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Aircraft electrical wires, cables, harnesses and connectors installed in designated fire zones may be required to continue performing defined safety functions while exposed to a representative powerplant fire.
Fire testing evaluates more than whether insulation burns. Depending on the applicable requirement, it can assess conductor continuity, insulation resistance, leakage current, connector functionality, firewall integrity, vibration tolerance and the ability of an installed assembly to support safe engine or auxiliary power unit shutdown.
ISO 2685:1992 contains a detailed normative method for single-core, multicore and screened cables. It also defines separate requirements for mated electrical connectors and connector assemblies installed through firewalls. Its electrical method combines a standard flame with vibration and live electrical monitoring.
The April 2023 draft prEN 3475-408 develops the cable method further. It references ISO 2685:1998 for the fire environment, introduces a defined liquid-fuel burner configuration, specifies a 500 mm square test frame, expands the fluid-conditioning programme and requires continuous monitoring of continuity and insulation performance.
The April 2023 document is explicitly a draft for enquiry. It contains unresolved work-in-progress text and provisional values. It must not be presented as an issued European Standard or used without agreeing how its unresolved provisions will be treated.
At installation level, SAE AS6826 makes an equally important point. Qualification to a wire, connector, TSO, AS/EIA or military component specification is not necessarily sufficient. The complete electrical wiring interconnection system, or EWIS, must be reconciled with its installed powerplant fire-intended function, firewall role, vibration environment and residual-flame requirements.
Aircraft wire, harness and connector fire testing is the controlled exposure of representative electrical hardware to a calibrated fire environment while defined electrical and mechanical conditions are applied.
The testing can assess:
Conductor continuity.
Core-to-core insulation.
Core-to-screen insulation.
Leakage current.
Connector contact continuity.
Connector insulation leakage.
Performance under simultaneous vibration.
Resistance to flame penetration through a firewall.
Backside ignition.
Residual flame behaviour.
Continued performance of a defined fire-intended function.
The May 2026 draft SAE ARP8998 uses the following distinctions:
| Term | Meaning |
|---|---|
| Wire | An insulated single metallic conductor without a metallic covering, sheath or shield. |
| Electrical cable | Two or more insulated conductors in a common covering, conductors twisted or moulded together, or an insulated conductor with a metallic shield or outer conductor. |
| Harness | An assembly of wires, electrical or optical cables and terminations designed so that it can be installed and removed as a unit. |
| Bundle | Wires, cables or harnesses routed and supported together for part of the installation. |
These distinctions matter.
Qualification of an individual wire does not automatically demonstrate the performance of a finished harness containing:
Connectors.
Contacts.
Terminations.
Branches.
Splices.
Backshells.
Overbraid.
Protective sleeving.
Supports.
Clamps.
Breakouts.
Firewall seals.
Installation interfaces.
The engineering objective is to determine whether the electrical item can:
Maintain the required electrical path during fire exposure.
Avoid unacceptable short circuits or leakage paths.
Perform the function required during an emergency action.
Avoid introducing an additional fire hazard.
Protect a firewall penetration where applicable.
Resist the combined effect of fire and vibration.
Produce evidence representative of the intended installation.
Support the agreed certification or qualification route.
Powerplant wire fire testing should not be confused with a short-duration wire-flammability or self-extinguishing test.
A self-extinguishing test generally evaluates:
Burn length.
Flame time after removal of the ignition source.
Flaming drips.
Propagation behaviour.
A powerplant fire-resistance test evaluates electrical or installation performance during a severe five-minute or 15-minute calibrated fire exposure.
The two activities answer different engineering questions.
Engineering teams identify:
Circuits routed through designated fire zones.
Circuits used during emergency procedures.
Fire-detection wiring.
Fuel shut-off wiring.
Engine-control wiring.
Firewall penetrations.
Shared harness interfaces.
Required fire-resistant or fireproof classifications.
Wire, cable, shielding, protective covering, terminals and connectors are selected using applicable component specifications.
Component qualification is useful evidence. It does not automatically substantiate the finished installation.
The production-representative configuration should include:
Actual wire constructions.
