What is the maximum discharge voltage of a modern lightning arrestor recommended to be in relation to the BIL of the protected equipment?

The maximum discharge voltage of a modern lightning arrestor should indeed be recommended to be less than 20% of the BIL (Basic Insulation Level) of the protected equipment. This is crucial because the lightning arrestor's primary function is to protect sensitive electrical equipment from voltage surges caused by lightning strikes or switching events.

By ensuring that the discharge voltage remains below 20% of the BIL, the lightning arrestor can effectively divert excess voltage away from the protected equipment without allowing a significant surge to reach it. This maintains the integrity of the electrical insulation and helps prevent equipment failure or damage.

The recommendation balances sufficient protection while optimizing the operation of the equipment. While options indicating higher percentages may seem acceptable, they do not align with best practices for ensuring robust protection. Thus, setting the standard at less than 20% creates a safety margin that contributes to extended equipment life and reliability.