Here's a paper from California that shows the development of EVSE safety requirements:
2.2 Safety is Foremost
Safety was and is the primary reason charging equipment and safety standards have progressed in the direction they have. Related to this is the issue of liability.
Some EV enthusiasts assert that existing plugs and receptacles, such as NEMA 14-50R or -30R, provide sufficient safety for an EV application. As far as we know, this claim is unsubstantiated by any independent testing. While RVs, clothes dryers, welders and so on use these receptacles, the duty cycle of these do not compare to that of EVs. With EVs, regular connection and disconnection of the vehicle to the charging equipment happens twice a day at a minimum (e.g., when leaving home in the morning and when returning in the evening). When public or workplace charging is used, this number is more.
Clothes dryers and welders on the other hand are typically plugged in when installed and are not unplugged until removed (e.g., once or twice over a span of years). Even portable welders are not moved with great daily frequencies. RVs on average are only temporarily used (e.g., during vacation periods each year). As such, they do not get plugged in and unplugged daily throughout the year.
California wants 35,000 EVs operating in California by 2003. This would equate to 25.6 million connections/disconnections per year. Potential for an accident to occur where someone inadvertently touches an energized plug that is partially inserted into a receptacle is greatly increased. Therefore, the connection method for EVs to the off-board equipment must be fool proof.
I found a briefing paper from BC, Canada that covers EV charging infrastructure. They compare/contrast US NEC and Canada Electric Code (CEC) requirements. They say that NEC is more restrictive than CEC.
http://www.bchydro.com/etc/medialib/int ... -Aug09.pdf
It's dated July 2009 so it should be quoting the 2008 (current) US NEC.
The info they list for L1 specifies exactly which types of plugs and outlets are necessary. The info for L2 and L3 simply show 'grid' connection. Then there's this from page 56:
Power Requirement: Dedicated branch circuit with NEMA 5-15R or 5-20R Receptacle.
Power Requirement: Dedicated branch circuit hardwired to a permanently mounted
EVSE with the following specifications:
240VAC/Single Phase, 4-wire (2 Hot, GND, Neutral), 40Amp Breaker
Section 625.13 Electric Vehicle Supply Equipment.
Electric vehicle supply equipment rated at 125 volts, single phase, 15 or
20 amperes or part of a system identified and listed as suitable for the
purpose and meeting the requirements of 625.18, 625.19, and 625.29
shall be permitted to be cord-and-plug-connected. All other electric
vehicle supply equipment shall be permanently connected and fastened
This section has three phrases - L1, other approved systems that also meet other sections, and hard-wired. The green section is where we're getting hung-up - look - it says plug!
BUT - only if identified and listed as suitable for the purpose AND meeting requirements of these three other sections
. Let's look at these...
Section 625.14 Rating:
Level 1. 125vac. This method, which allows broad access to charge an
EV, permits plugging into a common, grounded 125-volt electrical
receptacle (NEMA 5-15R or 5-20R) when cord-and-plug is approved.
Level 2. 240 VAC, 40 amp. electric vehicle supply equipment shall be
permanently connected and fastened in place.
NEC 625-14 is the limiting phrase. This is what forces commercial suppliers of approved L2 EVSE to ship them without a plug and requires that electricians hard-wire the devices when installing them, and will be used by the home insurance company to approve or deny a claim if the device burns the garage down.