EN 4158:2006

Overview

EN 4158:2006 specifies a test method for the measurement of electrical surface resistance of electrically conducting surface coatings used in aerospace applications. The standard applies to conductive paints and varnishes on non-conductive parts and to conductive layers that are overcoated by non-conductive layers when electrical contact areas are provided. The procedure verifies coating performance relevant to grounding, charge dissipation and electromagnetic interference (EMI) mitigation.

Key Topics

• Principle: Apply a known voltage to the conductive layer, measure the resulting current and calculate resistance using Ohm’s law. The standard provides the relationship to convert measured values to the layer resistance accounting for electrode geometry and test assumptions.
• Assumptions and limits: Homogeneous distribution of conductive particles, layer thickness < 1 mm, electrode contact geometry and sample size requirements to ensure valid results.
• Apparatus: A fixed-electrode assembly with conductive silicone elastomer electrodes mounted on an insulating support and standard electrical measuring instruments (ohmmeters/multimeters) with appropriate range and calibration.
• Key electrode data from the standard:
  • Electrode contact diameter (d): 4 mm
  • Typical center-to-center electrode spacing (a): 50 mm
  • Contact resistance: ≤ 0.2 Ω
  • Insulating resistance of support: ≥ 10^10 Ω
• Environmental and conditioning: Measurements are taken after complete curing of the conductive paint. Ambient temperature should be between 15 °C and 35 °C and relative humidity below 70%.

Applications

EN 4158:2006 is used by aerospace manufacturers, coatings suppliers, test laboratories and quality teams to:

• Confirm the electrical continuity and surface resistivity of conductive coatings on aircraft and spacecraft components.
• Support design and verification activities for earthing/grounding, static charge control and EMI/EMC considerations.
• Provide a repeatable, documented test procedure for contractual acceptance, supplier qualification and in-service inspections.

Practical test notes:

• Test specimens should normally be at least 300 mm × 300 mm. When coatings are overlaid with non-conductive paint, protected contact areas (10 mm diameter with 50 mm centre spacing) must be provided for measurement.
• The electrode assembly should be checked on a low-resistance metal surface before measuring to ensure correct zero and infinite readings on the instrument.

Related Standards

• ISO 1513 - sample preparation for paints and varnishes testing (referenced for specimen handling)
• ISO 3696 - water quality for analytical laboratory use

When citing or applying this method, include the standard reference EN 4158:2006 and report key test parameters (coating type, drying conditions, electrode geometry, instrument and measured values) as required by the standard's test report section.