Equipment Bonding; Table 4-1 Bonding Requirements - Garmin GI 275 Installation Manual

4.2 Equipment Bonding

All installed items listed in Table 4-1 must be electrically bonded to the same airframe ground plane and
meet the listed milliohm requirement. The resistance must be verified with a calibrated milliohm meter
with ±0.1 Ω (or better) accuracy with all connector(s) disconnected.
m
All existing third-party remote equipment interfaced to a GI 275 must be electrically bonded to the
airframe ground. It is not acceptable to interface the GI 275 equipment to existing third-party equipment
that relies only on power ground return wires as an electrical ground.
Electrical bonding can be achieved with mounting hardware (e.g., rivets, bolts, nuts, washers, etc.) or via
bond straps. Bonding surfaces must be clean of any primer, grease, or dirt. If mounting hardware is used to
create the electrical bond, the area under the head of the bolt or washer must be free of primer and a spot
face prepared that is at least 0.125 inches wider than the head of the bolt or the washer. Any exposed area
still visible after the bond is completed must be primed and finished with the original coating or other
suitable film. Rivets used to mechanically attach brackets and shelves provide an inherent electrical bond
through the rivets and require no additional bond preparation. The top or bottom side of the Garmin racks
or equipment flanges do not need any special bond preparations. Reference the aircraft manufacturer
(electrical) standard practices manual for procedures on electrical bond preparation, or follow SAE ARP
1870 Aerospace Systems Electrical Bonding and Grounding for Electromagnetic Compatibility and Safety,
Section 5, Detail Requirements.
Unit
GI 275 Base
Engine Annunciator(s)
GEA 24
GTP 59
GSB 15
The instrument panel must be metal construction allowing a ground path for instrument panel installations.
For metal and tube-and-fabric aircraft, the ground path is inherently achieved through the metallic airframe
structure. For composite aircraft, a ground plane (or reference) must be used to achieve a comparable
ground.
The face sheet on honeycomb shelves must be metal when equipment is mounted to the shelf. The
honeycomb material between the face sheets is not conductive; therefore, care must be taken to ensure
proper bonding of the equipment. The top and bottom face sheets must be grounded to each other and at
least one of face sheets must be grounded to the airframe.
190-02246-14
Rev. 11

Table 4-1 Bonding Requirements

Ω (from unit to instrument panel)
2.5 m
Ω (from unit to instrument panel)
10 m
Ω (from unit to local structure)
2.5 m
Ω or electrically isolated per Appendix D (from
2.5 m
unit to local structure)
Ω (from unit to instrument panel or local
2.5 m
structure)
Value
GI 275 STC EIS & MFD Installation Manual
Page 4-5