What does the Basic Impule Level (BIL) Rating of an Electrical Equipment Mean?

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Electrical equipment, including wires and cables, are designed to withstand short-term, but very high-voltage pulses such as those sometimes caused by lightning and switching surges. These “spikes,” as they are sometimes called, typically have a rise time in the range of 1.5 microseconds and a fall time around 40 microseconds.

BIL of Electrical Equipment
BIL means
Basic Impulse Level. The basic impulse level (BIL) is the maximum impulse voltage that electrical equipment can withstand without damage. For a cable or wire, it is the maximum impulse voltage that the wire or cable is designed to withstand without damage. Common BIL ratings are for different voltage systems are shown below:

System Voltage Rating (KV) Basic Impulse Level (KV)

2.5

60

5.0

75

8.0

95

15.0

110

25.0
150

35.0

200

69.0

350
138.0
650