Power availability is the cornerstone of critical applications – including Data Centres, hospitals and airports – but to guarantee availability it is vital to design an electrical architecture specifically for optimized performance. In the absence of a single, universal technical standard, it is possible to identify trends in the construction of Single Line Diagrams. Transfer between different power supply sources is a key part of the optimization process – including the protection of an electrical installation using circuit breaker-based Automatic Transfer Switches (ATS). Developing an understanding of the key requirements for continuity of service – combined with an analysis of loads – is the basis for achieving guaranteed power availability. In this document you will find the basics of optimized design execution – including protection and transfer systems – built on the principles of the separation and independence of these functions.