Why a 48 amp charger is a 60 amp circuit
A load that runs for three hours or more without interruption is conventionally treated as continuous, and continuous loads are sized at 125 percent. Car charging is the purest continuous load in a house: plug in at eleven at night, draw the full rated current until the pack is full, no cycling and no diversity. Multiply 48 amps by 1.25 and you get 60, which is the next standard breaker. The same arithmetic run the other way gives the familiar 80 percent statement — a 60 amp breaker carries a 48 amp continuous load, a 50 amp breaker carries 40, a 40 amp breaker carries 32.
The reason is thermal. A breaker is calibrated to hold its rating in a defined test condition, and a real panel with adjacent breakers in a warm garage is not that condition. The 25 percent margin is what keeps a device that is holding its full rating for eight hours from creeping toward its trip curve. It is also why the failure mode of an undersized EV circuit is a nuisance trip at three in the morning rather than an immediate disaster, and why people are tempted to solve it by fitting a larger breaker, which is exactly the wrong direction.
| Charger output | x 1.25 | Standard breaker | kW at 240 V |
|---|---|---|---|
| 16 A | 20 A | 20 A | 3.8 kW |
| 24 A | 30 A | 30 A | 5.8 kW |
| 32 A | 40 A | 40 A | 7.7 kW |
| 40 A | 50 A | 50 A | 9.6 kW |
| 48 A | 60 A | 60 A | 11.5 kW |
| 64 A | 80 A | 80 A | 15.4 kW |
The factor is a field on this page rather than a constant because the definition of continuous and the multiplier attached to it belong to the code edition your jurisdiction has adopted.
Two different currents, two different calculations
This trips people up more than anything else here. Breaker sizing and conductor ampacity use the design current — the 125 percent figure. Voltage drop uses the actual running current, because volts are lost in proportion to the amps that genuinely flow, and the 25 percent margin is a safety allowance rather than current that exists. Calculating drop on the inflated figure gives a pessimistic answer and sometimes an expensively oversized conductor.
Both constraints have to be satisfied and either can govern. On a short run in a garage next to the panel, ampacity decides everything and voltage drop is irrelevant. On a 150 foot run to a detached garage, voltage drop usually calls for a conductor well above what the current alone needs, and the run stops being a wire question and starts being a subpanel question.
Charging speed, honestly
Delivered power is amps times volts. A 48 amp charger at 240 volts delivers 11.5 kW, and at 3.5 miles per kWh that is about 40 miles of range per hour before losses. Real numbers land below that. Onboard chargers run at roughly 88 to 94 percent efficiency, cold batteries take a further hit, and the charge rate tapers near the top of the pack. Plan on the calculated figure being 5 to 15 percent optimistic.
The more useful observation is that most people massively over-buy charging speed. A 32 amp charger at 240 volts adds around 27 miles of range an hour, which is 270 miles overnight. Very few drivers need more than that, and the difference in installed cost between a 32 amp circuit and a 48 amp one is not the charger, it is the conductor, the breaker, and whether the existing service can carry it at all.
The parts of this that are not a calculation
Whether your service can support the circuit is a whole-house load calculation, not a charger question, and it is the step that most often changes the plan. Where the equipment may be mounted, what protection the circuit requires, whether the receptacle route or the hardwired route applies, and how the disconnect is arranged are all governed by the adopted code and by the equipment listing. Several of them differ for a garage, an outdoor wall and a carport.
Electrical work on a building generally needs a permit and an inspection, and many jurisdictions restrict who is allowed to do it at all. An error in this part of a house burns houses down and kills people. This page sizes and estimates. It does not replace the judgement of a licensed electrician, and it gives no instruction for opening equipment or making connections. What this page produces is a set of numbers to hand to an electrician or attach to a permit application, so that the conversation starts from arithmetic instead of from a guess.
Every threshold on this page — fill percentages, volume allowances, ampacity, the continuous-load factor, derating for ambient temperature and for the number of current-carrying conductors — is shown as an input with a common working default. The figure that governs your installation is the one in the code edition your jurisdiction has adopted, with whatever local amendments came with it, as your Authority Having Jurisdiction reads it. Check the defaults before you rely on them.
See also: circuit load calculator for what else is on the panel, subpanel feeder calculator if the run is long enough to justify one, and voltage drop calculator for the run in isolation.
Questions people ask
What breaker does a 48 amp EV charger need?
Sixty amps, on the conventional continuous-load treatment: 48 times 1.25 is 60, which is a standard breaker size. The relationship also runs the other way, and the 80 percent phrasing is the one most people know — a 60 amp breaker is rated to carry 48 amps continuously. What the calculator will not tell you is whether your panel has room for a 60 amp two-pole breaker, whether the bus can take it, and whether the service as a whole can support another 11.5 kW. Those need a load calculation on the actual house.
Should I hardwire the charger or use a plug?
Both routes exist and the trade-offs are real. A plug-in unit on a receptacle can be swapped or taken to a new house, and it is often the route people take when they want the flexibility. Hardwiring generally allows higher current — 48 amp equipment is normally hardwired — and removes the receptacle as a point of failure, which matters because a high-current receptacle cycled daily is a wear item and there have been well-documented overheating problems with cheap ones. The rules on which is permitted where, and what protection each route requires, come from your adopted code edition. Decide it with the electrician doing the installation rather than in advance.
Can I install an EV charger circuit myself?
In most jurisdictions this is permitted work and inspected work, and many restrict who may do it. A 60 amp 240 volt circuit is not a light fitting: an error at the panel end is a fault current measured in thousands of amps, and the failure mode is an arc flash or a fire in a wall. Some jurisdictions allow a homeowner to permit and perform work on their own dwelling and some do not, and the answer depends on your address rather than on your confidence. Find out from your building department what applies before you plan around it. This page produces numbers for a permit application and for a conversation with an electrician; it deliberately gives no procedure.
Do I need a bigger electrical service for an EV charger?
Frequently, and it is the expensive part. A 48 amp charger adds 11.5 kW of continuous load to a house, which on a 100 amp service is often decisive and on a 200 amp service depends on what else is electric. The determination comes from a load calculation on the actual dwelling — square footage, appliances, heating and cooling — not from a rule of thumb. Where the service is genuinely short there are alternatives to upgrading it: charging equipment with adjustable current limits, load-management devices that shed the charger when the range or the dryer runs, and simply choosing a 32 amp unit instead of a 48. All of them are cheaper than a service upgrade, which brings the utility into the project.
How long does it take to charge overnight?
Divide the energy you need by the delivered power. A 48 amp charger at 240 volts delivers 11.5 kW, so adding 40 kWh takes about 3.5 hours at the rated output. Real sessions run longer: onboard chargers lose several percent as heat, cold packs charge more slowly, and the rate tapers as the battery fills. The practical framing is that almost any Level 2 circuit finishes an ordinary daily top-up overnight. A 32 amp circuit adds roughly 270 miles of range in ten hours, which is more than most people drive in three days.