Receptacle Roundup II: SAE J1772

Now here we go- a connector actually designed for vehicle charging, and since then endorsed by carmakers.  So let’s have a look:
This power standard (“SAE J1772 2009”) was de jure ratified by the Society of Automotive Engineers, based on previous pin-and-sleeve industrial connectors.  It was then adopted by every carmaker that can, has been deployed by the thousands, and become the de facto standard for “Level 2” charging.  (The European version is electrically the same, but uses a slightly different connector based on European options.)  The existence of a standard and their presence in the field plants a flag in a way that 5-15s and 5-20s do not.  Each one says “Here’s your charging- specially designed.  You won’t get stranded.”

So how’s this Level 2 a step above Level 1?  First, the power: J1772 is based on 240 volts, the maximum available in homes, small offices, and most storefronts.  As I mentioned in the previous Roundup, cars operate their electric drives at high voltage, to reduce gear shifting.  Direct drive (one speed) requires a few hundred volts, well above the 120V from standard outlets.  While a charger can upconvert voltages, we’d rather not, and upconverting from 240V still beats 120.  (My Zero motorcycle operates at 67V– motorcycles weigh so much less than cars that shifting is less necessary.  So I don’t care either way.)

J1772 also handles higher currents.  The latest specification goes up to 80 amperes, which would clearly whip the household 3-prong.  Of course, manufacturers are free to implement their own designs, as long as they meet the overall spec.  Since most onboard vehicle chargers can’t take more than about 30 amps anyway, many J-units (including most public deployments) top out at 30-40A, which then includes a bit of “future proofing.”  A few run up to 75A, while some cheapos might not break 20A.

Overall, higher voltage and current mean 3 to 7 kilowatts delivered in most designs, with the really good installs at 18 kW.  Blam- charging falls from overnight (or longer) to half or less.  Toss in the lower conversion and resistance losses from the higher voltage, and standard wall outlets at 1.44 kW look kinda lame.  Partial or even full recharges other than at home or work are now appealing, instead of merely doable.  Still, if all you want is 120V, the J-standard lets a connector tap just one side and split the 240.  Because you never know.

Second, the safety aspect: J1772 can be plugged in with wet hands… during a storm, while standing in a puddle.  A frequent catchphrase is ‘you can lick it.’  What, now?  The specification requires that the connectors be ‘dead’- no juice is flowing until after the hookup is successful.  And a successful mate can neither be held nor licked.

Notice in the picture that there’s little visible metal- plenty of plastic (black), but hardly any accessible electrical contacts (yellow brass).  Not only are the actual sockets shrouded in nonconductive resins, but then there’s that outer sleeve.  (The vehicle end is similar- each pin is surrounded by a sleeve, plus an overall shroud.)  Your fingers can’t bridge from contact to contact, since all that sleeving on each side closes up before the metal will mate.

After that, there’s a passive electrical safety feature.  The ground wires are “first to make, last to break.”  The bottom (ground) contacts are longest, and will hook up before the power pins (top).  Thus, even if the power pins were shorted by water or (somehow) your fingers, electricity might still prefer the metal ground path.  This is true at almost any time in the mating process.

Even after that, there are active safety features.  The two small pins are for electrical signals, not power.  They’re “last to make, first to break.”  A J1772 connection will not go live and send power until the signal pins tell it to do so, a “handshake.”  Not only are all the sleeves closed up, but with enough lag, you may have already let go of the handle.  How does the signaling work?  One pin indicates proximity- a simple “I’m here and hooked up” flag.  This proximity signal gets cut by the hardware latch, which must be open to physically mate or demate.  The other pin not only acts as proximity, but tells the vehicle how much current this J-plug can handle.  The vehicle side will not go live, and power will not truly flow, until these signals are read successfully.  You may then hear a click, as a relay closes and allows power flow.  (This handshake also tells the vehicle not to pull away while plugged, though it’s left to the vehicle manufacturer to implement a drive lockout.)  Then, on unplugging, the opposite happens: handshake signals drop and the power goes dead, before the shrouds can give finger access.

Feel safe yet?  Maybe a little too safe?

Third, J1772 was inherently designed for outdoor deployments and thousands of cycles, unlike many other standards.  In particular, your dryer was never intended to be plugged and unplugged daily, or more.  Supposedly, you can drive over the J-handle, though I’ve never tested this.  If you’re on the street, you have to expect street wanks.

So what’s not to like?  More power and more safety, with accessory features and more lifetime?  Have you guessed ‘more cost’?  The connector alone costs about $200, and that’s a dead component- no power hookups, relay, or handshaking circuits, let alone integration labor.  We’ve been told that costs will fall as J-systems ramp up in volume.  But it’s been three years (almost a generation in electronics and the Internet), and there are about ten thousand of these things running, counting home and public units but not Europe.  Still $200 at this writing, possibly $170 in bulk quantities and cruddy Chinese tolerances.  Meanwhile the NEMA receptacles are a few bucks at any home supplier, even the high-powered sockets.  I can’t even find the J-connector at my area big-box stores, and had to order away.

Overall, it’s like overkill.  People weren’t dropping left and right from the old connectors; an SAE J1772 2013 spec could lose one or more safety features, and still keep its safety record.  Really, were people licking power plugs?  And so what if you wear out one of those other connectors?  At even $160 for a J, you’d have to ruin conventional sockets multiple times over before reaching cost parity.

Even the weatherproofing issue is a bit of a dodge.  RV parks and marinas have let people plug in for decades, without even a sunshade.  RV pedestals simply mount receptacles in a rain enclosure, often facing down, with a water-shedding door.  You’d want to check the socket condition first, shake off your hand and plug lightly, and preferably not stand in an actual puddle.  But that’s simply due care, and recommended anyway even with J1772.  In either case, GFI already exists, though it’s best not to rely on a single defense.

I don’t actually believe automakers specified J1772 to hold up electric cars.  But I don’t consider this spec and its current implementations to be a slam dunk, either.  Third-party builders are already working on it…

SAE J1772 Plus

-Higher voltage, much higher power than NEMA 5-15… multiple times more

-Still allows 120V circuit if necessary

-Safe and shockproof… way shockproof

-Weather- and vandal-resistant

-Deployed widely, both shore and vehicle sides, in many markets

-Clearly signals EV support to bystanders


Way more expensive than competitors, even at comparable powers… multiple times more

-Not back- or cross-compatible with alternatives, without serious equipment

-Multi-hour recharging still not fast enough in some cases (though that’s partly the vehicles’ fault)


-Different systems offer widely different currents and charge speeds

-High voltage and power not strictly necessary by many vehicles and situations

-Weather- and vandal-proofing nice but not necessary in your garage

SAE J1772 Ground

Already widely deployed in public, so de facto standard.  Better deal with it if you want to charge on trips.  In your own garage, though, there are plenty of cheaper options, including lower and slightly-higher power levels.  As ‘Level 2’ implies, this is not intended for ultra-cheap Level 1, or even-faster Level 3.


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