Representative terminations.
Connector bodies and inserts.
Backshells.
Protective materials.
Branches and breakouts.
Clamps and restraints.
Support spacing.
Firewall interfaces.
Features affecting heat flow or flame exposure.
Applicable testing may be conducted at one or more levels:
Wire or cable.
Connector.
Harness.
Bundle.
Firewall penetration.
Installed powerplant EWIS assembly.
The relationship between the test article and production installation must be documented.
Engine or APU qualification data must be reconciled with aircraft-level EWIS and powerplant fire-protection requirements.
The draft ARP8998 guidance emphasises coordination between:
The aircraft applicant.
The engine manufacturer.
The APU manufacturer.
Harness suppliers.
Equipment suppliers.
The certification authority.
Unclear ownership at the engine-to-aircraft interface is a common source of late compliance gaps.
A cable can retain its physical shape while losing electrical isolation.
Insulation may remain visually present while allowing unacceptable current leakage. A connector may remain attached while losing contact continuity. A harness can also fail at a termination or branch that was not represented during individual cable testing.
Visual survival alone is not proof of electrical survival.
EWIS components located in a designated fire zone and used during emergency procedures may need to remain functional during the fire.
Examples include:
Fire detection.
Fire warning.
Fuel shut-off.
Hydraulic shut-off.
Engine shutdown.
Propeller feathering.
Valve actuation.
Continued annunciation.
Controlled safe failure.
The required function and duration must be defined before testing.
A connector or harness penetration through a firewall can have two separate obligations:
Maintain the required electrical function.
Maintain the required fire-barrier function.
ISO 2685:1992 permits connector-function and firewall-integrity tests to be conducted simultaneously. It applies different acceptance criteria to each function.
A connector can therefore pass its electrical criterion but fail its firewall criterion, or vice versa.
Combining calibrated flame exposure, vibration and electrical monitoring produces evidence under interacting conditions.
This is stronger than assuming that separate flame, vibration and electrical tests automatically represent combined behaviour.
SAE AS6826 requires electrical wires and connectors within a designated fire zone to be considered at powerplant-system integration level.
It states that compliance with a component electrical standard is not necessarily sufficient to satisfy the installation requirements of AS6826.
Annex D of ISO 2685:1992 is a normative electrical-test annex covering:
Single-core cables.
Multicore cables.
Multicore screened cables.
Mated electrical connectors.
Connectors used in firewall applications.
The standard flame is defined as:
| Parameter | Requirement |
|---|---|
| Temperature | 1,100°C ±80°C |
| Absorbed heat-flux density | 116 kW/m² ±10 kW/m² |
| Fire-resistant duration | Five minutes |
| Fireproof duration | 15 minutes |
The 1992 edition requires the cable or connector specimen to be vibrated across its axis between 30 Hz and 60 Hz at a minimum acceleration of 4g
ISO 2685:1998 cancelled and replaced the 1992 edition.
The 1998 edition retained the common fire environment but changed the status of some product-specific annexes. Annexes C, D and E became informative rather than normative pending separate product standards.
This distinction matters. A customer specification, approved test procedure or certification plan may still invoke the product-specific conditions. Their contractual or certification status should be established before testing.
The April 2023 prEN 3475-408 draft normatively references ISO 2685:1998 for the fire environment, burner arrangements and calibration methods.
The April 2023 draft specifies a method for testing the fire resistance of fireproof electrical cables. It was intended to supersede EN 3475-408:2005.
Its identified significant technical change is the introduction of liquid-burner requirements and the associated test configuration.
The reviewed document explicitly states that it:
Is not yet a European Standard.
Was distributed for review and comment.
Was subject to change.
Must not be referred to as a completed European Standard.
The draft also contains unresolved text concerning peak-current and time acceptance. This issue must be addressed in the controlled test specification.
SAE AS6826 standardises powerplant fire-test methods, calibration, boundary conditions and pass/fail criteria.
For electrical wires and connectors, it particularly affects:
Test-article representativeness.
Fire-intended functions.
Induced vibration.
Standard-flame application.
Residual flames.
