Bonding is the electrical connecting of two or more  conducting objects not otherwise adequately connected. The following bonding requirements must be considered: Bonding jumpers should be made as short as practicable, and  installed in such a manner that the resistance of each connection  does not exceed .003 ohm. The jumper should not interfere  with the operation of movable aircraft elements, such as surface  controls, nor should normal movement of these elements result  in damage to the bonding jumper.  [Figure 9-145] 9-87 •  Ground return connection—when bonding jumpers  carry substantial ground return current, the current  rating of the jumper should be determined to be  adequate, and a negligible voltage drop is produced.  [Figure 9-146] •  Bonding jumper attachment—the use 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 clamp  material should minimize the probability of corrosion. •  Corrosion prevention—electrolytic action may  rapidly corrode a bonding connection 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 stainless 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 is minimized;  the part likely to corrode should be the jumper or  associated hardware. •  Static bonds—all isolated conducting parts inside  and outside the aircraft, having an area greater than 3  square inches and a linear dimension over 3 inches,  that are subjected to appreciable electrostatic charging  due to precipitation, fluid, or air in motion, should  have a mechanically secure electrical connection to the  aircraft structure of sufficient conductivity to dissipate  possible static charges. A resistance of less than 1 ohm  when clean and dry generally ensures such dissipation  on larger objects. Higher resistances are permissible  in connecting smaller objects to airframe structure. •  Corrosion protection—one of the more frequent  causes of failures in electrical system bonding and  grounding is corrosion. The areas around completed  connections should be post-finished quickly with a  suitable finish coating. •  Bonding connections—to ensure a low-resistance  connection, nonconducting finishes, such as paint  and anodizing films, should be removed from the  attachment surface to be contacted by the bonding  terminal. Electrical wiring should not be grounded  directly to magnesium parts. •  Metallic surface bonding—all conducting objects  on the exterior of the airframe must be electrically  connected to the airframe through mechanical joints,  conductive hinges, or bond straps capable of conducting  static charges and lightning strikes. Exceptions may be  necessary for some objects, such as antenna elements,  whose function requires them to be electrically isolated  from the airframe. Such items should be provided with  an alternative means to conduct static charges and/or  lightning currents, as appropriate. •  Equipment bonding—low-impedance paths to  aircraft structure are normally required for electronic  equipment to provide radio frequency return circuits  and for most electrical equipment to facilitate reduction  in EMI. The cases of components that produce  electromagnetic energy should be grounded to structure.  To ensure proper operation of electronic equipment,  it is particularly important to conform the system’s  installation specification when interconnections,  bonding, and grounding are being accomplished. Figure 9-145.  Bonding jumpers. Bonding Testing of Bonds and Grounds Bonding Jumper Installation The resistance of all bond and ground connections should  be tested after connections are made before re-finishing. The  resistance of each connection should normally not exceed  0.003 ohm. A high quality test instrument, an AN/USM-21A  or equivalent, is required to accurately measure the very low  resistance values. 