FAA 25.1707 — System Separation Requirements

The Federal Aviation Regulation that requires EWIS to be physically separated and electrically isolated from other EWIS, aircraft systems, fluid lines, control cables, and heated equipment such that no credible failure can produce a hazardous condition.

Technical detail

14 CFR §25.1707 contains subparts (a) through (j). Subpart (a) sets the overarching separation standard. Subparts (b)–(d) cover electrical interference, heavy current cable separation, and grounding/power source independence. Subparts (e)–(h) address separation from fuel, hydraulic, oxygen, water, and waste systems. Subpart (i) covers flight and mechanical control cables. Subpart (j) covers heated equipment and hot-air ducts.

The regulation does not adopt fixed separation distances. Compliance is demonstrated by damage assessment — physical testing, simulation, or a combination — substantiating that a credible EWIS failure cannot create a hazardous condition. Industry guidance such as AS50881 provides starting points, but the regulation supersedes industry recommendations.

When it matters

Any modification that re-routes wiring, changes harness composition, or adds high-current loads requires a §25.1707 compliance argument. Inspectors expect a damage assessment with measured data — not a citation to AS50881's default 0.500″ separation.

Related terms

Electrical Wiring Interconnection System
Every wire, wiring device, and combination thereof installed in any area of an aircraft for transmission of electrical energy between two or more termination points, including supporting components such as clamps, connectors, and bundle hardware.
FAA 25.1701 — EWIS Definition and Scope
The Federal Aviation Regulation that defines what an Electrical Wiring Interconnection System is and identifies the components in scope of the §25.1700 series.
SAE AS50881 — Wiring Aerospace Vehicle
The SAE aerospace standard that establishes recommended practice for the design, installation, and verification of aerospace wiring systems. Widely referenced as supporting guidance for FAA §25.1707 compliance.
Arc Damage Modeling Tool
Lectromec's arc damage simulation tool. Simulates wire failures that produce arcing events and the subsequent damage to nearby harnesses, structure, and fuel or hydraulic lines. Used in certification packages for aerospace organizations.
Wet Arc Track Propagation
A failure mode in which a contaminating fluid lowers the surface dielectric strength of wire insulation, allowing an arc to track along the insulation and propagate from a single initial breach to multiple adjacent conductors.