Piper Comanche PA-24 Service Manual page 224

4-43a. Electrical Bonding
A. General
All electrical and electronic equipment and specified components shall be installed in such a
manner as to provide a continuous low resistance path (bonds) from the equipment
enclosure/component to the airplane structure. Bonds must be installed to ensure that the structure
and equipment are electrically stable and free from the hazards of lightning, static discharge,
electrical shock, etc.
1. All parts shall be bonded with as short a lead as possible.
2. All bonding surfaces shall be cleaned prior to the installation of the bonded joint.
3. All nuts used in bonding shall be of the self-locking type. (Do Not use fiber-locking type).
4. All electrical bonding shall be accomplished without affecting the structural integrity of the
airframe.
B. 100 Hour Inspection
Each 100 hours, visually inspect shield and shield terminations of each electrical harness for
integrity, condition, and security. If electrical arcing is evident, check for intermittent contact
between conducting surfaces. Arcing can be prevented by bonding or insulation, as appropriate.
Inspect the components listed in Table IV-III as follows:
1. Bond connections shall be secure and free from corrosion.
2. Bonding jumpers installed so as not to interfere in any way with the operation of moveable
components of the aircraft.
3. No self-tapping screws used for bonding purposes.
4. Exposed conducting frames or parts of electrical or electronic equipment should have a low
resistance bond of less than 2.5 millohms to structure. If the equipment design includes a
ground terminal or pin, which is internally connected to such exposed parts, a ground wire
connection to such terminal will satisfy this requirement.
5. Parts shall be bonded directly to the primary structure rather than to other bonded parts.
6. Where aluminum or copper is bonded to dissimilar metallic structures, ensure installed
hardware (typically washers) is as called out in the parts catalog to minimize electrolytic
corrosion and ensure the hardware should corrode first.
C. On Condition Inspection
Whenever any electrically bonded component (see Table IV-III) is removed and reinstalled, or
visual inspection reveals the electrical bonding to be suspect, measure resistance between
component and aircraft structure.
To ensure proper operation and suppression of radio interference from hazards, electrical bonding
of equipment must not exceed the maximum allowable resistance values specified in Table IV-III.
1. Measurements should be performed after the grounding and bonding mechanical connections
are complete to determine if the measured resistance values meet the basic requirements.
2. A high quality test instrument (AN/USM-21A or equivalent) will accurately measure the very
low resistance values specified.
3. Another method of measurement is the millivolt drop test as shown in Figure 4-7a.
IV - STRUCTURES
PIPER SENECA SERVICE MANUAL
1E18D
(PIR-PPS55006, Rev. Z)
(PIR-AC 43.13-1, Rev. B.)
04/01/09