General Electrical Bonding - Garmin GTX 335 w GPS Installation Guidance

3.15 General Electrical Bonding

NOTE
The reconditioned value in table 3-13 is for installation. During service life checks, the
periodic test value is used. If the maintenance check shows resistance above the periodic
test value, the bonding must be improved to reach the reconditioned value.
Electrical equipment chassis, shield/ground terminations, antennas, supporting brackets, and racks must be
electrically bonded to the aircraft's ground reference as shown in table 3-13. Refer to section 5 of SAE
ARP1870 when surface preparation is required to achieve electrical bond. The electrical bond must
achieve direct current (DC) resistance less than or equal to the reconditioned value shown in table 3-13 for
the aircraft type and model.
For some aircraft the instrument panel is attached with vibration mounts. For these aircraft it must be
verified that the vibration-isolated instrument panel is grounded to the airframe metallic structure with a
bonding jumper the same or equivalent to the specification below. If a jumper is not installed, a bonding
strap with this criteria must be installed:
The cross sectional area of the strap must be greater than 0.016 sq inches (approx 20800 circular
mils). A 7/16-inch or wider tubular braid (QQB575R30T437, 24120 circular mils) or a ¾-inch or
wider flat braid (QQB575F36T781, 20,800 circular mils) must be used.
The strap length should be as short as possible and must not exceed six inches in length. Detailed
design of a bonding strap meeting these requirements is shown in section 3.
Electrical bonding must be verified by inspection using a calibrated milliohm meter. Refer to section 3. An
equivalent OEM procedure can also be substituted.
Brackets installed to the main aircraft metallic structure with four or more rivets can provide sufficient
electrical bond to allow equipment chassis or install rack to be bonded to the bracket.
The correct material finish is important when mating untreated or bare dissimilar metals. Materials should
be galvanically-compatible. When corrosion protection is removed to make an electrical bond, any
exposed area after the bond should be protected again.
Additional guidance is found in AC 43.13-1B and SAE ARP 1870. Refer to figure 3-3, figure 3-4, and
figure 3-5 for typical electrical bonding preparation examples.
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GTX 335 w/GPS Installation Guidance
Page 3-15