Module 7.7 Electrical wiring interconnection system (EWIS)
943 words · checked 2026-10-03 · Pro
Knowledge level
| Sub-module | A | B1 / B3 | B2 / B2L |
|---|---|---|---|
| 7.7 EWIS | 1 | 3 | 3 |
B1, B2, B2L and B3 need level 3: detailed, practical knowledge. EWIS is also a favourite essay subject.
What is EWIS?
The EWIS is every wire, cable, connector, terminal, splice, clamp, conduit, grounding and bonding point, circuit-protection device and their supports installed in the aircraft to carry electrical energy or signals. Ageing and contaminated wiring has contributed to serious accidents (fires, fuel tank ignition), so EWIS inspection and cleanliness are emphasised in maintenance programmes ("protect and clean as you go").
Continuity, insulation and bonding testing
| Test | Instrument | Purpose |
|---|---|---|
| Continuity | multimeter/continuity tester (low voltage) | confirms an unbroken conductor path; circuit de-energised; isolate both ends |
| Insulation resistance | insulation tester (e.g. 250-500 V DC, as specified) | checks insulation between conductors and to ground; disconnect equipment and ESD-sensitive units first; typical minimum values in the megohm range per AMM |
| Bonding | low-resistance (milliohm) bonding tester, four-wire (Kelvin) method | confirms low resistance of bonding straps and component bonds (typically a few milliohms per joint, per manual) |
Key fact: Insulation testing uses high voltage - disconnect avionics and warn others before testing; never test fuel-tank wiring with standard insulation testers unless the procedure allows it.
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