What is the formula for charger wattage?
Charger wattage is amps times volts. For a 32 amp charger on 240 volts that is 7,680 watts, or about 7.7 kilowatts. That figure is the power the charger can draw, and it is what you compare against other big loads in the house.
Wattage helps you see the charger in context. A central AC unit, an electric dryer and a range each draw a good share of your service, and a charger can be as large as any of them. Seeing the numbers side by side makes it clear why the panel needs a real check.
Keep in mind that the charger rarely runs at that number all night. The car tapers its draw as the battery fills. The calculation still uses the full figure, because the panel has to be safe in the worst case, not the average one.
Why is an EV charger treated as a continuous load?
An EV charger is a continuous load because it can run at steady output for three hours or more. The National Electrical Code requires the circuit and breaker to handle that load at one and a quarter times its rated amps, giving a margin for sustained heat.
Short loads, like a toaster, let wires cool between uses. Charging does not. A car can pull near its maximum for hours, and sustained current is what warms terminals and conductors. The rule exists because heat builds slowly and damages things quietly.
This is why a 32 amp charger lands on a 40 amp breaker and a 48 amp charger on a 60 amp breaker. You may hear the rule described as one and a quarter times the load, and it is the reason behind the simple charger and breaker pairings electricians memorize.
How does the load calculation decide if my panel can take it?
The load calculation adds your home's general loads, big appliances and the charger, then compares the total to your service size. If the total fits within the service rating, the charger can be added. If not, you need load management, a subpanel or an upgrade.
The code calculation is not the same as reading your meter. It applies set factors to things like lighting, appliances and AC, and an electrician follows that method so the result holds up at inspection. A quick guess from the sidewalk cannot replace it.
Arizona homes often reach the limit because of AC and sometimes pool equipment. Share what you have when you call, including the age of the panel, and Vortech will check whether your service can take the charger before you buy one.
What can I do if the calculation says no?
If the calculation says your panel cannot take the charger, you can use a load management device, lower the charger's amperage, add a subpanel, or upgrade the panel or service. Each option solves the capacity problem differently, so the numbers guide the choice.
The smallest fix is often turning the charger down. A lower setting draws less and may still cover your daily mileage. A load management device goes a step further by pausing or reducing charging whenever the house is busy with AC and appliances.
If you want full speed or plan on a second EV, a panel upgrade gives room to grow. See our panel upgrade service, and contact us for a written quote so you can compare the options and decide what fits your budget and your plans.
Need an EV Charger Installed?
Vortech installs Level 2 home chargers across Phoenix, Glendale, Peoria, Sun City, Sun City West and Surprise. See EV charger installation or read the full guide on this topic.
More questions: Home EV Charger Installation: 12 Most Asked Questions Answered