Firewall interfaces.
Boundary conditions.
Test planning and reporting.
Reconciliation between component qualification and installed compliance.
AS6826 identifies a non-resonant frequency between 30 Hz and 60 Hz at a minimum acceleration of 4g for electrical cables and connectors.
The 1 May 2026 draft ARP8998 is intended to provide a consistent approach to engine and APU EWIS fire-protection compliance and to supplement AS6826.
It states that where EWIS fire testing is required, the testing must comply with AS6826.
Because ARP8998 remains a draft, its content should be treated as developing recommended practice rather than an issued SAE requirement.
FAA AC 20-135 Change 1 removed the previously listed propane and oxy-acetylene options for powerplant component testing.
The FAA concluded that propane does not represent a combustible fluid likely to exist in an engine and that a propane burner may produce a less severe test than a kerosene burner using a representative combustible fluid.
This does not automatically invalidate historical approvals. It does affect the burner strategy for new or revised powerplant compliance programmes.
| Area | ISO 2685:1992 Annex D | prEN 3475-408:2023 draft |
|---|---|---|
| Document status | Issued standard, Annex D normative | Draft for enquiry |
| Specimen quantity | Three per cable construction | Six randomly selected specimens |
| Minimum specimen length | 0.75 m | 0.75 m |
| Conditioned length | Middle 0.5 m | Centre 0.5 m |
| Conditioning time | 24 hours | 24 hours |
| Post-conditioning stand | Not stated in the same form | One hour after surplus fluid removal |
| Fluid conditions | Three | Five listed fluids |
| Test frame | Dedicated prescribed arrangement | 500 mm × 500 mm square frame |
| Vibration frequency | 30 to 60 Hz | 30 Hz ±5 Hz |
| Vibration acceleration | 4g minimum | 4g minimum |
| Continuity current | Approximately 2 A | Approximately 2 A |
| Circuit check | 25 mA | 25 mA |
| Leakage limit | Expressed through 10,000 Ω insulation criterion | 12.5 mA maximum, corresponding to 10,000 Ω |
| Data recording | Functional monitoring required | Continuous recording required |
| Burner options | ISO 2685 burner arrangements | Liquid-fuel Method A or gas Method B |
| Residual behaviour | Not stated in the same draft wording | No re-ignition on the flame side after removal |
| Unresolved content | No | Peak-current/time criterion remains work in progress |
The ISO 2685:1992 electrical-cable method explicitly requires fluid conditioning.
Three separate specimens are conditioned in:
Aviation fuel.
Engine lubricating oil.
Hydraulic oil.
The April 2023 draft expands the listed fluids to:
Aircraft fuel or kerosene.
Phosphate-base hydraulic fluid.
Synthetic lubricant.
Isopropyl-alcohol cleaning product.
Ethylene-glycol de-icing fluid.
The programme must confirm which fluids are applicable. The draft wording should not be interpreted to mean that every fluid is automatically required for every cable construction without reviewing the governing specification.
Define whether the required classification is fire resistant or fireproof.
Identify the fire-intended function of each circuit.
Separate cable, harness, connector and firewall requirements.
Define the applicable standard and edition.
Identify whether a draft standard is being invoked.
Agree unresolved provisions with the customer or certification authority.
Define the required burner and fuel.
Establish continuity, leakage and insulation criteria.
Define vibration conditions.
Establish test-article conformity requirements.
Agree reporting and witnessing requirements.
Select representative specimens.
Record conductor size.
Record insulation construction.
Record shielding and jacket construction.
Record protective covering.
Complete the specified fluid conditioning.
Configure the required electrical-monitoring circuits.
Assemble mated connector specimens with required accessories.
Verify test-frame geometry.
Apply the specified initial tension.
Lock the specimen and remove temporary weights where required.
Verify vibration direction.
Verify burner orientation.
Complete pre-test electrical checks.
Complete the safety assessment.
Stabilise and calibrate the burner.
Verify flame temperature.
Verify heat flux or heat-transfer performance required by the governing method.
Confirm electrical-monitoring circuits.
Start vibration.
Start data acquisition.
