FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 11. Aircraft Electrical Systems | 3. Inspection of Equipment Installation | 11-37. Junction Box Construction
9/27/01
AC 43.13-1B CHG 1
data should provide a true picture of the status
of the electrical system. New or additional
electrical devices should not be installed in an
aircraft, nor the capacity changed of any power
source, until the status of the electrical system
in the aircraft has been determined accurately
and found not to adversely affect the integrity
of the electrical system.
11-37. JUNCTION BOX CONSTRUC-
TION. Replacement junction boxes should be
fabricated using the same material as the origi-
nal or from a fire-resistant, nonabsorbent mate-
rial, such as aluminum, or an acceptable plastic
material. Where fire-proofing is necessary, a
stainless steel junction box is recommended.
Rigid construction will prevent “oil-canning”
of the box sides that could result in internal
short circuits. In all cases, drain holes should
be provided in the lowest portion of the box.
Cases of electrical power equipment must be
insulated from metallic structure to avoid
ground fault related fires. (See para-
graph 11-7.)
c. Wiring. Junction box layouts should
take into consideration the necessity for ade-
quate wiring space and possible future addi-
tions. Electrical wire bundles should be laced
or clamped inside the box so that cables do not
touch other components, prevent ready access,
or obscure markings or labels. Cables at en-
trance openings should be protected against
chafing by using grommets or other suitable
means.
11-38.11-46. [RESERVED.]
a. Internal Arrangement. The junction
box arrangement should permit easy access to
any installed items of equipment, terminals,
and wires. Where marginal clearances are un-
avoidable, an insulating material should be in-
serted between current carrying parts and any
grounded surface. It is not good practice to
mount equipment on the covers or doors of
junction boxes, since inspection for internal
clearance is impossible when the door or cover
is in the closed position.
b. Installation. Junction boxes should be
securely mounted to the aircraft structure in
such a manner that the contents are readily ac-
cessible for inspection. When possible, the
open side should face downward or at an angle
so that loose metallic objects, such as washers
or nuts, will tend to fall out of the junction box
rather than wedge between terminals.
Par 11-38
Page 11-13 (and 11-14)