The use of Kapton as electrical wire insulation dates back to 1970. Since then, DuPont continues to supply Kapton wire to Airplane manufacturers globally. However, an event almost led to the collapse of this partnership.
On September 2, 1998, an MD-11, Swissair Flight 111, crashed into the Atlantic Ocean, killing all 229 on-board. Investigations into the matter attribute the crash to loss of control due to an in-flight fire. Additionally, the cause of the fire stems from the faulty wiring in the plane’s in-flight entertainment system. Furthermore, the evidence shows the wire insulation contributing to the fire that led to the catastrophic crash.
Thus, the Transport Safety Board of Canada and the US Federal Aviation Administration made nine safety changes. This changed the testing, certification, inspection, and maintenance of plane materials. Most notably is the impact of these changes on Kapton insulated wire for the electrical works in both civilian and military aircraft. So, is Kapton wire safe?
What are Kapton Wires?
Swissair plane in flight
Firstly, electrical connections can feature either aluminum or copper wires. Furthermore, the type of insulation will depend on their operating environment. As such, you will find industry insiders referring to wire types by the type of insulation they employ.
Kapton wires are copper wires that feature a polyimide film that allows the conductor to operate across a vast temperature range. Additionally, the excellent dielectric properties, incredible malleability, and low outgassing rate see Kapton wires in use across many places. For instance in airplanes, space crafts, and 3D printers.
In the late 1960s, American chemical company DuPont released Kapton as one of its revolutionary polymer products. For instance, they released nylon, Teflon, and Neoprene. Also, the polymer results from the condensation of 4,4-oxydiphenylene and pyromellitic dianhydride. This happens during a process called polymerization. The final product is an aromatic lightweight insulation material. The material can accommodate a temperature range from zero to four hundred degrees Celsius. So, every electrician prefers Kapton wires for installations. This is especially where resistance to temperature, weight, and flexibility are mandatory.
Common Concerns About Kapton Wires?
Concerns about Kapton wires in aircraft electronic systems began long before the Swissair flight 111 incident. For example, the high frequency of in-flight fires and military aircraft crashes due to malfunctioning electrical wires in the 1980s led the US military to conduct studies on the use of Kapton insulated wire. Subsequently, the studies reveal the following disadvantages of using Kapton insulated wire.
Charred electrical wires.
Charring refers to a situation where the wire insulation burns following an electric short. As such, it changes to form a carbon residue that compromises the wire’s integrity. Kapton wires feature a combination of copper wire strands. They also have an aromatic polyimide acting as the insulation material. In addition, the thickness of the Kapton insulation varies depending on the type of airplane electrical equipment.
Results from the studies reveal that a Kapton insulated wire tends to be more susceptible to charging than other wire types. Furthermore, the resultant carbon residue is both conductive and flammable. Therefore, any surge in the electric current can cause the entire system to ignite, as was the case in Swissair Flight 111.
Man holding arcing electrical wires.
Arcing involves a situation where the current jumps between connections rather than flowing through the conductor. Additionally, it occurs where there is damage to the wire insulation through charring or mechanical wear. As a result, an electric charge from the exposed conductor can jump from one conducting surface to another. Furthermore, the flashes of electricity can reach temperatures as high as 19,500 degrees Celsius, enough to cause a fire.
Keeping this in mind, Kapton insulated electrical wiring experiences a high degree of abrasion within cable harnesses. This is a result of aircraft movement. As such, the polyamide polymer insulation breaks, exposing the copper wire within. As a result, it increases the possibility of arcing occurring.
Investigations into airplane accidents from 1980 to 1999 indicate that charring and arcing of the Kapton insulated electrical wiring led to a fire destroying the planes’ entire wire bundle. Consequently, there was a significant loss of control, allowing the crashes to happen.
So, What are the Best Solutions to Kapton Wire Failures?
Complete rewiring overhaul program
Rewiring of an aircraft’s control panel
The best way to mitigate the impending danger from Kapton insulated wiring is to replace the existing wiring. Aviation authorities globally mandate both airplane manufacturers and operators to replace their existing Kapton wiring with safer alternatives. For example, the US military now uses the TKT insulated wire in their AH1-Cobras and F-15C/D aircraft. Similarly, all Boeing planes from 1992 also use the new TKT polyimide polymer wrapping for all their airplane wiring.
A separate emergency electrical system
MD-11 airplane on the taxiway
Alternatively, you can also install a separate emergency electrical system in your aircraft to provide safe emergency power when there is an electrical fire. The consensus among aviation authorities is the Virgin Electrical Bus, which utilizes a separate battery and air-driven generator to power the vital controls during electric fire emergencies.
How Do You Determine the Health of a Kapton Wire?
Like with all lab-produced products, polyimide materials degrade over time. In addition, the degradation can lead to drastic consequences, including the destruction of equipment or death, as in the case of Kapton insulated electrical wiring in planes.
Scientists checking the viscosity of a polymer
DuPont recommends the Inherent Viscosity Test as the best way to determine the health of a Kapton wire. It involves measuring the molecular weight of different layers of polyimide. Then, comparing the results to DuPont’s minimum molecular weight measure. Accordingly, you can schedule your monitoring, maintenance, and rewiring programs, to ensure the proper functioning of your electrical installations. For example, 2016 saw the US military conduct IVT testing on 300 aircraft as part of their Electrical Wire Interconnection System Service Life Extension Program.
So, is Kapton wire safe? Despite a shaky debut, Kapton wires continue to feature in many electrical works. For example, the KK-J-24s-SLE-100 wire features a Kapton Tape Wrap as insulation. Electricians use it as medical wire in many laboratory electric works. Finally, you can learn more about Kapton wires and IVT services by contacting Cloom’s representatives.