EWIS — Electrical Wiring Interconnection System
Continuity, insulation and bonding testing; crimping and crimp inspection; connectors, looming, clamping, routing, and the separation and segregation of cables.
EWIS — summary notes
Free- EWIS covers the wires, connectors, terminations, looms, clamps and bonding that carry power and signals around the aircraft, and the practices that keep them serviceable.
- A crimped termination joins conductor to terminal by controlled deformation. Select the terminal for the wire gauge and stud size, strip without nicking strands, insert fully so bare wire shows in the inspection window, and crimp with a calibrated tool and the matching die. The ratchet prevents release until the crimp is complete.
- Crimp inspection: correct terminal and tool, crimp central and fully formed, insulation gripped where required, no cut or protruding strands, and a pull test where specified.
- Bonding connects metallic parts to a common low-resistance reference. It dissipates static, gives lightning and fault currents a safe path, prevents arcing and provides a stable earth reference. Bonds are measured in milliohms, and mating faces are cleaned to bare metal then re-protected against corrosion.
- Continuity testing proves a circuit is complete; insulation testing proves conductors are not leaking to each other or to earth. Insulation testers must not be applied to solid-state equipment.
- Routing and protection: respect minimum bend radii, clamp at the specified intervals, avoid chafing against structure, keep clear of hot areas and moving parts, and provide a drip loop so fluid runs off rather than into a connector.
- Separation and segregation keep power cables away from sensitive signal and screened cables so interference is not induced, and keep redundant system channels physically apart so one event cannot take out both.
- ⚠ Exam trap: bonding is tested for LOW RESISTANCE in milliohms — not for tensile strength or continuity alone.
- Bonding resistance
- measured in milliohms — check the AMM figure
- Crimp check
- correct die · full barrel · insulation gripped · no cut strands · pull test
- Separation
- power away from signal · redundant channels physically apart
A crimped terminal passes a visual check but pulls off the wire under a light load. What was most likely wrong?
The wrong die or terminal for the wire gauge, so the barrel was never fully compressed onto the conductor. A crimp that looks acceptable but has not been formed with the matching calibrated tool will not develop its designed mechanical grip.
Why are the two channels of a redundant system routed on opposite sides of the fuselage?
So that a single local event — a fire, a burst duct, structural damage or chafing at one clamp — cannot damage both channels at once. Physical separation is what makes the redundancy real rather than nominal.
EWIS concept map
FreeEWIS
EWIS quiz
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