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. It requires consideration of voltage levels, environmental conditions, and manufacturing processes, adherence to relevant standards, and optimization through simulation. The CT Trouble function in the B30 and B90 relays detects this condition by using a low-set differential element, typically set around 10% of the least heavily loaded circuit connected to the bus, that asserts after a settable time delay. The CT Trouble alarm can be sent via SCADA to operating. 35 kV switchgear supports sub-transmission and industrial feeders that need higher insulation and fault duty. Proper BIL, clearances, and arc controls ensure safe operation. Voltage/BIL: 35 kV class, typical BIL 170 kV. Short-circuit: 25–40 kA short-time withstand common; confirm with system fault. Line protection concepts, such as overcurrent and distance arrangements, satisfy this requirement, even though short circuits in the busbar zone are cleared after certain time delay. Between live parts of opposite polarity, 251-600V, Through air gap is 1", Over surface is 2".
