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An Apparatus for Monitoring the Health of Electrical Cables D. M. Pai1, Paul F. Tatum2 and M. J. Sundaresan1 1 Center for Advanced Materials and Smart Structures 2 Undergraduate Research Assistant, Intelligent Structures and Mechanisms Lab Dept of Mechanical Engineering North Carolina A&T State University Greensboro, NC 27411

Introduction As with most elements of infrastructure, electrical wiring is innocuous; usually hidden away and unnoticed until it fails. Failure of infrastructure, however, sometimes leads to serious health and safety hazards. Electrical wiring fails when the polymeric (usually rubber) insulation material that sheathes the conductor gets embrittled with age from exposure to pressure, temperature or radiation cycling or when the insulation gets removed by the chafing of wires against each other. Miles of such wiring can be found in typical aircraft, with significant lengths of the wiring immersed in aviation fuel – a recipe for an explosion if a spark were to occur. Diagnosing the health of wiring is thus an important aspect of monitoring the health of aging aircraft. Stress wave propagation through wiring affords a quick and non-invasive method for health monitoring. The extent to which a stress wave propagating through the cable core gets attenuated depends on the condition of the surrounding insulation. When the insulation is in good condition – supple and pliable, there is more damping or attenuation of the waveform. As the insulation gets embrittled and cracked, the attenuation is likely to reduce and the waveform of the propagating stress wave is likely to change. The monitoring of these changes provides a potential tool to evaluate wiring or cabling in service that is not accessible for visual inspection. This experiment has been designed for use in an introductory mechanical or materials engineering instrumentation lab. Initial setup (after procuring all the materials) should take the lab instructor about 4 hours. A single measurement can be initiated and saved to disk in less than 3 minutes, allowing for all the students in a typical lab section to take their own data rather than share a single set of data for the entire class.

Procedure Mounting board Materials • Board, pine – 1 pc. 12 in. x 12 in. x 0.75 in. • Wire, copper 10 gauge 15 ft. • Wood tiles (4) 2 in. x 2 in. x 0.25 in. (cut from the 2 in. x 4 in. board) (four one inch flat brackets may be substituted for the wood tiles) • Wood screws (8) 1 in. Manufacturing procedure 1. Set the height of the blade on the table saw to ¼ in. above the table deck. Use the pencil to draw two equally spaced lines along the grain of the wood. 2. Cut a ¼ in. deep groove along each line with the table saw. 3. Measure the insulated wire and use a magic marker to mark it at 10 ft. from one end.

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Tatum, P., & Sundaresan, M., & Pai, D. (2004, June), Monitoring The Health Of Polymer Insulated Electrical Cables Paper presented at 2004 Annual Conference, Salt Lake City, Utah. 10.18260/1-2--12849