FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 11. Aircraft Electrical Systems | 8. Wiring Installation Inspection Requirements | 11-104. Circuit Breakers
9/27/01
AC 43.13-1B CHG 1
b. Exposed junctions and buses should
be protected with insulating materials. Junc-
tions and buses located within enclosed areas
containing only electrical and electronic
equipment are not considered as exposed.
c. Electrical junctions should be me-
chanically and electrically secure. They should
not be subject to mechanical strain or used as a
support for insulating materials, except for in-
sulation on terminals.
11-104. CIRCUIT BREAKERS. Note
those circuit breakers which have a tendency to
open circuits frequently, require resetting more
than normal, or are subject to nuisance trip-
ping. Before considering their replacement,
investigate the reason.
11-105. SYSTEM SEPARATION. Wires
of redundant aircraft systems should be routed
in separate bundles and through separate con-
nectors to prevent a single fault from disabling
multiple systems. Wires not protected by a
circuit-protective device, such as a circuit
breaker or fuse, should be routed separately
from all other wiring. Power feeders from
separate sources should be routed in separate
bundles from each other and from other air-
craft wiring, in order to prevent a single fault
from disabling more than one power source.
The ground wires from aircraft power sources
should be attached to the airframe at separate
points so that a single failure will not disable
multiple sources. Wiring that is part of elec-
tro-explosive subsystems, such as cartridge-
actuated fire extinguishers, rescue hoist shear,
and emergency jettison devices, should be
routed in shielded and jacketed twisted-pair
cables, shielded without discontinuities, and
kept separate from other wiring at connectors.
To facilitate identification of specific separated
system bundles, use of colored plastic cable
ties or lacing tape is allowed. During aircraft
maintenance, colored plastic cable straps or
lacing tape should be replaced with the same
type and color of tying materials.
11-106. ELECTROMAGNETIC INTER-
FERENCE (EMI). Wiring of sensitive cir-
cuits that may be affected by EMI must be
routed away from other wiring interference, or
provided with sufficient shielding to avoid
system malfunctions under operating condi-
tions. EMI between susceptible wiring and
wiring which is a source of EMI increases in
proportion to the length of parallel runs and
decreases with greater separation. EMI should
be limited to negligible levels in wiring related
to critical systems, that is, the function of the
critical system should not be affected by the
EMI generated by the adjacent wire. Use of
shielding with 85 percent coverage or greater
is recommended. Coaxial, triaxial, twinaxial,
or quadraxial cables should be used, wherever
appropriate, with their shields connected to
ground at a single point or multiple points, de-
pending upon the purpose of the shielding.
The airframe grounded structure may also be
used as an EMI shield.
11-107. INTERFERENCE TESTS. Per-
form an interference test for installed equip-
ment and electrical connections as follow:
a. The equipment must be installed in ac-
cordance with manufacturer’s installation in-
structions. Visually inspect all the installed
equipment to determine that industry standard
workmanship and engineering practices were
used. Verify that all mechanical and electrical
connections have been properly made and that
the equipment has been located and installed in
accordance with the manufacturer’s recom-
mendations. The wire insulation temperature
rating should also be considered.
b. Power input tests must be conducted
with the equipment powered by the airplane’s
electrical power generating system, unless oth-
erwise specified.
Par 11-103
Page 11-49