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LIGHTNING ISOLATION TRANSFORMERS (LITs) are used for signal transformer applications with signal levels up to 400 V peak to peak. LITs are transformers, with or without an internal-winding screen, with a rated impulse withstand voltage greater than the peak voltage of the expected common-mode surge environment. LITs are applicable to component for surge protection against indirect and direct effect of lightning or other transient overvoltage. LITs are used to mitigate the onward propagation of common mode voltage surges. This standard defines test circuits and test methods for determining and verifying the LIT surge parameters. Preferred performance values for key parameters are given. This standard doesn't cover LIT operation under differential mode lightning surge conditions.