Receptacle Roundup V: NEMA 14-50

When the standard for dryer plugs was revised in the ’90s, another connector besides NEMA 14-30 emerged: NEMA 14-50 for electric stoves/ranges, replacing NEMA 10-50.  Cooking can reach higher temperatures, so that standard was given more current.  As NEMA 5-20 is more powerful than 5-15, so too is -50 versus -30 (the current rating, in amperes).  Yet, the pinouts look broadly similar, hence the “14” stays.

p104929d

This is it- the most powerful outlet preinstalled in homes, possibly including your kitchen right now.  Bonus: RVs often have refrigerators, ovens, etc., or just a lot of little stuff.  The 14-50 is thus seen in RV parks, giving shore power to the bigger models.  That’s right- this powerful, standard connector is already along our highways, including (especially!) rural roads.  There are over 10,000 RV parks, making them the focus of cross-country EV trips.

14-50 boasts both 240 volts (reducing transmission and charging losses versus 120V) and high current (50A peak, but 40A sustained is more relevant to us).  All told, this is 9.6 kW sustained, or over six times more power than household 5-15 (120V x 12A, or 1.44 kW sustained).  Few electric vehicles can even take this; most top out at 6.6 or even 3.3 kW.  But if yours can, an eight-hour overnight charge for a car (3-5 miles per kWh) means 210-380 miles of driving.  Assuming your pack doesn’t “fill” in just two or three hours, that is.

There is only one plug standard, in anywhere near wide deployment today, that competes with this.  SAE J1772 can technically reach 80A current and over 19 kW.  However, J-units seen so far actually max out at 75A, and most are 30-40A.  This is at the discretion of the installer, and 30-40A already handles 6.6-kW cars.

The only vehicles sold today that can take this 40A/9.6 kW at 240V are the Teslas, and the 2nd-generation Toyota RAV4 EV, which was actually a partnership with Tesla.  All others are 3.3-6.6 kW or less, including my Zero motorcycle.  Needless to say, Tesla encourages its buyers to install 14-50s in their homes if possible.

And yet, the 14-50 is in mass production, so the receptacle itself costs a few bucks.  Installation is within the reach of a skilled homeowner, as long as you have house wiring that can support it.  Like 14-30, one can also get 120V by tapping only one side, instead of the full 240.  Push comes to shove, you can charge via a slower standard overnight, and carry a 14-50 cord for trips.  Heck, if you decide on 14-30 for home charging, you can hack a dual-capable plug that can fit either:
p14z
The neutral (top) blade is the only difference in interfacing.  It doesn’t take a genius to see that prong can be modified to form the dual-unit.  (Though you need to limit devices charging from a 14-30R to its 30A limit, of course.)  Or a 14-50 socket can be modified to also take a 14-30 plug (disconnect all electricity first, of course).  A 14-30 device should already be upward-safe, by not attempting to draw more than 30A, and threatening the receptacle, circuit breaker, or wiring in the wall.  Don’t ask me for more info on the hack, though.  Doing electrical work in the face of fires or electrocution is a burden of responsibility; if you haven’t figure it out already, then maybe it’s not for you.

Wow!  Why isn’t everyone plugging NEMA 14-50 (literally and figuratively)???  Ranges were not meant to be plugged and unplugged daily- ideally, you’re supposed to hook up a large appliance once, and leave it.  Ranges and similar appliances are supposed to be indoor-only- not left in the rain, let alone mating and demating there.  Combined, these factors make such existing standards undesirable for vehicles in general.  And for curbside units in particular, which might attract vandals.  At 240V, arcs and electrocution are more likely.  Thus, the National Electrical Code has no direct plugging into 240V, without an interface box providing several functions.

A determined person, though, can answer all these challenges.  RV parks see these hookups all the time, outside, without trained customers… but without a plague of electrocutions either.  The parks mount their sockets in a weatherized enclosure.  The lid closes naturally, and even when open tends to direct water from, not to, the connections.  The pigtails then hang down through the door gap; rain wants to run down, not up the cords.  Push comes to shove, you can flip the circuit breaker, plug in, and then reactivate the breaker only when clear of the connection.

p104918d

This doesn’t solve the problem of frequent cycling.  But a new 14-50 receptacle is pocket change, and labor is not much (or free, if you can cope).  This is extra effort, certainly.  For an RV park, abuse may go unnoticed, or repairs may go unheeded.  This includes circuit breakers that are worn, and will now fail short of their intended 50 amps.  Due to this, EV trippers have noted a need to try multiple outlets in some RV parks.  But for a home installation, with minimal user skill, one receptacle should last years.  (I’ll assume your home contains very few vandals.)  If even that’s not enough, you can use a plug saver.  A plug saver is basically an adapter, but a 14-50 to 14-50 “adapter.”  Usage wears the plug saver, not the receptacle.  At a certain point, you toss the plug saver, not the unit built in the wall.

