Receptacle Roundup IV: NEMA 10-30 and 14-30

I said in the last Roundup that TT-30 was too similar to dryer outlets.  Dryer sockets which offer more power, and are also widely installed already.  Accidentally forcing in a TT-30 plug can then fry your equipment.  Hmmm, widely installed and lots of power… why not recharge EVs with the dryer sockets instead?

The US had the NEMA 10-30 standard (left) for electric dryers, then went to 14-30.  A part of that was the resemblance to TT-30.  But mostly, 10-30 (sometimes listed as “3-prong”) saved metal during World War II shortages.  Instead of a neutral line, the two live lines dump their power to the ground line.  Not using a neutral saves copper; several yards, at a hefty gauge, in most homes being built, was a whole lotta copper.  NEMA 14-30 (“4-prong”) restored a neutral, and is in homes built after about 1996, or old homes that retrofitted.p1479

Both of these dryer receptacles are 240V, which I don’t need but cars like.  It’s split-phase 240, so you can get 120V if you want.  Just like the power company’s service to a house, two live AC wires are used, in mirror-image phases.  The ground is defined as being halfway between AC phases.  Thus, using either live will yield 120V relative to the ground.  But when using both lives, they act as +120V and -120V relative to each other.  This was done so dryers could run heaters at the more-efficient 240V, while still using standard, cheap 120V lights and controls.  Electric vehicles can use 240V directly, to reduce losses, or tap 120V as that’s plenty of voltage in my case.

These dryer receptacles, now on 240V, deliver 30 amperes of current.  That’s 7.2 kilowatts of electricity, peak load, or 24 amps/~5.8 kW sustained load after a 20% safety margin.  What does that mean for EV owners?  That’s a few times more power than the standard NEMA 5-15.  That 5.8 kW, times three to five miles per kWh for average electric cars, means an overnight charge of eight hours could give 130-235 miles of travel the next day- or, more driving than you actually do, I would guess.  However, that range is a bit moot, as few cars have batteries of 46 kWh or more… and few have chargers that can take 5.8-7.2 kW.  That’s right- we are now looking at a plug that has too much power for many electric vehicles (including mine).

Drivers of experimental EV conversions had typically liked the dryer plugs.  Aside from 240V, it yields more than enough juice to work with, while being available in many basement or garage workshops.  Now, factory electric cars often come with 3.3kW chargers, drawing ~14A from this connector.  At 3.3kW (including some losses and overhead), a fully-depleted Toyota Prius Plug-In recharges its ~4 kWh battery pack in an hour and a half.  Charging tapers off towards the end, to prevent overcharging.  The larger Chevrolet Volt pack charges in just a few hours, not overnight.  The large Nissan Volt pack charges completely in not quite eight hours.

EVs on sale with faster onboard chargers include the Ford Focus EV, with a similar pack size to the 2011-12 Leaf.  But the Focus’ 6.6 kW throughput will fully charge in half the time.  All Tesla-based cars have even more powerful chargers, going up to an optional 20 kW for some Tesla Model S builds.  The Toyota/Tesla RAV4 EV has a 10 kW charger, for its hefty pack.  Finally, the 2013 Leaf itself now goes to a 6.6 kW charger, at least for the trim levels above the base model.  The base Leaf S still does 3.3 kW.

A dryer outlet then adds plenty of range for plenty of people… but overnight, or at least over a few hours.  This is still not something you’d do at a highway rest stop.  Meanwhile, almost all these existing receptacle installations are in private homes, or possibly laundromats and hotels.  (Yes, I’ve heard of people getting permission to run a cord to a commercial laundry room.)  Very few are installed curbside.  So far as I’ve heard, none of these receptacles are installed for workplace charging.  That’s the next place after your own home where you would logically use a charging outlet.

Neither 10-30 nor 14-30 are weatherized, vandal-resistant, and ruggedized.  In fact, dryer plugs were designed for the exact opposite- indoor, private installations with practically no use cycles.  How often do you move your dryer around, if ever?  No, only the J1772 connectors were expressly built for use and abuse.  And yet, abuse is a solvable problem- a weather enclosure is still cheaper than what a J-unit costs, even if you have to replace the receptacle several times due to wear.  EV experimenters using these plugs did not churn through outlet after outlet.

240V outlets, when used directly for vehicle charging, actually violate the National Electrical Code where 120V wouldn’t.  240V is inherently riskier than 120; you’re more likely to spark or arc at higher voltages.  Unplugging a high-voltage connection while under load will cause a nice, blue-hot flash, which is part of the wear issue.  The NEC wants you to use some sort of deliberate EVSE, like a J1772 box.  Aside from electrical safety and wear lifetime, J1772 can also disable the drivetrain, preventing the socket from getting ripped out of the wall.

