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PROGRAM TO ENHANCE AIRCRAFT ELECTRICAL WIRING INTERCONNECTION SYSTEM MAINTENANCE
TP 14331 Enhanced Zonal Analysis Procedures 13
• Obstructed drainage holes (in conduits)
(8) Circuit breakers, contactors or relays
• Signs of overheating
• Signs of arcing
c. Wiring installations and areas of concern.
Research has shown that the following installations and areas need to be addressed in
existing maintenance material.
(1) Wiring installations.
Clamping points – Wire chafing is aggravated by damaged clamps, clamp cushion migration,
or improper clamp installations. Aircraft manufacturers specify clamp type and part number
for EWIS throughout the aircraft. When replacing clamps use those specified by the aircraft
manufacturer. Tie wraps provide a rapid method of clamping especially during line
maintenance operations. Improperly installed tie wraps can have a detrimental effect on wire
insulation. When new wiring is installed as part of a STC, or modification the drawings will
provide wiring routing, clamp type and size, and proper location. Examples of significant
wiring modifications are the installation of new avionics systems, new galley installations and
new instrumentation. Wire routing, type of clamp and clamping location should conform to
the approved drawings. Adding new wire to existing wire bundles may overload the clamps
causing wire bundle to sag and wires to chafe. Raceway clamp foam cushions may deteriorate
with age, fall apart, and consequently would not provide proper clamping.
Connectors – Worn environmental seals, loose connectors, missing seal plugs, missing
dummy contacts, or lack of strain relief on connector grommets can compromise connector
integrity and allow contamination to enter the connector, leading to corrosion or grommet
degradation. Connector pin corrosion can cause overheating, arcing and pin-to-pin shorting.
Drip loops should be maintained when connectors are below the level of the harness and tight
bends at connectors should be avoided or corrected.
Terminations – Terminations, such as terminal lugs and terminal blocks, are susceptible to
mechanical damage, corrosion, heat damage and contamination from chemicals, dust and dirt.
High current-carrying feeder cable terminal lugs can over time lose their original torque value
due to vibration. One sign of this is heat discoloration at the terminal end. Proper build-up
and nut torque is especially critical on high current carrying feeder cable lugs. Corrosion on
terminal lugs and blocks can cause high resistance and overheating. Dust, dirt and other debris
are combustible and therefore could sustain a fire if ignited from an overheated or arcing
terminal lug. Terminal blocks and terminal strips located in equipment power centers (EPC),
avionics compartments and throughout the aircraft need to be kept clean and free of any
combustibles.
PROGRAM TO ENHANCE AIRCRAFT ELECTRICAL WIRING INTERCONNECTION SYSTEM MAINTENANCE
TP 14331 Enhanced Zonal Analysis Procedures 14
Backshells – Wires may break at backshells, due to excessive flexing, lack of strain relief, or
improper build-up. Loss of backshell bonding may also occur due to these and other factors.
Sleeving and Conduits – Damage to sleeving and conduits, if not corrected, may lead to wire
damage. Therefore, damage such as cuts, dents and creases on conduits may require further
investigation for condition of wiring within.
Grounding Points – Grounding points should be checked for security (i.e., finger tightness),
condition of the termination, cleanliness, and corrosion. Any grounding points that are
corroded or have lost their protective coating should be repaired.
Splices – Both sealed and non-sealed splices are susceptible to vibration, mechanical damage,
corrosion, heat damage, chemical contamination, and environmental deterioration. Power
feeder cables normally carry high current levels and are very susceptible to installation error
and splice degradation. All splices should conform to the TC or STC holder’s published
recommendations. In the absence of published recommendations, environmental splices are
recommended to be used.
(2) Areas of concern.
Wire Raceways and Bundles – Adding wires to existing wire raceways may cause undue
wear and chafing of the wire installation and inability to maintain the wire in the raceway.
Adding wire to existing bundles may cause wire to sag against the structure, which can cause
chafing.
Wings – The wing leading and trailing edges are areas that experience difficult environments
for wiring installations. The wing leading and trailing edge wiring is exposed on some aircraft
models whenever the flaps or slats are extended. Other potential damage sources include slat
　
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