Decarbonisation of electricity sector, potential increase in electricity demand driven by incorporation of segments of heat and transport sectors, and conditional asset replacement drive the desire for cost-effectiveness of the use of existing assets and use of non-network solutions. A Working Group is tasked to review present and, if needed, propose a new security of supply standard. This study reports on the part of work carried within review. It describes drivers and objective for review, used analytical methodology, and relevant drivers. The results of case studies carried out on illustrative high-voltage networks topology show breakeven value of lost load and economically efficient degree of redundancy for different values of drivers. The study concludes with the key findings of the study.