The NEC requires a minimum spacing of 12 inches (305 mm) between busbars, but this can be reduced based on the busbar current and configuration. Engineers frequently rely on a busbar insulator size chart to determine suitable dimensions, voltage ratings, and mechanical strength before installation. Choosing correctly affects electrical clearance, heat dissipation, and structural stability in switchboards, panels, and substations. This. A manufacturer of electrical automation panels is not required to use a certified busbar system or to subject it to short-circuit tests, provided that it complies with Table G3. 1 where it breaks the distances down depending on bus configuration (edge. Introduction: The National Electric Code (NEC) and other regulatory bodies have established guidelines for busbar clearances and spacings to ensure safe operation and prevent electrical shock. Multiple sizes, threads and creepage distances are available to simplify panel layout and ensure safe clearances.