This SAE Recommended Practice covers the design and application of a 120 VAC single phase engine based auxiliary power unit or GENSET. This document is intended to provide design direction for the single phase nominal 120 VAC as it interfaces within the truck architecture providing power to truck sleeper cab hotel loads so that they may operate with the main propulsion engine turned off. The purpose of this Recommended Practice is to provide design direction for the single phase nominal 120 VAC APU as it interfaces within the truck architecture providing power to truck sleeper cab user loads, HVAC loads, and vehicle battery charging, so that they may operate with the main propulsion engine turned off: This Recommended Practice applies to factory and after-market installed APU systems providing 120 VAC single phase power as a convenience for operator and passenger use. APUs are intended to power user loads not essential to vehicle operation or safety (e.g., HVAC, TV, microwave ovens, battery chargers for mobile phones or laptop computers, audio equipment, etc.); Systems typically incorporate a diesel engine, a generator, a control system and power distribution wiring. Requirements are given for the performance, safety, reliability, and environmental compatibility of the system; These are recommended guidelines to be used by OEM and APU or GENSET manufacturers in the development of their own specifications, which may incorporate more or less stringent requirements; This Recommended Practice scope excludes military vehicles, bus and 28 V systems.