Apply the calibrated flame.
Continuously monitor electrical performance.
Monitor flame behaviour.
Record any discontinuity or leakage event.
Maintain the required fire-intended function.
Remove the flame after the required duration.
Continue monitoring for the defined post-exposure period.
Complete any required post-test burner validation.
Identify loss of continuity.
Review leakage-current history.
Review insulation-resistance history.
Distinguish transient indications from sustained failures.
Apply the agreed transient acceptance rule.
Review connector contact performance.
Check for flame passage.
Check for backside ignition.
Review residual flames.
Confirm vibration compliance.
Confirm burner validity.
Determine whether the fire-intended function was maintained.
Record test-article identity.
Record the complete configuration.
Include conditioning evidence.
Include burner calibration evidence.
Include vibration evidence.
Provide time-correlated electrical data.
Record anomalies and deviations.
Include photographs and video references.
State results against each acceptance criterion.
State separately whether the cable, connector, harness and firewall functions passed.
Obtain deviation disposition where required.
Three specimens, each 0.75 m long, are used.
The middle 0.5 m of each specimen is immersed for 24 hours at ambient temperature. A separate specimen is used for:
Aviation fuel.
Engine lubricating oil.
Hydraulic oil.
Six specimens of at least 0.75 m are selected.
The centre 0.5 m is immersed for 24 hours at ambient temperature. After removal:
Surplus fluid is removed using a lint-free cloth.
The specimen stands for one hour.
The applicable cable-monitoring arrangement is installed.
The specimen is mounted on the test frame.
The ISO 2685:1992 method identifies the following initial cable weights:
| Cable size | Initial weight |
|---|---|
| AWG 22 to AWG 12 | 170 g |
| AWG 10 to AWG 4 | 340 g |
The April 2023 draft specifies a 500 mm × 500 mm square frame.
Its figures identify provisional weights of:
170 g for cable sizes 004 to 030.
340 g for cable sizes 050 to 220.
Both draft values are marked “to be reviewed”.
After tensioning, the specimen is locked at both ends and the weights are removed. This prevents excessive loading during vibration or resonance.
Frequency: 30 Hz to 60 Hz.
Minimum acceleration: 4g.
Direction: across the cable or connector axis.
Frequency: 30 Hz ±5 Hz.
Minimum acceleration: 4g.
Vibration perpendicular to the cable axis.
Vibration perpendicular to the burner axis.
No longitudinal vibration along the cable axis.
For electrical cables and connectors:
Use a non-resonant frequency between 30 Hz and 60 Hz.
Apply a minimum acceleration of 4g.
Measure the required level before flame application.
Maintain the calibrated input during the required exposure.
The test arrangement must not allow vibration to change the burner-to-specimen distance.
The April 2023 draft specifies:
Kerosene complying with the referenced fluid standard.
An ISO 2685:1998-style liquid burner or equivalent.
A 318 mm extension.
An outlet approximately 152 mm high and 280 mm wide.
A 152 mm cable exposure length.
Horizontal burner orientation.
Flame temperature of 1,100°C ±80°C.
Heat-flux density of 116 kW/m² ±10 kW/m².
A nominal calibration distance of 100 mm with the stated tolerance.
The draft specifies:
An ISO 2685:1998-style gas burner or equivalent.
A 152 mm cable exposure length.
Flame width or diameter at least twice the cable diameter.
Vertical burner orientation.
Flame temperature of 1,100°C ±80°C.
Heat-flux density of 116 kW/m² ±10 kW/m².
A nominal calibration distance of 75 mm with the stated tolerance.
The liquid-fuel method is relevant to current powerplant fire-test policy.
FAA AC 20-135 Change 1 removed propane and oxy-acetylene options for main powerplant component testing because kerosene produced more severe and representative heating in the FAA evaluation.
However, the April 2023 prEN draft still describes both liquid and gas methods. The selected method must therefore follow the governing specification, programme requirement and certification agreement.
Under ISO 2685:1992:
Continuity is indicated by approximately 2 A.
The insulation-degradation circuit is checked using a 25 mA indication.
