What is the difference between an essential electrical system (EES) and an emergency power supply system (EPSS)?

An Essential Electrical System (EES) and an Emergency Power Supply System (EPSS) are closely related concepts. The Essential Electrical System is the comprehensive electrical infrastructure designed for continuous power in critical areas, while the Emergency Power Supply System is the subset of the EES that directly deals with providing power during emergency situations. EPSS is a crucial component within the broader EES framework.