applies to equipment intended for aircraft but does not cover insulation testing of equipment already installed in an aircraft.
Key topics and technical requirements
- Two separate tests: insulation resistance measurement and high-voltage (dielectric) test; both are required to assess insulation integrity.
- High-voltage test:
- Performed with sinusoidal AC voltage (r.m.s. values given in the standard).
- Voltage ramped from zero to test value, held for the specified duration, then ramped down (voltage change rate limited to 500 V/s).
- High-voltage testing is not permitted on semiconductor-containing items that cannot be disconnected or bridged.
- Example AC test voltage levels in the standard include 500 V, 1 000 V and 1 500 V with specified dwell times (e.g., 1 min or 5–10 s depending on rated voltage).
- Insulation resistance test:
- Measured using a pure DC source; the standard specifies 500 ± 25 V DC measuring voltage.
- Measurements must be taken after readings stabilize and include live-to-live and live-to-case (earth) checks.
- Leakage current:
- Requirement for leakage current is explicit: leakage current shall not exceed 3 μA.
- A 0.5 MΩ resistor is specified in series for certain leakage current measurements.
- Insulation resistance minimums:
- Minimum resistance values are defined for four equipment categories (A–D) and differ when climatic tests are applied. For individual assemblies, minimums are increased as noted in the standard.
- Test reporting: mandatory elements include equipment ID, diagrams, methods, voltages, calibration status, ambient conditions, measured values, observations, test date and responsible signature.
Practical applications and users
- Who uses ISO 2678: aircraft equipment manufacturers, avionics designers, environmental test laboratories, maintenance and repair organizations, and certification authorities.
- Practical uses:
- Pre-delivery and post-repair verification of insulation and dielectric strength.
- Quality control during manufacturing and component selection for avionics.
- Supporting compliance evidence for safety and airworthiness assessments.
- Guiding test procedures in conjunction with environmental test programs (ISO 7137 / DO-160).
Related standards
- ISO 7137 - Aircraft: environmental conditions and test procedures for airborne equipment.
- EUROCAE ED-14A / RTCA DO-160A - referenced/endorsed material for environmental testing of avionics.
Keywords: ISO 2678:1985, insulation resistance, high voltage tests, aircraft equipment, electrical equipment, environmental tests, leakage current, dielectric test, avionics testing.
Open preview (PDF)Environmental tests for aircraft equipment — Insulation resistance and high voltage tests for electrical equipment
