tentatively believe that an amendment is warranted to facilitate the manufacture of fuel cell and other vehicles. If FMVSS No. 305 were not amended, the electrical isolation for fuel cell stacks would need to be 500 ohms/volt or greater to comply with FMVSS No. 305, which may not be technically feasible. Proposal for Electrical Isolation Option In consideration of the above, NHTSA is proposing to add an option that would permit an AC high voltage source that is connected to a DC high voltage source post-crash to have electrical isolation no less than 100 ohms/volt provided the high voltage source also meets physical barrier protection requirements. Specifically, the electrical isolation option for electrical safety in the proposal requires that the electrical isolation of a high voltage source be greater than or equal to one of the following: (1) 500 ohms/volt for an AC high voltage source; or (2) 100 ohms/volt for an AC high voltage source if it is conductively connected to a DC high voltage source, but only if the AC high voltage source meets the physical barrier protection requirements; or (3) 100 ohms/volt for a DC high voltage source. NHTSA tentatively believes that adding this option into the existing FMVSS No. 305 requirements essentially harmonizes with the electrical isolation option in GTR No. 13. When an AC and DC high voltage source are conductively connected, the electrical isolation measured will be the same for both high voltage sources and approximately equal to the lower electrical isolation measurement of the two. Accordingly, the combined electrical isolation of conductively connected AC and DC high voltage sources can be greater than or equal to 500
tentatively believe that an amendment is warranted to facilitate the manufacture of fuel cell and other vehicles. If FMVSS No. 305 were not amended, the electrical isolation for fuel cell stacks would need to be 500 ohms/volt or greater to comply with FMVSS No. 305, which may not be technically feasible. Proposal for Electrical Isolation Option In consideration of the above, NHTSA is proposing to add an option that would permit an AC high voltage source that is connected to a DC high voltage source post-crash to have electrical isolation no less than 100 ohms/volt provided the high voltage source also meets physical barrier protection requirements. Specifically, the electrical isolation option for electrical safety in the proposal requires that the electrical isolation of a high voltage source be greater than or equal to one of the following: (1) 500 ohms/volt for an AC high voltage source; or (2) 100 ohms/volt for an AC high voltage source if it is conductively connected to a DC high voltage source, but only if the AC high voltage source meets the physical barrier protection requirements; or (3) 100 ohms/volt for a DC high voltage source. NHTSA tentatively believes that adding this option into the existing FMVSS No. 305 requirements essentially harmonizes with the electrical isolation option in GTR No. 13. When an AC and DC high voltage source are conductively connected, the electrical isolation measured will be the same for both high voltage sources and approximately equal to the lower electrical isolation measurement of the two. Accordingly, the combined electrical isolation of conductively connected AC and DC high voltage sources can be greater than or equal to 500
nprm-fmvss-305-03032016.docx