NBAA Conference 2003 1

Massoud Sadeghi: massoud.sadeghi@faa.gov

FAA Aging Systems Program Manager

Transport Airplane Directorate; ANM-117(425)227-2117

Brett Portwood: brett.portwood@faa.gov

FAA Technical Specialist for Safety and integration

Los Angeles ACO; ANM-130L(562)627-5350

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Topic Outline

Electrical load determinationBreaker and wire sizing/selectionRouting/clamping/bend radiiSplicingWire terminalsGrounding and bondingWire markingConnectors and conduitsWire insulation properties

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Electrical Load Determination

Load analysis

New or additional electrical devices should not be installed without an electrical load analysis (AC 43.13-1b)

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AC 43.13-1b Topic Outline, cont.

Electrical load determination

Breaker and wire sizing/selection

Routing/clamping/bend radiiSplicingWire terminalsGrounding and bondingWire markingConnectors and conduitsWire insulation properties

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Circuit Breaker Protection

“A circuit breaker must always open before any component downstream can overheat and generate smoke or fire.” (AC 43.13-1b, para. 11-48)

“Circuit breakers are designed as circuit protection for the wire, not for protection of black boxes or components . . .” (AC 43.13-1b, para. 11-51)

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Circuit Breaker Protection, cont.

Use of a circuit breaker as a switch is not recommended

Repeated opening and closing of contacts can lead to damage and premature failure of circuit breakers

Most circuit breaker failures are latent

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Wire Selection

Size wires so they:Have sufficient mechanical strength

Do not exceed allowable voltage drop levels

Are protected by circuit protection devices

Meet circuit current-carrying requirements

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Wire Selection, cont.

Mechanical strength of wire sizes less than #20

Do not use wire with less than 19 strandsProvide additional support at terminationsShould not be used when subject to excessive vibration, repeated bending, or frequent disconnection

(ref. para. 11-66(a), page 11-21)

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AC 43.13-1b Topic Outline, cont.

Electrical load determinationBreaker and wire sizing/selection

Routing/clamping/bend radii

SplicingWire terminalsGrounding and bondingWire markingConnectors and conduitsWire insulation properties

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Wiring Routing

Eliminate potential for chafing against structure or other components

Position to eliminate/minimize use as handhold or support

Minimize exposure to damage by maintenance crews or shifting cargo

Avoid battery electrolytes or other corrosive fluids

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Wire Riding on Structure

Power cables riding on structure can

cause damage to the power cables

A

B

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Wires Riding on Other Wires

Wire bundles that Wire bundles that cross should be cross should be

secured together to secured together to avoid chafingavoid chafing

B

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Wires Riding on Other Wires

B

Wire bundles that Wire bundles that cross should be cross should be

secured together as secured together as shownshown

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Wires Riding on Lightening Hole

If the wire is not If the wire is not supported and supported and

grommet is too short, grommet is too short, then there is wire then there is wire bundle chafingbundle chafing

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Wires Properly Installed on Lightening Hole

Wires supported and Wires supported and proper grommet proper grommet

installationinstallation

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Wiring as a Handhold

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Wiring Routing, cont.

Protect wires in wheel wells and other exposed areas

Route wires above fluid lines, if practicable

Use drip loops to control fluids or condensed moisture

Keep slack to allow maintenance and prevent mechanical strain

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Path of exposed end

Broken wire shall not make contact with fluid line

Wire Bundles Above Fluid Lines

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Wires improperly tied, riding on hydraulic lines,

contaminated with caustic fluid

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Wire bundle breakout

Figure 8 loop may be located before or after tail of Y

Plastic mechanical strapping

Wire bundles

Before

After

Y Type Wire Bundle Breakouts

Head of strap shall not be located in this area or touching anything to cause chafing

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Plastic mechanical strapping

Wire bundle breakout

Wire bundle

Head of strap shall not be located in

this area or touching anything

to cause chafing

T Type Wire Bundle Breakouts

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Complex TypeWire Bundle Breakouts

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Stand-offs

Use stand-offs to maintain clearance between wires and structure

Employing tape or tubing is generally notnot acceptable as an alternative

Exception:Exception: Where impossible to install off-angle clamps to maintain wiring separation in holes, bulkheads, floors, etc.

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Exercise: Using Stand-offs

A

B

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Bundle riding on structure

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Wire bundle riding on control cable

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Clamping

Support wires by suitable clamps, grommets, or other devices at intervals of not more that 24 inches

Supporting devices should be of suitable size and type with wire and/or cables held securely in place without damage to wire or wire insulation

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Clamps

Wire bundles should be snug in clamp (no movement)

Cable not able to move axially

RF cables: Do Not Crush

Mount clamps with attachment hardware on top

Tying not to be used as alternative to clamping

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Example of Correct Cable Slack

Appropriate slack

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Clamp Distortion

Incorrect clamp position

Distortion of rubber on clamp is NOT acceptable

Correct clamp position

WF2