Voltage and Amperage

The nominal design voltage for Level 2 charging equipment is 240 volts. But electrical service varies from place to place. It could range down to 220 volts, and some commercial supplies run at 208 volts. Level 2 charging equipment works across this range.

The other key element is the capacity of the circuit supplying those 240 volts. Amperage is the crucial unit printed on your home's circuit breakers, on every fuse you've ever changed, and it's the electrical unit that describes the maximum flow rate a given circuit can supply. All Level 2 EVSEs are built to work at 240 volts, but they are sold in a variety of amperage ratings to suit the needs of different cars.

Common Level 2 output ratings are 16 amps and 30 amps, but there are others in between and ranging all the way up to 80 amps.

Which one should you buy? Electrician and EVSE specialist William Korthof recommends buying an EVSE rated for the most amps your budget will allow. Prices go up in lockstep with amperage increases, though, both for the unit itself and the wiring necessary to support it.

"You may not need it all with your first plug-in car," he says. "But when the time comes to get another one, it may have a more powerful charger and you'll avoid having to buy a new EVSE to take advantage of it."

Korthof recommends a 30-amp EVSE as the minimum. If you are buying a Tesla — or hope to buy one in the future — you'll need at least a 40-amp EVSE to take full advantage of its quicker charging capacity. The 80-amp hot-rod models are only worth considering if your Tesla is equipped with the twin-charger option.

The circuit breakers that must be installed in your home's fuse box to deliver current to the EVSE must be rated 25 percent higher than the rated output of the charging station. A 30-amp (sometimes 32-amp) station needs a 40-amp breaker. A 40-amp station needs a 50-amp breaker. The 80-amp unit must be backed by a 100-amp breaker.

Additionally, the wiring that runs from the circuit breaker to the EVSE also must be properly sized to handle the amperage and the distance from the EVSE to the breaker. That's another reason why it's crucial to hire an electrician to do the installation.