Amperage and Breaker Chart

This is the table the rest of a home charging project hangs off. Pick a charger output on the left and every other decision follows: the breaker, the conductor, whether the unit plugs in or is wired in permanently, the power it delivers, and roughly how much range an hour of charging returns. There is exactly one rule behind all of it, and it is that electric vehicle charging counts as a continuous load, so the branch circuit is rated at 125 percent of the charger's output.

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What breaker does each EV charger size need?

Multiply the charger's continuous output by 1.25 and round up to the next standard breaker size. Residential two-pole sizes run 15, 20, 30, 40, 50, 60, 70, 80, 90 and 100 amps, with nothing between 50 and 60, which is why 48 amps lands on 60 rather than on an exact match. The miles per hour columns use three efficiencies: 2.2 miles per kWh for a large electric truck, 3.0 for a heavier crossover, and 3.9 for an efficient sedan.

One clarification on the top two rows. The power and miles per hour columns are computed at 240 volts throughout so the table stays internally consistent. A 12 amp charger on a genuine 120 volt household outlet is Level 1 and delivers around 1.4 kW, which is roughly four to five miles of range per hour. A 16 amp charger can be either: 1.9 kW on a dedicated 120 volt 20 amp circuit, or 3.8 kW on a 240 volt 6-20 receptacle, which is the cheapest real Level 2 available.

Two things in that table are worth staring at before you shop. The first is the shape of the middle rows. Going from 32 to 40 amps costs one conductor size and buys roughly two kilowatts. Going from 40 to 48 costs a larger breaker, a hardwired termination and often a heavier conductor for the run length, and buys under two kilowatts. On a car with an 11.5 kW onboard charger that last step is worth having. On a car with a 6.6 kW onboard charger it buys precisely nothing, because the car will never draw it.

The second is the connection column. At 40 amps continuous and below you have a choice: a plug-in unit on a matching receptacle, or a hardwired one. Above 40 amps the choice disappears. Receptacle configurations above 50 amps are uncommon in residential supply houses, and manufacturers ship 48 amp units hardwired as a matter of course. That threshold is the single largest fork in a home charging project, and it is discussed at length in hardwired versus plug-in.

How do I read the chart backwards from a breaker I already have?

Plenty of people arrive at this page from the other direction. There is already a 50 amp circuit in the garage from a welder, or a 30 amp dryer circuit that might be shared, and the question is what charger that supports. The arithmetic is the same rule inverted: one divided by 1.25 is 0.8, so a breaker supports a continuous load of 80 percent of its rating.

One warning attaches to that table. An existing circuit supports the charger shown only if the conductor, the receptacle and the terminations are all rated for a continuous load, and only if nothing else shares the circuit. A dryer circuit that already serves a dryer cannot simply also serve a charger. The exception is a listed automatic transfer device that guarantees only one load draws at a time, which is the whole category covered in dryer outlet splitters, and in dedicated circuit requirements.

Why is a charger circuit always a size bigger than the charger?

A continuous load is defined as one that draws its maximum current for three hours or more. Nobody argues about whether overnight EV charging qualifies. A car plugged in at ten at night and unplugged at seven in the morning has pulled full current for nine hours, which is triple the threshold. The code response is to require the branch circuit to be rated at not less than 125 percent of that continuous load, and the same 125 percent appears again in the service load calculation when an EVSE is added to a house.

The reason for the derate is thermal rather than arbitrary. Overcurrent devices are calibrated on a thermal curve, and a breaker carrying a load close to its rating for hours behaves very differently from one carrying the same current for ninety seconds while a motor starts. Running a 48 amp charger on a 50 amp breaker would put the device at 96 percent of its rating continuously, which is both a code violation and a practical nuisance-trip problem: the breaker will eventually open in the middle of the night, and nobody will understand why.

It also explains why the charger itself has no vote. A 48 amp capable unit dialled down to 40 amps is a 40 amp load and needs a 50 amp circuit. Set it back to 48 and it needs 60. The nameplate maximum matters mainly because it is the largest setting somebody could later select, which is why electricians will normally wire for the nameplate rating rather than for the configured setting, and why buying an adjustable unit and a smaller circuit is a legitimate strategy only if you accept that upgrading the circuit later is a separate job.

