Don’t be Shocked, But EV Charging is Very Safe
By Kevin Miller
December saw the first consumer deliveries of the Nissan Leaf and Chevrolet Volt in the US, and Cobo Hall in Detroit was literally overrun with plug-in vehicles earlier this month for NAIAS. While the vehicles will primarily be charged at home (especially by early adopters of the vehicles), much public money is being invested in building a public, pay-per-use charging infrastructure. While the charging apparatus for use in a vehicle owner’s garage must be designed with user safety in mind, such equipment for use by the general public must be even more so.
With the Volt and Leaf now on the road, and additional manufacturers preparing to launch electric and plug-in-hybrid vehicles, many companies are designing charging and supply equipment for the vehicles. Some of the equipment being designed is for use by vehicle owners in their own garages, and some is being designed for public use, whether for free use from utilities, or pay-per-use by private companies setting up their own network of charging locations. As required by the National Electric Code in the US, virtually all electrical equipment must be certified for electrical safety by an OSHA-accredited Nationally Recognized Testing Laboratory. This requirement includes stuff like cord-connected appliances in your home, the espresso machine at your local coffee shop, and even EV charging stations.
Imagine the following scenario. In rainy Portland, Oregon, a Leaf driver unplugs her Nissan from the overnight charger in her garage and heads out on a rainy morning to drop her children off at the Montessori school, stops by her favorite Fair Trade coffee shop, then heads over the the neighborhood natural-foods store to pick up some locally grown, organic vegetables for the evening’s vegan dinner. Spying the EV-only parking spots near the front of the store, she wheels her car across the sodden parking lot in the rain. Stepping out of her Leaf, she is dismayed to find her Birkenstock immersed in a deep puddle. Grabbing her latte in one hand she heads to the front of the car to plug in the SAE J1772 standard vehicle connector from the store’s public charger. As she stands in a puddle in the rain, plugs in her car, and initiates charging while wiping a wet lock of hair from her face, she doesn’t give a thought to the dangers of using this high-powered electrical device outdoors.
Fortunately, somebody else has. Over the course of the past several years, electrical safety standards have been developed for electric vehicle supply equipment and chargers. In the US, applicable national standards include UL Subject 2594 (Outine of Investigation for Electric Vehicle Supply Equipment) and UL 2202 (Electric Vehicle Charging System Equipment); in Canada, there is a clause dedicated to Electric Vehicle Chargers in standard CSA C22.2 No. 107.1 (General Use Power Supplies). Those standards are used in accordance with the National Electrical Code in the US, and the Canadian Electrical Code in Canada. EV supply equipment that has has been tested by an OSHA-accredited Nationally Recognized Testing Laboratory (NRTL) to the above standards will bear a certification or Listing Mark to show it meets the standards.
Electric vehicle charging systems come in three different power levels,, commonly referred to as Level 1, Level 2, and Level 3. Levels 1 and 2 are defined in standard SAE J1772 (the vehicle connector specification). Level 1 supply is the term for connecting the vehicle to a 120 VAC, 15 A or 20 A branch circuit (which typically gives a full charge in 10-12 hours). Level 2 supply is from a 220-240 VAC, 30 A circuit, which is the same type of electrical circuit employed by a household electrical clothes dryer; this gives a full charge in about 4-6 hours.
Level 3 supply (called DC Fast Charge) denotes a higher charging voltage or current, though it isn’t actually defined in SAE J1772. Nissan’s Level 3 charging, which is an option in the higher trim level Leaf SL, has a maximum voltage of 500 VDC, maximum current 125 A DC, with maximum power 50 kW and uses a charging protocol known as CHAdeMO (Charge de Move), which is a Level 3 protocol (and proposed standard) shared with the Mitsubishi i-MiEV, Peugeot iON, Subaru Plug-In Stella, and the Swiss EV Protoscar LAMPO2.
You may notice there is a subtle terminology difference between supply equipment and charging equipment. Supply equipment gives AC (alternating current) power to a vehicle, which in turn uses its own on-board charging equipment to recharge the batteries. Charging equipment is the circuitry that turns AC power into DC voltage to recharge the batteries; both the Nissan Leaf and Chevrolet Volt have onboard chargers, for use with Level 1 or Level 2 supply equipment. Note that the Leaf can be ordered with a factory-optional Level 3 charging input which provides a DC input to more quickly recharge its batteries from a dedicated power source.
Both Levels 1 and 2 charging use the industry standard SAE J1772 EV connector. The SAE J1772 connector is designed with a grounding conductor, two current-carrying conductors, and two smaller communication pins. The CHAdeMO charging protocol for Level 3 charging employs a custom connector (rather than the J1772 connector) to handle up to 200 A charging current and also facilitate communication between the has developed a connector with power pins, four analog signal pins, two CAN digital signal pins and one ground pin which are implemented so that the control signals can be transferred properly between the vehicle and the charger, to ensure proper grounding prior to energizing the charging circuit.
Whether using a Level 1, Level 2, or Level 3 charger, circuitry in the supply equipment as well as in the vehicle’s onboard charger won’t allow charging to commence if proper grounding of the vehicle to the charging circuit is not present. This ground-proving circuitry is the system’s first line of defense against the possibility of providing and electric shock in the event of a fault. The second line of defense is a Charge Circuit Interrupting Device, or CCID.
Each of the safety standards above specifies one or more mandatory CCIDs, depending on the power level of the equipment. The CCID may be a ground-fault protective device (similar to what is employed on outdoor receptacles), differential current sensors, or similar technology. The CCIDs for use in Electric Vehicle chargers/supply equipment have their own set of standards in the US, UL 2231-1 and 2231-2. Although these standards have similar test requirements to devices such as household GFCI devices, the test specifications differ somewhat, likely because of the fact that GFCI devices are typically installed in or adjacent to a structure, whereas vehicle supply/charging equipment can be installed outdoors in public locations such as curbside or in parking lots. In this case, use of a Listed GFCI device does not exempt the manufacturer of the charging equipment from any testing in UL 2231-2.
With all of the testing specified by the above standards, getting an EV charger to market is not easy. Testing takes a long time and can be onerous. The standards were written as so many electrical safety standards are, to keep users who lack a working understanding of electricity safe while using the electrical equipment. The theoretical Leaf driver above, standing in sandals in a puddle of water while she plugs in her electric car, is unlikely to consider her safety in regards to charging her car. This is why safety standards must address that risk.
When you see your first installed piece of EV supply equipment installed curbside in the near future, if you notice the certification mark of a NRTL, you can consider that it has been rigorously tested for electrical safety. Although standing in a puddle while wearing sandals to connect your electric vehicle for a charge isn’t recommended, the charge equipment has been designed to eliminate the risk of shock in such situations. Owners and drivers of EVs should have no need to worry about their safety, because safety standards and thorough testing have done the worrying – and addressed the issues – for them.