This piece was originally published in the May/June 2019 issue of electroindustry.
Andrei Moldoveanu, Technical Director, NEMA
In preparation for the 2011 National Electrical Code®, a group of experts on electrical safety, including several NEMA Members, was asked to propose requirements for a new category of products called electric vehicle supply equipment (EVSE), popularly (and incorrectly) known as EV chargers. The EV industry was new, and there weren’t many safety Standards for the EVSEs. Even though the NEC is a safety installation code, and not a product one, the implementation was a legitimate one.
To be safe, the experts asked that EVSE cables be selected from a number of trusted options already listed in the code. Those codes could offer a guarantee that EV customers handling EVSEs would be protected both from electric shocks and temperature.
As the EV industry progressed, the demand quickly grew for a charging time comparable with filling a traditional car’s fuel tank. That could be accomplished by pumping more electric current at higher voltages. An issue arose when using NEC-recommended cables. In order to keep the cables cool enough to handle, they would have to be built to have such huge diameters that the cables would be impractically heavy and rigid.
One way to solve this is a cable technology that has been used until now only for exotic applications. The technology sounds simple. A hot cable is placed inside another cable that circulates very cold fluids around it to keep the external jacket safely warm. The cable technology needs a pump, sensors to control the temperature and flow, and a heat exchange mechanism to get rid of the heat—all under centralized control. Compared with a regular cable, this cooling cable would cost much more. In fact, it’s no longer a cable—it’s a complicated system.
Given the market interest, UL has drafted an annex on this topic to the UL 2202 Standard that governs dc fast chargers (DCFC). Armed with the assurance that certified DCFCs are protecting the EV user and, after a lot of convincing from NEMA, the 2017 NEC has relaxed its EVSE requirements, allowing for liquid-cooled cable options. Only one “minor” problem remains: the EVs should be capable of handling that much power. ei