A home or small commercial building does not automatically need a service upgrade just because an EV charger is being added. In many cases, the charger can be installed on the existing service after a proper load calculation. In other cases, a lower charging rate or an approved load-management system can avoid an otherwise unnecessary service upgrade.
The size printed on the main breaker is only one piece of the puzzle.
What Determines Whether the Existing Service Is Large Enough?
An electrician should look at several things before choosing the charger circuit size:
- The building's existing electrical load. Electric heat, heat pumps with auxiliary heat, electric water heaters, ranges, dryers, hot tubs, shop equipment, and other large loads all affect how much capacity remains.
- The service and panel condition. A service may have adequate calculated capacity but still have an old, damaged, crowded, or unsuitable panel. If that is the issue, see our guide on when an electrical panel should be upgraded.
- The charger's actual maximum charging current. A 48-amp charger is a much larger load than a 24- or 32-amp charger. Installing the highest-output charger available is not always necessary.
- Whether load management is available. Some listed EV charging systems can monitor the building's electrical demand and reduce or pause vehicle charging when other loads are high. In the right application, that can allow EV charging without increasing the service size.
Does a 100-Amp Service Automatically Need to Be Upgraded?
No. A 100-amp service may be able to support EV charging, particularly at a lower charging rate or with properly designed load management. The answer depends on the actual load calculation and the rest of the electrical system.
The reverse is also true: a 200-amp service does not automatically mean there is unlimited spare capacity. A heavily electrified home with electric heat, water heating, cooking, laundry, HVAC, and other large loads can use a substantial portion of a 200-amp service.
This is why adding up breaker handle ratings is not a valid substitute for a load calculation. Most branch circuits are never loaded to their breaker rating at the same time.
Why Is the EV Charger Breaker Often Larger Than the Charging Current?
Electric vehicle charging is treated as a continuous load under NEC Article 625. In a typical installation, the circuit is therefore sized above the charger's maximum charging current.
Common examples are:
- 32-amp charging on a 40-amp circuit
- 40-amp charging on a 50-amp circuit
- 48-amp charging on a 60-amp circuit
The exact breaker, conductor size, wiring method, equipment rating, and termination requirements still have to match the charger manufacturer's instructions and the applicable electrical code. Installing a larger breaker without the properly sized conductors can create the same kind of hazard discussed in our article on undersized wiring.
Do I Need the Fastest Level 2 Charger Available?
Not necessarily. The best charging rate depends on the vehicle, daily driving, how long the vehicle normally sits overnight, and how much electrical capacity is available.
For many drivers, a modest Level 2 charging rate is enough to replace a normal day's driving while the vehicle is parked overnight. Choosing a sensible charging rate can reduce installation cost and may eliminate the need for a service upgrade.
A charger should be selected around the actual use case rather than simply choosing the largest amp rating available.
What If the Charger Causes a Breaker to Trip?
Do not solve that problem by simply installing a larger breaker. A breaker that repeatedly trips after an EV charger is installed can indicate an overload, an incorrect charger setting, improper circuit sizing, a loose connection, defective equipment, or another issue that needs to be diagnosed. See why breakers keep tripping for more information.
Will I Need a Permit or Inspection?
Permit and inspection requirements depend on the local authority having jurisdiction and the scope of the work. A proper EV-charger installation should be designed around the electrical code, the equipment listing and instructions, the existing service, and any local permitting requirements rather than treated as a simple appliance hookup.
Bottom Line
Before buying a charger based only on its advertised maximum output, have the existing service evaluated. A load calculation can determine whether the building can support the desired charging rate and whether the best solution is a standard charger circuit, a lower charging rate, load management, a panel replacement, or a full service upgrade.
Request a consultation with State of the Arc Electric if you want the service and panel evaluated before selecting an EV charger.