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
- 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
EWIS
EWIS quiz
EWIS, quiz
1. Bonding in EWIS is primarily tested for:
Electrical continuity and low resistanceTensile strengthColour coding2. Bonding resistance is measured in:
MilliohmsMegohmsKilohms3. The purposes of bonding include:
Static dissipation and a safe path for lightning and fault currentIncreasing the structural strength of the joint by tying the two members together electricallyReducing cable weight, since a bonded structure can serve as the return path for every circuit4. When making a crimped connection the conductor must be:
Fully inserted, with bare wire visible in the inspection windowInserted half wayLeft slightly short of the barrel5. Insulation must be stripped:
Without nicking or severing strandsBy burning it offWith side cutters6. The ratchet on a crimp tool:
Prevents release until a full crimp is formedSpeeds the operationMeasures the wire gauge7. A crimp inspection includes checking that:
No strands are cut or protruding and the crimp is centralThe wire is warmThe terminal is painted8. Bonding surfaces are prepared by:
Cleaning to bare metal, then re-protecting after connectionPainting before assemblyApplying grease9. Power cables are separated from sensitive signal cables to:
Prevent induced interferenceSave weightSimplify the loom10. Redundant system channels are routed apart so that:
A single local event cannot damage bothThe looms are easier to buildVoltage drop is reduced11. A drip loop in a cable run is provided so that:
Fluid runs off rather than into the connectorThe cable can stretchThe loom looks tidy12. Continuity testing proves:
The circuit path is completeThe insulation is soundThe bonding is adequate