Again, these are solvable problems.  European, Asian, African, and some Latin nations have distributed 240V power (including to untrained users) for decades now, without mass casualties or burnt-up sockets.  And even in North America, RV parks exist by the thousands.  They have plugged and unplugged untrained enthusiasts at 240V for decades- outdoors!- without being considered unsafe, and without drive lockout.  (For that matter, gas hoses don’t have lockout.)

Of course, foreign plugs were designed for 240V all along, and don’t do the split-phase trick.  Without splitting phase, these foreign interfaces maintain a separate ground and neutral, like our 3-prong connectors.  When ground and neutral are combined, you don’t really have a ground to act as a safety wire, as it’s carrying current.  Lots of current.  The 14-30 then, with its extra prong and separate lines, gives shocks and other excess current somewhere to go other than through you, or any sensitive electronics.

Speaking of extra prongs- the 14-30 was designed to somewhat resemble another connector, the 14-50.  Used for electric ranges, the 14-50 has even higher power; 50A peak (12 kW), 40A sustained (9.6 kW).  The difference is that the 14-50 has a straight-blade neutral, instead of the 14-30’s visibly L-shaped prong.  This is what prevents accidental mating.  For vehicle use, owners have either cut down their neutral prongs, or cut a notch in the 14-50R neutral slot, to allow cross-compatibility.  (Drawing 30A from a 50A outlet is perfectly safe; it’s 50A from a 30 that’s bad.)  Of course, no commercial entity would sell you this hack.  Aside from violating accepted, industrywide standards, it’s a physical and fiduciary liability.  But once a plug is in private hands…

NEMA 14-30 Plus
-Already standardized and grandfathered in, like NEMA 5-15

-Cheap and deployed across North America- may already be in your house

-Higher voltage better for car charging

-Higher power than 5-15 (by up to 4 times) or even TT-30 (up to 2x)

-Can also yield 120V, together with 240V or separately (“split phase”)

-Neutral (return line) and ground separate, for additional safety

-Can be hacked into upward compatibility with NEMA 14-50

Minus
-Found in laundry rooms- not deployed in public places, by any reasonable criterion

-240 volts technically a bigger safety risk than 120V

-Direct plugging (receptacle to vehicle) at 240V violates electrical codes

-Charges still measured in hours, still too slow for road trips

-Plugs physically large (more an issue on two wheels)

Neutral
-A billion people use 240V every day without electrocution or fires

-Actually exceeds usable power levels of many EV chargers today

-No accommodation for outdoor use/frequent cycling, like 5-15 but not J1772

-Installed dryer base split with 10-30, requiring adapter or hack

NEMA 14-30 Ground

The new 14-30 dryer connector is widely deployed in homes, and is very rarely seen on the street from EV supporters.  It may actually be too much power for your vehicle charger.  And yet, it’s not enough power for highway stops.  A 14-30 cord is handy to have, especially as it can be hacked into a 14-50 cord.

NEMA 10-30 Plus
-Already standardized and grandfathered in, like NEMA 5-15

-Cheap and deployed across North America- may already be in your house

-Higher voltage better for car charging

-Higher power than 5-15 (by up to 4 times) or even TT-30 (up to 2x)

-Can also yield 120V, together with 240V or separately (“split phase”)

Minus
-Old, deprecated standard

-Looks like TT-30, which can be forced into 10-30 receptacle

-In laundry rooms- not deployed in public places, by any reasonable criterion

-240V technically a bigger safety risk than 120V

-No true ground technically a safety risk

-Direct plugging (receptacle to vehicle) at 240V violates electrical codes

-Actually exceeds usable power levels of many EV chargers today

-Charges still measured in hours, still too slow for road trips

-Plugs physically large (more an issue on two wheels)

Neutral
-A billion people use 240V every day without electrocution or fires

-Actually exceeds usable power levels of many EV chargers today

-No accommodation for outdoor use/frequent cycling, like 5-15 but not J1772

-J1772 combines ground and neutral, too

-Installed dryer base split with 14-30, requiring adapter or hack

NEMA 10-30 Ground

Superseded by 14-30, the question of 10-30 installation is now moot.  However, if you have an existing 10-30 receptacle near the garage, it will still spank a NEMA 5-15 with the additional cord.

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7 thoughts on “Receptacle Roundup IV: NEMA 10-30 and 14-30

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