NEMA Twist Lock on Single-phase UPS: Determining Pluggable Type A or B Connectors

There are various UPS plug types e.g., Pluggable Type A, Pluggable Type B, or permanently connected equipment. Standards provide guidance for the right usage of plug to make single-phase UPS Pluggable Type A or B. However, due to many overlapping standards, incorrect interpretations, misinformation, and lack of easy-to-understand documentation, there is much confusion about plug/socket types. The confusion multiplies when there no established standard or documentation on how to categorize NEMA twisted plug which is widely regarded as Pluggable Type B. This application note describes how the NEMA twisted plug/socket is categorized as Pluggable Type B through standard interpretation and design practices, can mitigate risk posed by plug-in single-phase UPS, and how end users can ensure that the single-phase UPS they use follows these standards and design practices.