The breaker decides the charger, at 80 percent. Enphase's quick install guide for the IQ EV Charger 2 instructs that the maximum charging current be configured to no more than 80 percent of the circuit breaker's rated capacity, and lists the breaker for each model: 50 amps for the NEMA 14-50R version, and 60, 80 or 100 amps for the hardwired versions. Eighty percent of a 60-amp breaker is 48 amps, and 48 amps at 240 volts is 11.5 kilowatts. The condition that changes the answer is the panel: the charger that fits is the one the spare breaker space and the service size allow, not the one with the largest number on the box.
Eighty percent of the breaker, not one hundred
The 80 percent figure is the same rule as the 125 percent one, read from the other end: a continuous load is sized at 125 percent of its current, and 1 divided by 1.25 is 0.8. Both appear in manufacturers' own installation documents because NEC Article 625 treats electric vehicle supply equipment as a continuous load. Emporia's installation guide for its Classic charger puts it in plain words for a plug-in installation: "Per NEC continuous load requirements, a 50A receptacle and breaker are required for this 40A charging application", and it specifies a dedicated two-pole breaker of 50 amps or more for a 40-amp charger and of 60 amps or more for a 48-amp charger.
Example, on Enphase's published breaker table, with output power computed at 240 volts:
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| Breaker | Maximum charging current | Power at 240 V |
|---|---|---|
| 50 A | 40 A | 9.6 kW |
| 60 A | 48 A | 11.5 kW |
| 80 A | 64 A | 15.4 kW |
| 100 A | 80 A | 19.2 kW |
Emporia's guide states 9.6 kW at 240 volts and 40 amps and 8.3 kW at 208 volts and 40 amps for the same current, which is the second half of the arithmetic: 240 times 40 is 9,600 watts, and 208 times 40 is 8,320. Voltage at the panel, not the charger's label, sets the kilowatts, and the same is true of a 30-amp induction cooktop competing for space in the same box. Enphase's guide adds that the charger can be installed on a smaller breaker by limiting the charger's current during commissioning, so the hardware number and the installed number are two different figures.
The standards a manual names
A home charger's compliance is a list, and Enphase prints it for the IQ EV Charger 2: NEC Article 625, SAE J1772, NACS, ENERGY STAR, UL 2594, CSA C22.2 No. 280-22 and a long tail of others. Each entry does a separate job. SAE J1772 is the connector and the signaling between the charger and the car; UL 2594 is the safety standard the equipment is listed to; NEC Article 625 is the installation code the electrician works from; ENERGY STAR is the energy certification.
Emporia's guide cites a specific subsection, 2023 NEC Section 625.17(A)(3)(a)(ii), as the basis for supplying a plug-connected unit with a cable under 6 feet, and warns that because its charger has built-in ground-fault protection, a GFCI breaker on the same circuit can cause unwarranted tripping, recommending the hardwired method where a GFCI breaker is required. Those are the kinds of details that decide an installation, and both of them come from a manufacturer's document rather than a product page.
ENERGY STAR limits what the box burns doing nothing
A charger draws power around the clock. The ENERGY STAR Version 1.2 specification for electric vehicle supply equipment sets ceilings by mode. No Vehicle Mode, which corresponds to SAE J1772 State A and is intended to be the lowest-power mode, is capped at 4 watts plus allowances: 1.0 watt for an in-use Wi-Fi or Ethernet interface with wake capability, 2.0 watts for cellular, plus listed auxiliary allowances such as 1 watt for a speaker and 1.5 watts for occupancy sensing. Idle Mode, which corresponds to State C, is capped at 0.4 times the nameplate maximum output current in amperes, plus 4 watts, plus the same allowances.
Run those two equations on a 48-amp, Wi-Fi-connected unit. Idle Mode is 0.4 times 48, or 19.2 watts, plus 4 watts, plus 1.0 watt, for a ceiling of 24.2 watts. No Vehicle Mode is 4 plus 1.0, or 5.0 watts; sitting at that ceiling for a full year of 8,760 hours would be 43.8 kilowatt-hours. The specification also requires every certified unit to be listed for safety by a Nationally Recognized Testing Laboratory, and covers Level 1, Level 2 and DC-output equipment up to 350 kilowatts. That standby figure is small next to a car's consumption and large next to the packs on an electric bicycle, which is the comparison that tells you where it belongs in a household's electricity bill.
Before you buy a home EV charger
- The breaker rating the manufacturer's installation guide requires for the current you want, at 80 percent of the breaker.
- The panel's spare capacity and voltage, since 240 volts and 208 volts give different kilowatts from the same amps.
- The compliance list in the manual: SAE J1772 or NACS, UL 2594 and NEC Article 625 named individually.
- Whether the unit is plug-connected or hardwired, and what the guide says about GFCI breakers on that circuit.
- The cable length in feet and the mounting position, measured against where the car's inlet sits on the driveway.
- The installed electrician's quote, which is the larger half of the cost for most homes and not part of the charger's price.
- The warranty document and what it excludes for outdoor installation, alongside the network or app subscription, if any, priced per year.