Continuity must remain during the applicable exposure.
Insulation resistance must remain at least 10,000 Ω.
The 2023 draft uses a nickel-plated copper strand wrapped around the flame-exposed cable section to detect leakage.
It requires:
Approximately 2 A line current.
A 25 mA circuit check.
Continuous monitoring.
Leakage current not exceeding 12.5 mA.
Electrical checks before, during and after the test.
Multicore cables use a dedicated circuit to monitor:
Conductor continuity.
Core-to-core insulation degradation.
Leakage between conductors.
Time of any failure event.
The circuit arrangement must match the cable construction and agreed acceptance criteria.
For screened constructions:
Cable cores are connected together for the core-to-screen integrity test.
The grouped conductors are monitored against the metallic screen.
The circuit must detect unacceptable loss of electrical isolation during exposure.
Under ISO 2685:1992, the test article is a representative mated connector pair with required accessories.
The connector is:
Wired using fire-resistant cable.
Configured with all contacts connected in series.
Loaded at the nominal current specified for the connector.
Subjected to flame and vibration.
Electrical failure is defined by:
Any discontinuity during the five-minute flame application.
Leakage above the connector-specific limit during the subsequent one-minute check.
The connector-specific leakage limit must be defined before testing.
For a connector intended for a firewall application, ISO 2685:1992 requires, over 15 minutes:
No flame passage through the mounting plate.
No spontaneous ignition on the side away from the flame.
A firewall connector assembly must therefore be evaluated both as:
An electrical connection.
Part of the firewall barrier.
At installation level, the electrical circuit may need to demonstrate a specific action during the fire.
Examples include:
Fire detector annunciation.
Closure of a fuel shut-off valve.
Engine shutdown command.
Continued signal transmission.
Safe failure.
Maintenance of shutdown after the electrical control fails.
The pass/fail criteria must state the required behaviour and timing.
Visual Survival Mistaken for Electrical Survival
A cable can look intact after the test while electrical leakage has exceeded the permitted limit.
Control: Record continuity, leakage and insulation performance continuously.
Incomplete Harness Representation
Testing only a straight cable specimen can omit a vulnerable termination, connector, branch, splice, backshell or protective sleeve.
Control: Define which level of assembly is being qualified and justify representativeness.
Incorrect Vibration Direction
The 2023 draft rejects longitudinal vibration along the cable axis.
Control: Record the cable axis, burner axis and vibration axis in the test procedure.
Non-Representative Burner Selection
Gas and liquid-fuel flames can create different heating effects even where nominal temperature and heat-flux targets are similar.
Control: Agree the burner method before testing and document the certification basis.
Undefined Transient Criteria
The 2023 draft contains unresolved text concerning peak current and time.
Control: Define how transient leakage events will be assessed before the test begins.
Potential causes include:
Twenty-four-hour fluid conditioning.
One-hour post-conditioning stand time.
Multiple fluid conditions.
Multiple cable constructions.
Separate harness features.
Connector and firewall tests.
Burner calibration failure.
Unstable electrical monitoring.
Incomplete vibration evidence.
Certification-authority witness availability.
Testing costs increase when the scope does not distinguish between:
Material flammability.
Wire self-extinguishing performance.
Cable fire resistance.
Connector functionality.
Harness-level functionality.
Firewall-penetration integrity.
Installed EWIS compliance.
The correct evidence level should be agreed before committing hardware.
Using a component certificate without reconciling:
Burner type.
Flame severity.
Exposure duration.
Vibration.
Electrical loading.
Fluid conditioning.
Harness construction.
Firewall role.
Installed function.
can leave a compliance gap.
Common weaknesses include:
No standard edition stated.
Missing fluid identity.
Missing conditioning duration.
No record of the stand period.
Undefined electrical acceptance limits.
No time-correlated electrical data.
Incomplete vibration evidence.
No connector-loading rationale.
Firewall and electrical results combined into one unclear conclusion.
Use of a draft standard without recording agreed interpretations.
Missing configuration-control evidence.
State exactly what each circuit must do during the fire.
Examples include:
Detect the fire.
