7.7 Electrical Wiring Interconnection
System (EWIS)
Electrical equipment should never be operated in areas where explosive vapors are
present or suspected, unless the equipment has what properties? - ANS explosion
proof and designed specifically for use in such areas.
If it is necessary to work on energized circuits or on live electrical equipment what
should we make sure to use and do? - ANS always use adequate protective materials
and take extreme care.
When preparing to work on de-energised electrical circuits what 3 things must we
ensure? - ANS • The external power switch is off.
• The battery is disconnected.
• Red safety tags are fitted.
What causes electric shock and burns? - ANS Current does the damage, not the
voltage
In fuel tanks or flammable vapour areas what mustn't we use? - ANS Never use electric
tools which deliver more than 0.02 millijoules of energy or heat generating tools.
In fuel tanks or flammable vapour areas what should we use? - ANS Only crimped
contacts, terminals, splices and non-heat shrinkable sleeves are to be used in these
areas.
What should the wiring installation conform to? (In order of importance) - ANS • 1st -
Flight safety.
• 2nd - Ease of maintenance, removal and replacement of parts.
• 3rd - Cost effective aircraft production and repair.
How far should wire bundles run from lines carrying flammable liquid such as fuel,
hydraulic oil, oxygen ect? - ANS 50mm(1.9inch)
What's the minimum bend radius for single wires and cables? - ANS 3 times the
outside diameter
, What's the preferred value for bend radius of a single wire or cable? - ANS 10 times the
outside diameter
What's the smallest bend radius for a wire bundle? - ANS 6 times the outside diameter
What's the minimum bend radius for single coax cables and wire bundles with coax
cables attached? - ANS 10 times the outside diameter of the coax cable
What checks must you do each time a wire is added, repaired or reconnected? - ANS
The wire is in the plug (give a light tug) and a continuity and functional check.
Wire bundles in the fuselage must be clamped how often? - ANS At every frame
When a wire bundle is dressed downwards to a connector what must we do? - ANS
Include a drip loop to avoid contamination
How is an overbraided shield wire identified? - ANS A W number within 18 inches of all
connectors and at every six feet
What precaution do we take with essential system wires? - ANS Separate them by
space
Cable clamps spacing? - ANS Not exceeding 24 inches
What must we wrap aromatic polyimide wires in? - ANS Insulation tape prior to
clamping to prevent damage to the insulation
Wire harnesses are not permitted to do what? - ANS Turn in a block clamp and move
When do we fit grommets or strips? 2 cases - ANS Where physical separation of at
least 3/8 inch cannot be maintained or if the clearance between the wires and the edges
of the hole is less than 1/4.
When installing clamps where should the mounting screw be? - ANS Above the wire
bundle and back of clamp rests with the structural member
What do we use to fill the space between wires and cables ? - ANS Using coil or star
spacers
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