Wire Splicing Improperly crimped splices can cause increased resistance, leading to overheating. Splicing should be kept to a minimum and avoided in high-vibration areas. Splicing of power wires, co-axial cables, multiplex bus, and large gauge wire should be avoided. Self-insulated splice connectors and environmentally-sealed AS7928 conformant splices are preferred. Splices should be located to permit inspection, and splices in bundles should be staggered so as to minimize any increase in the size of the bundle. Grounding and Bonding One of the more important factors in the design and maintenance of aircraft electrical systems is proper bonding and grounding—the process of electrically connecting conductive objects to a conductive structure or return path to complete a circuit. Inadequate bonding or grounding can lead to unreliable operation of systems, damage to sensitive electronics, shock hazard, or lightning strike damage. The design of the ground return circuit should be given as much attention as the other leads of a circuit. Low impedance paths to aircraft structure are normally required for electronic equipment to provide radio frequency return circuits, and for most electrical equipment to facilitate EMI reduction. Component cases producing electromagnetic energy should be grounded to the structure. All conducting objects on the exterior of the airframe must be bonded through mechanical joints, conductive hinges, or bond straps capable of conducting static charges and lightning strikes. EWIS Identification The proper identification of EWIS components with their circuits and voltages is necessary to provide safe operation and ease of maintenance. Each wire and cable should be marked with a part number and CAGE code so that it can be identified as to its performance capabilities, preventing the inadvertent use of lower performance and unsuitable replacement wire. Unmarked cables are more likely to be reconnected improperly which could cause numerous problems. Best Practices for EWIS The number and complexity of EWIS has resulted in an increased use of electrical connectors for flexibility and modular replacement of electronic equipment. The proper choice and application of connectors is a significant part of the aircraft EWIS system. Connectors should be selected and installed to provide maximum safety and reliability to the aircraft.
• The connector used for each application should be selected only after a careful determination of the electrical and environmental requirements. Consider the size, weight, tooling, logistic, maintenance support, and compatibility with standardization programs. • For ease of assembly and maintenance, connectors using crimped contacts are generally chosen for all applications except those requiring a hermetic seal. • Proper insertion and extraction tools should be used to install or remove wires from connectors. • Connectors susceptible to corrosion may be treated with a chemically inert waterproof jelly, or an environmentally-sealed connector may be used. • Moisture-proof connectors should be used in all zones of the aircraft, including the cabin. Service history indicates that most connector failures occur due to some form of moisture penetration. Even in the pressurized, environmentally-controlled zones of the cockpit and cabin, moisture can occur due to condensation. • Consideration should be given to the design of the pin arrangement to avoid situations where pin-to-pin shorts could result in multiple loss of functions and/or power supplies.
Qwik Connect • April 2019
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