FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 11. Aircraft Electrical Systems | 15. Grounding and Bonding | 11-186. Grounding
9/27/01
SECTION 15. GROUNDING AND BONDING AC 43.13-1B CHG 1
11-185. GENERAL. One of the more im
portant factors in the design and maintenance
of aircraft electrical systems is proper bonding
and grounding. Inadequate bonding or
grounding can lead to unreliable operation of
systems, e.g., EMI, electrostatic discharge
damage to sensitive electronics, personnel
shock hazard, or damage from lightning strike.
This section provides an overview of the prin
ciples involved in the design and maintenance
of electrical bonding and grounding.
SAE ARP-1870 provides for more complete
detailed information on grounding and bond
ing, and the application of related hardware.
11-186. GROUNDING. Grounding is the
process of electrically connecting conductive
objects to either a conductive structure or some
other conductive return path for the purpose of
safely completing either a normal or fault cir
cuit.
a. Types of Grounding. If wires carrying
return currents from different types of sources,
such as signals of DC and AC generators, are
connected to the same ground point or have a
common connection in the return paths, an in
teraction of the currents will occur. Mixing
return currents from various sources should be
avoided because noise will be coupled from
one source to another and can be a major
problem for digital systems. To minimize the
interaction between various return currents,
different types of grounds should be identified
and used. As a minimum, the design should
use three ground types: (1) ac returns, (2) dc
returns, and (3) all others. For distributed
power systems, the power return point for an
alternative power source would be separated.
For example, in a two-ac generator (one on the
right side and the other on the left side) sys
tem, if the right ac generator were supplying
backup power to equipment located in the left
side, (left equipment rack) the backup ac
ground return should be labeled “ac Right”.
The return currents for the left generator
should be connected to a ground point labeled
“ac Left”
b. Current Return Paths. The design of
the ground return circuit should be given as
much attention as the other leads of a circuit.
A requirement for proper ground connections
is that they maintain an impedance that is es
sentially constant. Ground return circuits
should have a current rating and voltage drop
adequate for satisfactory operation of the con
nected electrical and electronic equipment.
EMI problems, that can be caused by a sys
tem’s power wire, can be reduced substantially
by locating the associated ground return near
the origin of the power wiring (e.g. circuit
breaker panel) and routing the power wire and
its ground return in a twisted pair. Special care
should be exercised to ensure replacement on
ground return leads. The use of numbered in
sulated wire leads instead of bare grounding
jumpers may aid in this respect. In general,
equipment items should have an external
ground connection, even when internally
grounded. Direct connections to a magnesium
(which may create a fire hazard) structure must
not be used for ground return.
c. Heavy-Current Grounds. Power
ground connections, for generators, trans
former rectifiers, batteries, external power re
ceptacles, and other heavy-current, loads must
be attached to individual grounding brackets
that are attached to aircraft structure with a
proper metal-to-metal bonding attachment.
This attachment and the surrounding structure
must provide adequate conductivity to ac
commodate normal and fault currents of the
system without creating excessive voltage drop
or damage to the structure. At least three fas
teners, located in a triangular or rectangular
pattern, must be used to secure such brackets
Par 11-185
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