Maintain an alarm.
Transmit a shutdown command.
Actuate a valve.
Support safe engine shutdown.
Remain electrically isolated.
Fail safely without creating an additional hazard.
Maintain separate evidence for:
Wire or cable qualification.
Connector qualification.
Harness or bundle performance.
Installed powerplant or firewall compliance.
Do not use one evidence level as an automatic substitute for another.
Include the cable construction and interfaces most likely to govern performance.
Critical features can include:
Small conductor size.
Thin insulation.
Multicore construction.
Metallic screen.
Outer jacket.
Tight bend.
Splice.
Branch.
Connector backshell.
Firewall seal.
Clamp location.
Mechanical restraint.
Highest electrical load.
Critical fire direction.
Define:
Continuity current.
Permitted interruption, if any.
Leakage-current limit.
Minimum insulation resistance.
Sample rate.
Connector-specific leakage criterion.
Treatment of transient peaks.
Required post-test checks.
Identify:
Wire specification.
Wire gauge.
Insulation system.
Number of cores.
Screen or overbraid.
Jacket.
Protective sleeve.
Terminals.
Contacts.
Connector.
Backshell.
Splices.
Breakouts.
Mounting.
Restraint.
Firewall seal.
Penetration arrangement.
Continuous data provides the time of:
Continuity loss.
Leakage increase.
Insulation breakdown.
Recovery.
Intermittent failure.
Connector malfunction.
It is more defensible than pre-test and post-test measurements alone.
The procedure should define:
Burner orientation.
Burner-to-specimen distance.
Flame coverage.
Cable axis.
Vibration axis.
Frame geometry.
Specimen restraint.
Instrumentation position.
Movement tolerances.
When using prEN 3475-408:2023:
Identify it as a draft.
Record the exact draft date.
List unresolved provisions.
Define agreed interpretations.
Obtain customer or authority acceptance.
Avoid claiming compliance with a final European Standard.
Early coordination should cover:
Applicable regulations.
Means of compliance.
Fire classification.
Burner method.
Boundary conditions.
Specimen representativeness.
Electrical criteria.
Firewall criteria.
Residual flames.
Draft-standard interpretations.
Report content.
Certification Plan.
EWIS Fire-Protection Compliance Matrix.
Fire-Safety Assessment.
Fire-Intended-Function Assessment.
Engine-to-Aircraft Interface Document.
Means-of-Compliance Statement.
Similarity Assessment.
Comparative Analysis Report.
Component-to-Installation Reconciliation.
Qualification Test Plan.
Test-Article Configuration Definition.
Fluid-Conditioning Record.
Electrical Circuit Schematic.
Connector Contact-Loading Schedule.
Burner Calibration Report.
Heat-Flux or Heat-Transfer Calibration Record.
Vibration Survey.
Vibration Control Record.
Test Procedure.
Test Readiness Review Record.
Deviation Record.
Photographic and Video Record.
Qualification Test Report.
Drawings.
Bills of Material.
Wire and Cable Specifications.
Connector Specifications.
Backshell Specifications.
Harness Manufacturing Instructions.
Conformity Records.
Material Certificates.
Change-Control Records.
Installation Drawings.
Firewall-Penetration Details.
The required electrical path remains intact throughout the applicable five-minute or 15-minute exposure.
The cable remains within the applicable insulation-resistance and leakage-current limits.
Under the reviewed 2023 draft, the maximum current value is 12.5 mA, corresponding to an insulation resistance of 10,000 Ω within the specified circuit.
No prohibited discontinuity occurs during the required functional period.
Post-exposure leakage remains within the connector-specific limit.
The required emergency or safety function is completed and maintained for the specified duration.
No flame passes through the connector mounting plate.
No ignition occurs on the non-flame side during the applicable 15-minute test.
Post-flame behaviour satisfies the applicable method and integration-level acceptance criteria.
The April 2023 draft requires no re-ignition on the flame side after flame removal.
SAE AS6826 applies wider residual-flame requirements at powerplant-system integration level.
The burner, vibration, electrical monitoring and boundary conditions remain within the agreed limits.
