There is no better time than the present to discuss the merits of alternative fuel sources. As the price of gasoline exceeds $2.00 per gallon in many parts of the country the thought of electric vehicles is much more enticing. Add to this the effort that many major automobile manufacturers have put into developing practical electric vehicles and the concept appears to be one whose time has come.
With all that said, the basic concern becomes the proper installation of recharging systems for these vehicles. The installation of these systems is covered by Article 625 and is the responsibility of code making panel 12 (CMP-12). The concern of both the installer and the inspector can be divided into two areas: the installation of the charging system, and the installation of coordinated ventilation systems, when such ventilation systems are required. The scope of Article 625 defines this by stating that “The provisions of this article cover the electrical conductors and equipment external to an electric vehicle that connect an electric vehicle to a supply of electricity by conductive or inductive means, and the installation of equipment and devices related to electric vehicle charging.”
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Recharging Systems
Section 625-2 establishes definitions for certain items that are specific to electric vehicles and the requirements set forth in Article 625. These terms should be reviewed, as many of them may become familiar words in the near future. The definitions of the “electric vehicle connector” and “electric vehicle supply equipment” help in establishing a line of demarcation between what portion of the electric vehicle system is covered by the NEC and what is not. “Personnel protection system” could easily be considered the most important definition that is found in Article 625. This is obviously a primary concern of both the installation and inspection communities as the public may be very susceptible to electric shock when attempting to connect a vehicle to the source of supply, especially if the vehicle is contaminated with items such as rain, snow, road salts or other potentially conductive materials. During the proposal stage of the 1999 NEC, Mr. David Brown submitted a substantial rewrite of Section 625-2. Panel 12 accepted most of the submittal with the exception of tables and criteria for the proper construction and operation of these protection systems. The panel correctly referred these criteria to listing agencies, and they can be found in UL 2231, the Standard for Personnel Protection Systems for Electric Vehicle Supply Circuits.
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Electric vehicle charging systems are manufactured for a variety of voltages and phases and are required to be listed or labeled. Equipment that is rated at 125-volts, single phase and 15- and 20-amperes, or that is part of a system identified and listed as suitable for the purpose, is allowed to be cord- and plug-connected, provided such equipment is in compliance with the requirements set forth in Sections 625-18, 625-19, and 625-29. Any electric vehicle supply equipment that does not meet all of these criteria must be connected with a permanent wiring method and must be fastened in place.
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Sections 625-18 and 625-19 contain requirements for an automatic interlock whereby the electric vehicle connector is automatically de-energized when it is not plugged into the coupler, and strain detection that would automatically de-energize the cable conductors whenever strain that approaches the value required to rupture or separate the cable is reached. These de-energizing requirements are not mandated for the cord- and plug-connected equipment that was described above. Section 625-19 would mandate this cord- and plug-connected equipment be used only for indoor locations.
Overcurrent Protection
Overcurrent protection for and feeders or branch circuits that are used to supply electric vehicle charging systems are required to be sized for continuous duty and rated at not less than 125 percent of the maximum load rating of this equipment. A disconnecting means is also required for equipment that is rated more than 60 amperes or that operates at more than 150-volts to ground. This disconnecting means must be installed in a readily accessible location and be capable of being locked in the open position. A very important safety requirement is a monitoring or transfer system whereby there can be no backfeed from the batteries through the charging equipment to the normal source of power upon the loss of energy from the normal source of power.
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Ventilation
It is important to review the requirement for ventilation where electric vehicle charging equipment is installed and used. One of the more useful changes that transpired in the 1999 NEC was the requirement for tagging by the manufacturer as to whether or not the system being utilized requires ventilation. This is based upon the type of battery that is being used within the vehicle and whether or not gases are produced during the charging of the batteries. If the system is labeled requiring ventilation then the requirements of Section 625-29(d) must be complied with. This requires both intake and exhaust equipment to be utilized for the ventilation system, and electrical interlock is mandated whereby the ventilation system remains energized during the entire electric vehicle charging cycle. Cord- and plug-connected equipment that is used indoors must be supplied by receptacle outlets that are controlled by a switch, and this switch must also energize the ventilation system. Table 625-29(d) is listed in Section 625-29. This table lists the minimum cubic feet per minute that are required and formulas for calculating the minimum cfm for values that are not included in the table. Both the table and the formulas are based upon the operating voltage and current of the charging system. Ventilation can also be accomplished with the total building ventilation system, provided the system has been calculated to do so by a person qualified to perform such calculations.
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During the code making process, various manufacturers of this equipment have been very involved with the development of these requirements. This has been extremely helpful as they have the technical data and support staff necessary to properly address these issues. These installations have a three-fold effect on both the installer and the inspector: the proper installation of the charging equipment, the proper installation of the ventilation systems when required, and the possible change in the size of service or feeder to the premises when the additional loads mandate a sizing upgrade of the service or feeder conductors and equipment. As the technology continues to improve, these systems will become more commonplace and the installer and inspector must be ready to understand and address this technology.
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Photos courtesy of Tom Bilz, Cleveland Electric, and Steve Lawrence, Georgia Power Company. Special thanks to Ron Purvis, Georgia Power, for collecting the photos.
