Yes, there can be a significant difference between using "Aluminum in Metallic Raceway" and "Aluminum in Nonmetallic Raceway" in fault current calculations for ACSR overhead cable.ACSR (Aluminum Conductor Steel Reinforced) overhead cables are typically installed in metallic raceways, such as conduits or cable trays. The metallic raceway provides a low-impedance path for fault currents, which can result in higher fault currents at the transformer secondary compared to using aluminum in nonmetallic raceways.The reason why POCO's calculator does not include an option for ACSR is likely because the calculator is designed for use with underground cables, which are typically installed in nonmetallic raceways.MH's calculator includes "Aluminum in Nonmetallic Raceway" option, which is more appropriate for underground ACSR cables. However, using this option for overhead ACSR cables may result in underestimating the fault current, especially for short-circuit conditions.The difference between using AL in metallic vs. nonmetallic can be a couple of hundred amps, as you have observed. This difference can be significant, especially for larger transformer sizes and longer cable runs.To ensure accurate fault current calculations for overhead ACSR cables, it is recommended to use a calculator that specifically includes an option for ACSR in metallic raceways. This will provide more accurate results and ensure proper protection of electrical equipment. Flag for review