Which receptacle goes with which row?

For the plug-in rows, the receptacle is a second lookup with its own ceiling. A receptacle rated 50 amps supports 40 amps continuous, exactly the same 80 percent rule, which is why the ubiquitous NEMA 14-50 outlet is always paired with a 40 amp charger and never a 50 amp one.

The full breakdown of what each configuration means, including why the legacy 10-30 has no equipment ground and what that changes, sits on the NEMA plug types chart. The practical shortlist for a home charging project is short: a 14-50 for a new plug-in install, a 6-50 if the run is long and the three-wire saving is worth it, a 14-30 if you are sharing a dryer circuit through a listed device, and a hardwired whip for anything above 40 amps.

Do not economise on the receptacle itself. A builder-grade 50 amp outlet designed for an RV plugged in twice a summer is the component most likely to fail in the entire installation once it sees a 40 amp continuous load eight hours a night. Contact resistance rises as the contacts wear, every watt of it turns into heat at the plug face, and the failure mode is a scorched receptacle rather than a tripped breaker. The Leviton heavy-duty EV receptacle and the Hubbell industrial 14-50R cost several times what a basic flush-mount 14-50R does, and paying that difference is not optional on a daily charging circuit.

Where does this chart stop being true?

Four places, and each one is worth knowing before you hand the table to anybody.

The conductor column assumes a short run

The copper sizes shown are typical for a short residential branch circuit terminating on 75 degree Celsius rated lugs. They are not a design specification. Published ampacity tables give three columns for the same conductor, one for each terminal temperature rating, and the usable figure is governed by the lowest-rated component in the circuit. A 6 AWG copper conductor is good for 75 amps in the 90 degree column, 65 amps at 75 degrees and 55 amps at 60 degrees, so the honest number in a house is 65. Three adjustments push it lower still: ambient temperature above 30 degrees Celsius, more than three current-carrying conductors in one raceway, and the small conductor rule capping 14, 12 and 10 AWG. The complete tables for copper and aluminium are on the wire gauge ampacity chart.

Distance can override the conductor column entirely

Ampacity is a heat question. Voltage drop is a distance question, and on a long run it decides the conductor instead. A 6 AWG copper run carrying 48 amps is thermally comfortable at 150 feet and electrically poor, because the drop has passed the three percent design target and the charger sees reduced voltage for every hour of every session. That three percent figure is a design recommendation rather than a hard code requirement, which is exactly why it vanishes from quotes. Check your own distance in the voltage drop calculator before you buy wire.

The miles per hour columns are estimates, not promises

Range added per hour is charger power multiplied by the car's efficiency, and real efficiency moves with temperature, speed, terrain, tyre choice and how much of the energy the cabin heater takes. A cold winter night can cost a quarter of the figure shown, partly because the pack itself has to be warmed before it will accept full current. Treat the columns as a planning band rather than a guarantee, and size the circuit so the overnight window has slack in it.

The car may not accept the row you picked

The most expensive mistake available here is buying a row the vehicle cannot use. The car contains its own AC to DC converter, the onboard charger, and that component sets a hard ceiling. Most current vehicles cap at 11.5 kW or below. The Nissan Leaf and early Toyota bZ4X are 6.6 kW, so a 48 amp circuit delivers exactly the same speed as a 32 amp one. Only the Ford F-150 Lightning can genuinely use 19.2 kW, and that needs a 100 amp branch circuit which consumes half of a typical 200 amp service on its own. Check your own car against the battery capacity chart first.

How much does each row of the chart cost to install?

The hardware difference between rows is small and the labour difference is not. A new 50 amp circuit with the panel on the same garage wall is roughly half a day of work. The same circuit fished 40 feet through a finished wall can be two or three times that, and the material cost barely moves. A 60 amp hardwired circuit adds a heavier conductor and a permanent termination but no extra fishing, so the step from the 50 amp row to the 60 amp row usually costs a few hundred dollars rather than a multiple.