Component-level evidence is successfully reconciled with the complete EWIS installation and its AS6826 fire-intended-function, firewall and residual-flame requirements.
Resonate Testing can support teams to:
Review the applicable standard and edition.
Separate wire, harness, connector and firewall requirements.
Define fire-resistant and fireproof classifications.
Identify the relevant evidence level.
Develop a controlled compliance and test strategy.
Engineering support can include:
Interpretation of ISO 2685 requirements.
Review of prEN 3475-408 draft provisions.
Identification of unresolved draft content.
Definition of electrical monitoring.
Review of flame and vibration geometry.
Reconciliation of component qualification with AS6826 installation requirements.
Support may include:
Cable-conditioning campaigns.
Single-core cable testing.
Multicore cable testing.
Screened-cable testing.
Combined flame and vibration arrangements.
Electrical circuit development.
Liquid-fuel burner arrangements.
Gas-burner arrangements where applicable to the agreed method.
Connector-functional testing.
Firewall-penetration testing.
Harness-level testing.
Internal Resonate Testing development work records activity concerning wire fire-resistance and fireproof testing, vertical and horizontal burner arrangements, electrical monitoring, fluid preparation and rig tensioning.
The final scope remains subject to technical review, equipment suitability, safety assessment, resource availability and confirmation of accredited scope where an accreditation claim is required.
Support can include:
Continuity monitoring.
Leakage-current measurement.
Insulation-resistance monitoring.
Core-to-core monitoring.
Core-to-screen monitoring.
Time-correlated data acquisition.
Safe remote monitoring during flame exposure.
Resonate Testing can support preparation of:
Test plans.
Configuration definitions.
Representativeness statements.
Conditioning records.
Conformity records.
Test procedures.
Electrical schematics.
Deviation reports.
Test reports.
Electrical and fire-performance evidence packages.
Independent review can help:
Assess legacy ISO 2685 evidence.
Evaluate gas-versus-liquid-burner differences.
Review connector qualification applicability.
Assess harness-level coverage.
Challenge electrical acceptance criteria.
Identify component-to-installation compliance gaps.
Your Test Facilitator. Not simply a test facility.
What is the difference between wire, cable, bundle and harness testing?
Wire testing evaluates an individual insulated conductor. Cable testing can address multicore or screened constructions. A bundle contains wires, cables or harnesses routed together. A harness is an installable assembly that can include wires, cables, terminations and protective features.
Qualification at one level does not automatically substantiate every higher assembly level.
What flame is used for ISO 2685 cable testing?
ISO 2685 defines a standard flame temperature of 1,100°C ±80°C and an absorbed heat-flux density of 116 kW/m² ±10 kW/m².
What is the difference between fire-resistant and fireproof cable testing?
Fire-resistant testing uses a five-minute flame exposure. Fireproof testing uses a 15-minute flame exposure. The required electrical and installation functions must also be satisfied.
Is vibration applied during the fire test?
Yes, where the cited electrical cable and connector methods apply.
ISO 2685:1992 specifies 30 Hz to 60 Hz at a minimum of 4g across the component axis. The April 2023 draft specifies 30 Hz ±5 Hz at a minimum of 4g, perpendicular to the cable and burner axes.
Are cables conditioned in aircraft fluids before testing?
Yes, under the cited cable methods.
ISO 2685:1992 uses aviation fuel, engine lubricating oil and hydraulic oil. The April 2023 draft lists fuel, phosphate-base hydraulic fluid, synthetic lubricant, cleaning product and de-icing fluid.
How many cable specimens are required?
ISO 2685:1992 specifies three randomly selected 0.75 m cable specimens.
The April 2023 draft specifies six randomly selected specimens, each at least 0.75 m long.
How is cable continuity monitored?
The cited methods use approximately 2 A as the indication of continuity through the specimen.
What insulation resistance is required?
ISO 2685:1992 specifies a minimum of 10,000 Ω during the applicable exposure.
The reviewed 2023 draft also relates its 12.5 mA maximum-current criterion to 10,000 Ω within the specified circuit.
