Chapter 11 | Corrosion | Electrical Conductor

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Chapter 11
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  9/8/98AC 43.13-1BPar 11-189Page 11-75 11-189.   BONDING JUMPER INSTAL-LATIONS.  Bonding jumpers should be madeas short as practicable, and installed in such amanner that the resistance of each connectiondoes not exceed .003 ohm. The jumper should not interfere with the operation of movableaircraft elements, such as surface controls, nor should normal movement of these elements re-sult in damage to the bonding jumper. a.   Bonding Connections. To ensure alow-resistance connection, nonconducting fin-ishes, such as paint and anodizing films,should be removed from the attachment sur-face to be contacted by the bonding terminal.On aluminum surfaces, a suitable conductivechemical surface treatment, such as Alodine,should be applied to the surfaces within24 hours of the removal of the srcinal finish.Refer to SAE, ARP 1870 for detailed instruc-tions. Electric wiring should not be grounded directly to magnesium parts. b.   Corrosion Protection. One of themore frequent causes of failures in electricalsystem bonding and grounding is corrosion.Aircraft operating near salt water are particu-larly vulnerable to this failure mode. Because bonding and grounding connections may in-volve a variety of materials and finishes, it isimportant to protect completely against dis-similar metal corrosion. The areas around completed connections should be post-finished in accordance with the srcinal finish require-ments or with some other suitable protectivefinish within 24 hours of the cleaning process.In applications exposed to salt spray environ-ment, a suitable noncorrosive sealant, such asone conforming to MIL-S-8802, should beused to seal dissimilar metals for protectionfrom exposure to the atmosphere. c.   Corrosion Prevention. Electrolyticaction may rapidly corrode a bonding connec-tion if suitable precautions are not taken.Aluminum alloy jumpers are recommended for most cases; however, copper jumpers should  be used to bond together parts made of stain-less steel, cadmium plated steel, copper, brass,or bronze. Where contact between dissimilar metals cannot be avoided, the choice of jumper and hardware should be such that corrosion isminimized, and the part likely to corrodewould be the jumper or associated hardware.Tables 11-14 through 11-16 and figures 11-20through 11-22 show the proper hardware com- binations for making a bond connection. Atlocations where finishes are removed, a pro-tective finish should be applied to the com- pleted connection to prevent subsequentcorrosion. d.   Bonding Jumper Attachment . Theuse of solder to attach bonding jumpers should  be avoided. Tubular members should be bonded by means of clamps to which the jumper is attached. Proper choice of clampmaterial should minimize the probability of corrosion. e.   Ground Return Connection. When bonding jumpers carry substantial ground re-turn current, the current rating of the jumper should be determined to be adequate and thata negligible voltage drop is produced. 11-190.   CREEPAGE DISTANCE.  Careshould be used in the selection of electricalcomponents to ensure that electrical clearanceand creepage distance along surfaces betweenadjacent terminals, at different potentials, and  between these terminals and adjacent ground surfaces are adequate for the voltages in-volved.
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