That is the argument for wiring the larger circuit at install time even if you buy a smaller charger now. The conductor and the breaker are cheap relative to the labour of opening the same wall twice. Price both options against your own run length in the installation cost calculator, and see the whole thing assembled with prices in the hardwired 48 amp buildout.

What the panel has to say about it

A 60 amp branch circuit is a substantial addition to a residential service. On a 200 amp panel it is 30 percent of the nameplate rating, and the practical answer is usually yes, although a load calculation is a defined procedure rather than a running total of breaker sizes. On a 100 amp panel the same circuit is 60 percent of the service, and the answer is frequently no without either reducing the charger output or adding a listed load management device.

Two physical constraints bite before the arithmetic does. A two-pole breaker needs two adjacent full-height spaces, and tandem or half-height breakers cannot serve a 240 volt load, so a panel full of thin breakers may have no usable space at all. The bus itself also has a rating, and some older load centres will not accept a 60 amp branch breaker at any position. Both are ninety-second visual checks for an electrician and both can change the plan. Run the numbers in the panel load calculator before you commit to a row.

The short version

If you want one sentence to carry away: the breaker is the charger output multiplied by 1.25, rounded up to a real size, and the charger is the breaker multiplied by 0.8. Everything else on this page is commentary on where that arithmetic meets a real house. Pick the smallest row that refills your daily miles inside your overnight window, confirm the car can accept it, confirm the panel can carry it, and then spend the money you saved on cable length rather than on amperage.

Common questions

What size breaker does a 40 amp EV charger need?

A 40 amp charger needs a 50 amp two-pole breaker. EV charging is a continuous load, so the branch circuit is rated at 125 percent of the charger output, and 40 multiplied by 1.25 is 50. That combination delivers 9.6 kW at 240 volts and is the most common home installation in the country, because it is also the largest output a NEMA 14-50 receptacle supports.

What size breaker does a 48 amp EV charger need?

A 48 amp charger needs a 60 amp two-pole breaker, because 48 multiplied by 1.25 is 60. It delivers 11.5 kW at 240 volts, which saturates the onboard charger in nearly every electric car currently sold. There is no 55 amp residential breaker, so 48 amps lands on 60 rather than on something between. Units at this output are hardwired rather than plugged in.

Why does the chart show 80 percent instead of the full breaker rating?

Because the 125 percent continuous load rule works in both directions. Sized forward, a continuous load is multiplied by 1.25 to get the breaker. Read backwards, a breaker supports a continuous load of 80 percent of its rating, since 1 divided by 1.25 is 0.8. This is why a 50 amp circuit gives you a 40 amp charger and never a 50 amp one, no matter what the receptacle is stamped.

Does 208 volts change the breaker size?

No. The amperage rules are identical at 208 volts, so a 40 amp charger still needs a 50 amp breaker. What changes is the power delivered, which drops by roughly 13 percent because power is volts multiplied by amps. A 40 amp charger gives 9.6 kW at 240 volts and 8.3 kW at 208 volts. Some multi-family and converted commercial buildings supply 208 volts rather than 240.

Can I fit a larger breaker to charge faster?

No, and it is genuinely dangerous rather than merely non-compliant. A breaker protects the conductor from overheating, not the appliance. Existing conductors do not become capable of carrying more current because the breaker changed; what changes is that the protection they relied on has been removed. Faster charging requires a larger conductor, a larger breaker and a charger rated for the higher output, all three together.

Which row of this chart should most houses choose?

The 48 amp row if the panel has capacity, because 11.5 kW is the ceiling nearly every current car can actually accept, and the 40 amp row if it does not or if the budget is tight. Below that, 32 amps on a 40 amp circuit is fully adequate for any car with a 6.6 or 7.2 kW onboard charger, which includes the Nissan Leaf and early Toyota bZ4X.

Getting your own panel and load numbers ready for an electrician? The EV Home Charging Install Planner is the paid version of these pages: 8 printable worksheets you fill in with your own numbers, plus the full PDF, $29.