Don’t know if a plug saver satisfies the National Electrical Code.  Perhaps a portable GFI unit might, which coincidentally acts as a plug saver while being a safety device.  I do know that many other countries have 240V as standard, and again, don’t see mass electrocutions.  The point of the NEC may also be to prevent drive-offs from ripping wiring out of the wall, and exposing deadly currents.  In this case, however, many EV manufacturers lock out their drivetrains while the vehicle is plugged, or at least charging.  A plug saver will also reduce damage in a drive-off.

Personally, I find the 14-x plugs and cabling large for carrying on the bike.  But that’s also because I can’t draw 30-50 amps anyway, and have no trunk.  Car owners wouldn’t care about throwing another plug in the trunk, particularly one that allows two, faster standards.  If more EV companies build for these high charging currents, expect to see more 14-50 action.

NEMA 14-50 Plus
-Existing standard like NEMA 5-15
-Cheap and widely deployed- may be in your home right now
-Also deployed near highways for travelers, via RV parks
-240V has fewer losses in car charging
-Far more power than 5-15 (over 6x more); more than any other home outlet
-Separate neutral (return) and ground lines for safety
-Can also deliver 120V (“split phase”)
-Endorsed by one automaker, Tesla
-Can be hacked to accept 14-30 (“downward compatible”)

Minus
-240V technically a greater safety risk than 120
-Mostly deployed in kitchens and RV parks, not truly curbside
-RV installs may be degraded or damaged
-Plugs getting large (more an issue on two wheels)
-Direct plugging (wall-to-vehicle) violates Electrical Code
-Faster… but still a bit slow for highway stops

Neutral
-A billion people use 240V every day
-No more (or less) weather- and vandal-proof than 5-15
-Actually more power than most vehicles can accept
-Not ruggedized for use cycles- like 5-15, but unlike J1772
-Installed range/stove base split with old (10-50) standard, requiring adapter

NEMA 14-50 Ground
This is the “big boy”- the most powerful connector already standardized and deployed in the wider public (not industrial sites).  Support on the vehicle side is quite slim, but if yours will take anywhere near this much power, a compatible plug (or at least an adapter) is good to have for major (hour or more) stops.  A dual -30/-50 plug can be even handier, and no more to carry.

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14 thoughts on “Receptacle Roundup V: NEMA 14-50

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  10. I’m an electrician researching a prospective NEMA 14-50 installation curbside for a Tesla customer. Saving $1600 on a 1772 charger does seem like a big advantage, especially when most of them are only 30A. The Tesla 14-50 Universal Mobile Connector is already a ‘plug saver’ since the UMC is a J1772 connector at the vehicle charge port end, with an EVSE/controller in the middle of the cable, and a proprietary connector that accepts modular adapters (plug-savers) at the line end of the cable. The NEMA 14-50 adapter is one of a half-dozen Tesla offers to fit out its UMC.

    For my application, I will be installing a weather-proof while-in-use enclosure for a NEMA 14-50 receptacle, and intend to more-or-less permanently connect the UMC, and padlock the while-in-use cover shut so that vandals cannot steal the UMC, nor hurt themselves by shoving metal into the 240V 40A socket that will be sitting at eye-level for 8-year-olds on the public sidewalk. The J1772 should prevent drive-aways, and the NEMA 14-50 will not undergo cycling since a) the UMC will remain connected always and b) the UMC will connect via Tesla’s modular UMC-to-NEMA-14-50 adapter.

    My one remaining issue is to identify a while-in-use weatherproof cover that accommodates the 70degree angle of Tesla’s UMC. Basically, from what I can tell by pictures, the thing sticks out a bunch, and won’t likely fit under most covers when they are latched down. I could cut the Tesla modular connector off and install my own 90degree NEMA 14-50 cord end, but then the $750 UMC would be locked into this one NEMA 14-50 configuration, preventing the owner benefitting from the flexibility the modular adapters when taking the UMC with them on trips out of town.

    By the way, the RV style utility pedestals from Midwest and Siemens appear well-suited for use as curbside EVSE power supplies like the Tesla UMC — except for the issue of the covers not being quite deep enough to accommodate the 70deg cord angle. Also, I saw mention on one forum that the Tesla cord hangs opposite to what most cables do, so the pre-wired RV power heads would need to be re-assembled with the NEMA 14-50 receptacle ‘upside down’. Can anyone who’s charged a Tesla using UMC at an RV hookup confirm this? If you charge at an RV hookup where the UMC can connect under a latched cover, please snap a photo of the equipment nameplate and post here, or get in touch with me via my website, PhillyLicensedElectrician.com

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