Requirements for 120 VAC Electrical Distribution on Medium and Heavy Duty Trucks

Electrical wiring systems connected to land-based 120 VAC electrical service outlets (shore power) for distribution in medium and heavy-duty trucks are currently being installed by OEM's, dealers and owner-operators to varying standards. A sample system is shown in Figure 1. SAE J1673 covers the design and application of on-board wiring distribution system harnesses on road vehicles for circuits operating between 50 and 600 VDC and VAC. The SAE standard does not specifically cover 120 VAC circuits connected to an electrical service outlet. Parallel to SAE, there are electrical industry standards such as the National Electric Code (NEC) and Canadian Electric Code (CEC) which dictate installation and inspection rules for 120 VAC distribution in structures, marine applications, recreational vehicles and other miscellaneous items but not installations specific to medium and heavy-duty trucks. Further to NEC and CEC there are regulatory standards from Underwriter's Laboratory (UL) and Canadian Standards Association (CSA) which set out rules for 120 VAC power supply cords, extension cords, interconnecting plug and receptacle configurations, etc. CSA also has specific detailed standards for other service connected 120 VAC systems for recreational vehicles and engine block heaters. There are also standards created by specific industries using 120 VAC, such as the recreational vehicle industry, which has codes set out by the Recreational Vehicle Industry Association (RVIA). The Federal Motor Carrier Safety Administration heavy truck inspection/standards group has stated that there are no FMCSA (DOT) standards that apply to this application.

Like the RV industry, it is important that the trucking industry proceed with developing electrical standards that will best support the industry's interests for now and in the future. The need for an all-encompassing recommended practice for nominal 120 VAC wiring on medium and heavy-duty trucks, which includes reference to electric industry and regulatory requirements, is apparent. A system of regulatory approved components is introduced to simplify the installation and electrical standard requirements that the OEM, dealer, fleet, and owner operator must deal with in order to properly install service connected 120VAC systems on their trucks.