Bonding is defined as the electrical connecting of two or more conducting objects that are not already securely connected, while grounding consists of forming an electrical connection between the conducting object and the primary structure for return of current. For context, the primary structure encompasses the main frame, fuselage, or wing structure of the aircraft. Some of the main reasons bonding and grounding connections are made in aircraft electrical systems are to protect aircraft and personnel against hazards from lightning discharge, provide current return paths, prevent the development of radio-frequency potentials, protect personnel from shock hazard, stabilize radio transmission and reception, and prevent the build-up of static charge.
When dealing with electrical components, one must be meticulous. As such, we will outline some general procedures and precautions to take when carrying out bonding or grounding connections. First, you must ensure that the areas where the bonding or grounding connections are being made are practical. In addition to this, the connection should not compromise the integrity of the aircraft and should only be installed on smooth, clean surfaces. Second, parts should always be bonded individually, if possible. Next, bonding or ground connections should be secure enough so that vibration, expansion, or contraction does not break or loosen the connection. While this may go without saying, such connections should be installed in protected areas.
Bonding jumpers should always be kept short and tight, so that the resistance of each connection does not surpass 0.003 ohm. More than that, the jumper should not get in the way of other movable aircraft elements like surface controls. Similarly, the normal movement of these elements should not damage the bonding jumper. To ensure a low resistance connection is achieved, nonconducting finishes, such as paint and anodizing films, should be removed from the surface. It is important to note that electrolytic action can quickly corrode a bonding connection if precautions are not taken during installation. For this reason, aluminum alloy jumpers are recommended, but copper jumpers can also be used to bond parts made of stainless steel, cadmium-plated steel, copper, brass, or bronze.
When contact is made between dissimilar metals, the choice of jumper and hardware relies on the need for minimal corrosion. In regions where finishes are removed, a protective finish should be applied to the connection to prevent corrosion. In addition, avoid solder to attach bonding jumpers. Tubular members should be bonded with the help of clamps where the jumper is attached. With the proper clamp material, the probability of corrosion can be minimized. Keep in mind that bonding jumpers carry a substantial amount of ground return current, the current rating of the jumper should be sufficient and it should be determined that a negligible voltage drop is generated.
A bonding and grounding connection is generally achieved on a flat surface with the help of through-bolts or screws where there is an ease-of-installation. There are a few common bolted connections, each of which differs based on the application’s needs. For instance, to make a stud connection, a bolt or screw is securely locked to the structure becoming a stud. With this connection type, ground or bonding jumpers can be removed or added to the shank of the stud without removing the stud from the structure. Meanwhile, nutplates are welded or riveted in areas where access to the nut for repairs is difficult. Lastly, the hardware used to make bonding or grounding connections should be chosen based on its mechanical strength and current to be carried.
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