EV charging reference charts

What are these charts for?

A home charging project is unusual among home improvement jobs in that almost every decision in it is a lookup. How big is the breaker: a lookup. What conductor does that breaker need: a lookup. Does the conductor survive the distance: a lookup with one multiplication. How fast will the car charge: a lookup against the car's onboard limit. What does a full charge cost: a lookup against your state's average rate. There is very little judgement in the numbers themselves. The judgement is in knowing which lookup applies and where each table stops being true.

That is why this section exists separately from the install guides. The guides argue a case. These pages just give you the table, complete, with the derived columns already worked out, plus enough explanation that you can tell when the table has stopped describing your situation. Every chart page names its own limits explicitly, because a reference table quoted outside its assumptions is worse than no table at all.

The one table everything else hangs off

EV charging counts as a continuous load, meaning a load expected to run at its maximum for three hours or more. Overnight charging is the textbook example: a car plugged in at ten at night and unplugged at seven in the morning has drawn full current for nine hours. Continuous loads are sized at 125 percent, so the breaker is always a step above the charger, and the conductor follows the breaker.

The full version of that table, with the 208 volt column, the plug-in versus hardwired threshold and miles added per hour at three efficiencies, is on the amperage and breaker chart. Note that above 40 amps continuous the connection method changes: a NEMA 14-50 receptacle supports 40 amps continuous and no more, and units above that are hardwired.

Charts about your car, not your wall

The single most expensive misunderstanding in home charging is thinking the wall unit sets the speed. It does not. The car contains its own AC to DC converter, the onboard charger, and that component has a hard limit. Feed a car with a 6.6 kW onboard charger from a 48 amp wall unit and it takes 6.6 kW, exactly what a 32 amp unit on a much cheaper circuit would have given it.

Here is that effect in miniature. Watch the rows where the numbers stop climbing between columns: that is the onboard charger saturating, and every dollar spent on circuit capacity beyond that point buys nothing at all.

Miles per hour figures use each car's own efficiency, which is why an efficient sedan gains more range per hour than a truck on the identical circuit. The full grid, including the 3.8 kW and 19.2 kW columns, is on the charging speed chart, and the pack sizes, ports and full-charge times sit on the battery capacity chart.

One honest caveat runs through all three of these charts: capacities and onboard charger ratings vary by trim, model year and options, and usable capacity is always smaller than gross capacity. Confirm against your own window sticker or owner's manual before anybody sizes a circuit around a number you read here.

Charts about money

Three charts, and between them they answer the two questions that decide whether the project is worth doing: what will the install cost, and what will the electricity cost afterwards. The national average residential rate used across this site is 16.5 cents per kWh, and the spread behind that average is enormous. A state at 11 cents and a state at 41 cents are running the same car for wildly different money, and a time-of-use plan moves the number further than the state average does.

The install cost chart is deliberately wide in its ranges, because real quotes are. The variable that moves a bid by hundreds is almost never the hardware. It is the run length, the wall and ceiling access, the panel condition and the local labour rate. On most jobs the labour line is the largest single line on the invoice, which is why shopping harder for a charger saves less than people expect and why getting two written quotes saves more.

The cost per mile chart is the one to send to somebody still deciding between an electric car and a petrol one. It crosses electricity rate against vehicle efficiency and gives cents per mile, with a fuel comparison beside it, and it includes charging losses honestly rather than pretending every kilowatt-hour billed reaches the battery. Run your own numbers in the cost per mile calculator and the installation cost calculator.