The choice of conductor size from mechanical view point depends on the : External Loading: Wind speed, ice loading and ambient temperature Internal Characteristics: Stranding, modulus of electricity, thermal expansion of the creep. Underground wire sizing is very different from indoor runs, as underground circuits tend to run much longer, which makes voltage drop a major concern. Operating voltage, required number of phases (three-phase or single-phase) and required reliability dictate topology and configuration of the network. Electric power. The NEC (National Electrical Code) provides guidance on how to size wires correctly for feeders and subpanels. This guide focuses on NEC 2023 standards. The wires connecting the main panel to the subpanel are called feeder conductors, and their correct sizing. FWIW, if the transformer is delta delta or single phase 2 wire, the primary fuse being 125% within the full load primary current rating means the secondary conductors are considered protected and may travel any distance without requiring OCPD at the secondary voltage panel board. Copyright © 2008 by the Institute of Electrical and Electronics Engineers, Inc.
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