USA DOT Issues Final Rule that Modifies FMVSS 305 - Electric Powered Vehicles.

On June 14, 2010, the National Highway Traffic Safety Administration (NHTSA) published a Final Rule (FR) to amend FMVSS 305 in response to a petition for rulemaking from the Alliance of Automobile Manufacturers (AAM). [Vol.75, Number 113; Docket No. NHTSA-2010-0021]. NHTSA is issuing this Final Rule to facilitate the development and introduction of fuel cell vehicles, a type of electric-powered vehicle, and the next generation of hybrid and battery electric powered vehicles. It does so by revising the agency's standard regulating electrolyte spillage and electrical shock protection for electric-powered vehicles to align it more closely with the April 2005 version of the Society of Automotive Engineers (SAE) Recommended Practice for Electric and Hybrid Electric Vehicle Battery Systems Crash Integrity Testing (SAE J1766).

The standard currently requires manufacturers to design their vehicles so that, in the event of a crash, a vehicle's propulsion battery system will be electrically isolated from the vehicle's electricity-conducting structure. As amended, this rule provides greater flexibility, requiring manufacturers to design their electrically powered vehicles so that, in the event of a crash, the electrical energy storage, conversion, and traction systems are either electrically isolated from the vehicle's chassis or their voltage is below specified levels considered safe from electric shock hazards. As requested by the petitioners, this FR specifies the following electrical isolation requirements: 500 ohms/volt for AC and DC high voltage sources and 100 ohms/volt for DC high voltage sources with continuous monitoring of electrical isolation.

On October 9, 2007, NHTSA published the Notice of Proposed Rulemaking (NPRM) to upgrade FMVSS No. 305, mostly in line with the revised SAE J1766.1.

The highlights of the NPRM:

• Distinguishing between electrical isolation values for DC and AC currents based on relative risk of harm to accommodate fuel cell vehicles and setting the value for DC high voltage systems at 125 ohms/volt.
• Broadening the requirement in S5.3 from 'electrical isolation' alone to 'electrical safety', and permit achieving compliance either through electrical isolation or through a low voltage option under which the post-crash voltage of the source must be less than or equal to 60 volts of direct current (VDC) or 30 volts of alternating current (VAC).
• Adding a definition for 'high voltage source,' and applying electrical safety requirements to any high voltage source, instead of to only the propulsion battery.
• Harmonizing the rear moving barrier impact test conditions of S6.2 and S7.4 of FMVSS No. 305 with the revised FMVSS No. 301.

The following points highlight the key differences between the requirements of the FR and the proposed requirements in the NPRM:

• S5.3 has been revised to require 100 ohms/volt electrical isolation for DC systems with continuous monitoring of electrical isolation during vehicle operation, rather than the more conservative value of 125 ohms/volt proposed in the NPRM, based on new analysis of available data.
• S5.3 has been revised to include an explicit low voltage option for providing electrical safety. A new paragraph, S7.7, has been added that details a procedure for voltage measurement to determine if the voltage source is of low voltage.
• A new paragraph, S5.4, has been added to specify requirements for vehicles equipped with electrical isolation monitoring systems. A new paragraph, S8, has been added that details a test procedure to confirm the functioning of the isolation monitoring system.
• S3 and S4 now clarify that 'working voltage' is used (as opposed to actual voltage only) to identify a vehicle as subject to FMVSS No. 305 and to identify a source as 'high voltage.'
• S7.6.6 and S7.6.7 are modified to specify that the electrical isolation of a high voltage source in ohms/volt is obtained by dividing the electrical isolation resistance of the high voltage source by its working voltage.
• Some definitions of terms used in FMVSS No. 305 have been added or altered for greater clarity.
• Minor editorial corrections have been made to other parts of the regulatory text and to Figures 1 through 5.

NHTSA responded to Hyundai's request for interpretation of S5.2 in this FR because the NPRM had already proposed to modify the language in S5.2. NHTSA concurs that battery modules located outside the occupant compartment should be treated in the same manner as those located inside the occupant compartment, provided that they remain attached to their anchorages. Technical changes to the proposed text in S5.2 have been made accordingly.