Receptacle Roundup VI: NEMA 6-15 and 6-20

Wait a minute- who messed up a standard 3-prong?


The cross-compatible NEMA 6-20R can accept a 6-15 or 6-20 plug, for currents of 15 amperes or 20A, respectively.  This is exactly how a NEMA 5-20R has a T-shaped slot, for both 5-15P and 5-20P.  NEMA 6 runs at 240 volts, however, not 120V.  To keep people from frying things trying to jam in 5-x plugs, a 6-15P has two horizontal blades.  The 6-20P, then, has one vertical (left), one horizontal.

So the currents are the same between NEMA 5 and 6, but voltage doubles.  Power then doubles, at 2.88 kW, sustained (6-15) or 3.84 kW sustained (6-20).  An electric car, charging overnight (say, 9 hours) would then fill a 23-35 kWh battery pack, for 68-150 miles of range.  Since cars (but not my Zero) prefer 240V, this is a fine standard, as long as it’s common and widespread. So where do we find 6-x outlets?

These sockets are sometimes found in small shops, including home workshops, but the killer app turned out to be… motels, SCORE!  The heater/AC units in the average motel are juuust powerful enough to ditch NEMA 5 for more power, and NEMA 6 worked nicely.  Like a dryer, a dual HVAC unit can draw serious power for heating elements, which merits 240V.  EV enthusiasts have run cords from their rooms; a motorcycle might even be wheeled into a ground-level room.

p104965dYou can recognize a motel likely to have NEMA 6-x by its through-the-wall HVAC units and exposed grills.  Most often, the establishment will be in the classic motel layout, with back-to-back room rows.  If the place looks more like a solid block, it’s more likely to have central air, and you might get a more-interior room away from parking.  Assuming it’s not too crowded, don’t forget to ask for a ground-floor room (unless you have lots of extension cord).

A 6-x can also be installed for home charging; they are already seen occasionally for large power tools and other gear too hefty for NEMA 5-x.  The wiring is similar to other 240V circuits, like NEMA 10-30 dryer or 10-50 stove installations that may be in a house already.

Note that all these applications I’ve mentioned are indoors.  These receptacles are no more weatherproof than the standard 3-prongs they supplement.  In your garage, that’s fine.  For a driveway, you’ll need a rain enclosure.  It can be a plastic stamping, not expensive.

These outlets aren’t ruggedized, either.  Appliances and power tools get plugged and unplugged even less than consumer 5-x gadgets, certainly not every night.  But, just like 5-x, a new receptacle is a few dollars.  Replacing a worn socket is a few minutes for a handy homeowner, or busywork for an electrician.  If even that’s too much work, you can run the power through a connector saver or plug saver.  If the plug saver ever wears out, you toss it, reducing the cycles on the receptacle itself.

You may get a sort of “plug saver” anyway.  Once you have one 6-x plug, you might as well have the capability to use the other one, too. Adapters between -15 and -20 are small; carrying one on the road should be no problem.  If all the ends are chosen well, it can also act as your plug saver at home.

This standard, like the deprecated NEMA 10-x, is split phase and 3-wire.  There’s no true ground; the ground pin is used as the return (neutral) line for the other two.  Not having a ground line is less safe, which was part of the reason the NEMA 10-x standards got replaced with NEMA 14-x.  And yet, in their decades of existence there weren’t mass electrocutions with NEMA 10 or NEMA 6.  You’re expected to take due caution, follow all instructions, and promptly repair or replace any faulty aspects.  Specialty equipment is mostly a risk to people who wouldn’t install it in the first place.

Possibly a bigger issue is the 240 volts carried, and the safety implications.  It’s better for charging electric-car packs, due to reduced losses.  But higher voltages are more likely to arc across gaps, and burn through insulation.  Our National Electrical Code prescribes EVSE boxes for charging, not a direct wall-to-vehicle cable.  And yet again, I have to note decades of prior experience: Countries around the world use 240V power every single day.  It’s voltages near 120 that might be considered weirdo: it’s the standard of North America, Japan, and some other countries.

The biggest strike against NEMA 6-x, though, is that it’s simply unimpressive.  At home, overnight, many EV enthusiasts have plenty of time to charge from regular NEMA 5-15, which is already there.  If 5-15 is too slow, one of the dryer plugs is more likely in the house, and possibly by or in the garage.  If not, 5-20 is often an easy upgrade from 5-15, while not needing extra safety gear.  On the other hand, there are plenty of faster charging standards- starting with dryer plugs, then going way faster.  “Double the standard 3-prong” isn’t saying much.  Thus, there is only mild support for NEMA 6-x in the EV world.  One group is offering J1772-to-NEMA-6-20 adapters, for those without a J1772 connector on their vehicle.  (Mostly homebuilt EV conversions, also motorcycles and scooters.)  But even this workgroup offers 6-20 only after J1772-to-NEMA-14-50, since that oven plug is a closer match to the J.

Still, a 6-x plug (or an adapter for it) is fairly compact, only a bit larger than a NEMA 5-x plug.  As EV travelers are probably carrying several adapters anyway, this one more is a good candidate.

NEMA 6-15 and 6-20 Plus
-Existing standard, like NEMA 5-15
-Cheap to purchase, installs just like existing NEMA 10-30
-Plugs are cross-compatible, via 6-20R’s T-slot
-Already found in some workshops and motels (along highways!)
-240V has fewer losses- preferred for car charging
-Double the power of corresponding NEMA 5-x outlets

-240V technically riskier than 120V NEMA 5-x
-Direct 240V connection from wall violates electrical codes
-No true ground; use of ground line as neutral is less safe
-Good overnight, but not highway stops; slower than NEMA 14-x and most J1772

-A billion people use 240V every day
-No more (or less) weather- and vandal-proof than NEMA 5-x
-Like 5-15, not intended for frequent cycling (unlike J1772)
-SAE J1772 doesn’t have a true ground, either
-Motorcycles and scooters don’t benefit much from 240V versus 120V
-Receptacle may be 6-15, not the cross-compatible 6-20; may require a plug adapter
-Plugs close to standard 5-x in size (more an issue on two wheels)

NEMA 6-15 and 6-20 Ground
These close standards are already in use for large equipment; an EV is another example.  As a home charging solution, it works well in a dry, private garage, overnight.  On the road, a 6-x cord or adapter could be worth bringing for overnight stops, or just in case.


4 thoughts on “Receptacle Roundup VI: NEMA 6-15 and 6-20

  1. Pingback: Receptacle Roundup VII: Miscellaneous NEMA 6 | cableflux

  2. Pingback: The “HospitalEV” Industry | cableflux

  3. Pingback: Receptacle Roundup XIIa: European Level 1 | cableflux

  4. Pingback: Receptacle Roundup XIIb: Japanese Level 1 | cableflux

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