Lightning Current Propagation in Electrical Conduit

• Published in: IEEE transactions on plasma science Vol. 50; no. 1; pp. 132 - 140
• Main Authors: Brooks, William, Lapointe, Micah, Collier, Landon, Mankowski, John, Dickens, James, Hattz, David, Koone, Neil, Neuber, Andreas
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-01-2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Breakdown; Circuits; Conductors; conduit; Electric breakdown; Electrical grounding; Electrical insulation; Electrical raceways; Insulation; Lightning; Lightning strikes; Resistance; Voltage measurement; Waveforms; Wire; Wires
• ISSN: 0093-3813; 1939-9375
• DOI: 10.1109/TPS.2021.3136447

Investigation of lightning strikes to conductors ran through long spans of rigid steel conduit was performed. An overdamped-exponential current waveform with controlled peaks and rise rates was used to inject simulated lightning strikes. The impact of the length of wire, length of conduit, grounding location/s, and load type was investigated. Breakdown of 600 V, 12 AWG, THHN insulated wire (3.23 mm OD, 2 mm conductor diameter) was observed for voltages above 45 kV. The presence of resistive loads (between wire and ground) in excess of 20 <inline-formula> <tex-math notation="LaTeX">\Omega </tex-math></inline-formula> or current rise times in excess of 5 kA/<inline-formula> <tex-math notation="LaTeX">\mu \text{s} </tex-math></inline-formula> were found to consistently produce breakdown between wire and conduit. Practical power circuit elements such as outlets and splices were found to breakdown at voltage levels much below the wire insulation failure threshold.