This document defines the construction, safety, and performance requirements of modular or factory-matched hydrogen gas generation appliances, herein referred to as hydrogen generators, using electrochemical reactions to electrolyse water to produce hydrogen. This document is applicable to hydrogen generators that use the following types of ion transport medium: — group of aqueous bases; — group of aqueous acids; — solid polymeric materials with acidic function group additions, such as acid proton exchange membrane (PEM); — solid polymeric materials with basic function group additions, such as anion exchange membrane (AEM). This document is applicable to hydrogen generators intended for industrial and commercial uses, and indoor and outdoor residential use in sheltered areas, such as car-ports, garages, utility rooms and similar areas of a residence. Hydrogen generators that can also be used to generate electricity, such as reversible fuel cells, are excluded from the scope of this document. Residential hydrogen generators that also supply oxygen as a product are excluded from the scope of this document.