NACS, CCS1 and J1772: which EV adapter you actually need

Four connectors, and what each one carries

There are only two kinds of current going into an electric car, and every connector argument is really about which one.

AC comes from a wall — a household outlet, a Level 2 box in a garage, a destination charger at a hotel. The car converts it to DC internally with its onboard charger, and that onboard charger is the ceiling. A 7.7 kW onboard charger will draw 7.7 kW from a 19 kW wall unit and no more.

DC comes from a fast charger that does the conversion itself and pushes DC straight into the pack. This is what people mean by fast charging, and it is measured in tens or hundreds of kilowatts.

• J1772 is the AC connector every non-Tesla electric car in North America has used. AC only, five pins.
• CCS1 is J1772 with two large DC pins added below it. The top half is the same J1772 plug, which is why a CCS1 car can take a J1772 AC cable directly with no adapter at all.
• NACS, standardised as SAE J3400, is the connector Tesla designed and most manufacturers have now adopted. It is smaller than either, and it carries both AC and DC on the same two power pins.
• CHAdeMO appears on the Nissan Leaf and little else in North America. It is DC only and it is being retired.

Which adapter you need, by which way round you are going

Adapters are directional. The name usually describes the plug the adapter accepts, then the inlet it presents — but not every seller writes it the same way round, so read the picture, not the title.

J1772 to NACS (AC). For a car with a NACS inlet using a J1772 AC charger. Small, inexpensive, and the one Tesla has historically shipped with the vehicle. AC only.

NACS to J1772 (AC). For a car with a J1772 inlet using a NACS AC source — a Tesla Wall Connector in a garage, or a destination charger at a hotel. AC only. This is the one most non-Tesla owners actually want, and it is the one most often confused with the DC adapter below.

CCS1 to NACS (DC). For a car with a NACS inlet fast charging at a CCS1 station. Needs the vehicle to support CCS on its hardware — early Model S and Model X need a retrofit, and no adapter substitutes for that.

NACS to CCS1 (DC). For a car with a CCS1 inlet fast charging at a Supercharger. This is the expensive one, because it has to carry hundreds of amps of DC and handshake with the station. It only works where the network has opened the site to other vehicles and where your car is on the supported list.

What an adapter cannot do

This is the part the listings do not say.

1. 1It cannot change AC into DC. An AC adapter at a DC station will either not latch or will fail the handshake. Nothing bad happens; nothing good happens either.
2. 2It cannot raise the current the car will accept. If the vehicle's onboard charger is 7.7 kW, that is what you get from any AC source.
3. 3It cannot make an unsupported car charge on a network that has not enabled it. The handshake is software, and the adapter is not part of it.
4. 4It cannot make a damaged inlet work. If the pins are discoloured or the plastic is deformed, the inlet is the repair, and an adapter over the top of it concentrates the same heat in a smaller place.

The current rating is the number to check

Every adapter has a rated amperage, and it is the only specification that matters for safety. A 40 A adapter on a 48 A circuit will run hot, and heat in a connector is cumulative — it degrades the contact, which raises the resistance, which makes more heat.

Check the rating against the *circuit*, not against what you usually draw. A 48 A wall unit dialled down to 32 A today is still a 48 A wall unit tomorrow, and the setting is in software.

Fitting and using one without damaging the inlet

• Support the adapter's weight. Let it hang on the cable, not on the car's inlet.
• Push it fully home before the cable goes in. A partially seated adapter makes a small contact patch carry full current.
• Do not stack adapters. Two adapters in series double the number of contact resistances and nobody has tested the combination.
• Keep the contacts dry and clean, and do not lubricate them. Contact grease on a high-current pin is a fire, not a fix.
• Store it out of the footwell. It is a hard object and it belongs in the boot.

What to buy

For AC use around town, the direction you need is decided entirely by which inlet your car has. Nothing else about the car matters, and a well-made AC adapter is not an expensive part.

For DC, the adapter has to be rated for the current the car will pull and it has to be on the network's supported list. This is the one to buy from a manufacturer that publishes both, and the one where the cheapest listing on a marketplace is the wrong economy.