Does prEN 3475-408:2023 require continuous data recording?
Yes. The draft requires continuous recording of leakage current and insulation resistance throughout the test.
Is prEN 3475-408:2023 a final European Standard?
No. The reviewed April 2023 document explicitly states that it is a draft, is subject to change and must not be referred to as a European Standard.
Does the 2023 draft permit a kerosene burner?
Yes. Method A defines a liquid-combustible kerosene burner and a horizontal test arrangement.
Does the draft also permit a gas burner?
Yes. Method B defines a gas-burner arrangement. Its use must be reconciled with the governing programme and current powerplant fire-test policy.
How are multicore cables evaluated?
Multicore cables use a dedicated monitoring circuit to assess continuity and electrical isolation between conductors during simultaneous flame and vibration exposure.
How are screened cables evaluated?
The cable cores are connected together and monitored against the metallic screen to assess core-to-screen integrity.
How are electrical connectors tested under ISO 2685:1992?
A representative mated pair is fitted with required accessories, wired with fire-resistant cable, connected with contacts in series and loaded at its nominal current.
It is monitored for discontinuity during the five-minute flame exposure and for excessive leakage during a further one-minute period.
What additional requirement applies to firewall connectors?
No flame may pass through the mounting plate and no spontaneous ignition may occur on the side away from the flame during the 15-minute test.
Does a fire-rated connector automatically make the harness compliant?
No. SAE AS6826 states that compliance with a TSO, AS/EIA or military electrical standard is not necessarily sufficient for the installed powerplant application.
Installation-level fire function, firewall and residual-flame requirements must also be addressed.
Is a wire flammability test the same as a powerplant fire-resistance test?
No.
A wire flammability test normally assesses self-extinguishing behaviour after a short flame exposure. A powerplant fire-resistance test evaluates function or integrity during a severe five-minute or 15-minute calibrated fire.
Can legacy ISO 2685:1992 data still be used?
Potentially. The programme must confirm configuration similarity, standard edition, burner method, conditioning, vibration, electrical criteria and installation applicability.
Can a cable pass while the harness fails?
Yes.
Harness terminations, connectors, splices, branches, backshells, protective materials and restraints can introduce failure modes not represented by a straight cable specimen.
What are the most common causes of an invalid or challenged test?
Common concerns include:
Unrepresentative specimens.
Incomplete conditioning.
Incorrect burner configuration.
Inadequate calibration.
Wrong vibration direction.
Undefined electrical limits.
Missing continuous data.
Failure to assess transient leakage.
Incomplete connector loading.
Failure to reconcile component evidence with the installed harness or firewall function.
Powerplant EWIS Fire-Protection Compliance.
Wire, Cable, Bundle and Harness Terminology.
Self-Extinguishing versus Fire-Resistant Wiring.
Fire-Intended Functions for Engine Wiring.
Aircraft Harness Qualification Planning.
ISO 2685:1992 versus ISO 2685:1998.
prEN 3475-408 Cable Fire Testing Explained.
AS6826 Powerplant Fire-Test Standard.
AC 20-135 Change 1 and Kerosene Burners.
Fireproof versus Fire-Resistant Testing.
Aircraft Firewall Connector Testing.
Connector Continuity and Leakage Testing.
Wire-Bundle Firewall Seal Testing.
Flame Penetration and Backside Ignition.
Firewall Sealant Qualification.
Simultaneous Fire and Vibration Testing.
Cable Fluid Conditioning Before Fire Testing.
Continuous Electrical Monitoring During Fire Exposure.
Burner Temperature and Heat-Flux Calibration.
Writing an Aircraft Fire Qualification Test Report.
Resonate Testing supports the development and execution of aircraft electrical fire-test programmes covering cable conditioning, combined flame and vibration exposure, electrical continuity and insulation monitoring, connector functionality, firewall penetrations and AS6826 installation-level compliance.
Share the applicable standard, wire or cable specification, harness configuration, electrical loading, fire-intended function, installation details and acceptance criteria for technical review.
Whether you’re looking to contact us for the first time or have another testing requirement, we’d love to hear from you.
