This SAE Recommended Practice covers the design and application of primary on-board wiring distribution system harnessing for surface vehicles. This document is intended for single phase nominal 120 VAC circuits that provide power to truck sleeper cab hotel loads so that they may operate with the main propulsion engine turned off. The power supply comes from alternative sources such as land-based grid power@ DC-AC inverters and auxiliary power generators. The circuits may also provide power to improve vehicle performance through charging batteries or operating cold-weather starting aids. This document is not intended to provide guidance for electric or hybrid electric vehicle wiring circuits. Refer to SAE J1673 for high voltage automotive wiring assembly design. Engine block heaters are 120 VAC devices that are used on a multitude of vehicle platforms in addition to trucks with sleeper cabs. Generally@ the engine block heater circuit is wired independent of hotel loads. SAE J2698 does not apply to independently wired engine block heater circuits. Engine block heaters that are integrated with hotel loads are subject to the guidelines in this recommended practice. It is understood that drivers may choose to operate 120 VAC devices with the truck moving or at rest. For example@ a passenger may operate the microwave or watch television and need to operate an inverter. The environment that these devices are operated in can also vary with exterior ambient temperature extremes. Exposure to oil and vibration are other elements that typical household 120 VAC wiring would not normally be exposed to; therefore@ the construction of this power distribution is made more robust for a mobile trucking environment. Driver interaction with the 120 VAC power through use of appliances or connection of cord sets requires special attention to safety aspects dictated in regulatory standards from Nationally Recognized Testing Laboratories (NRTLs) approved labs like Underwriter??s Laboratories (UL)@ Canadian Standards Association (CSA) or from the National Electric Code (NEC) that are not common practice with typical 12 VDC vehicle wiring. This recommended practice supports that all electrical materials@ devices@ components@ appliances@ fittings and equipment shall be Listed@ Labeled or Certified to UL and CSA standards and shall be connected in an approved manner when installed. Detailed requirements are listed hereafter.