March 13, 2024

The Importance of an EV Charger Load Calculation


9 Min. Read

This article was originally published January 31, 2023 and was updated March 13, 2024.

Studies have shown that electric vehicle (EV) drivers find at-home charging to be the most convenient, cost-effective option—particularly when a Level 2 EV charging station is available. Installing a powerful Level 2 EV charger at your residence allows you to completely refuel your electric car’s battery range overnight rather than relying on the small range you can accumulate with the less-powerful charging cord that came with the vehicle.

Being able to charge your vehicle overnight at home ensures that it’s ready for your travels the next day and eliminates the need to stop on your errands or commute while you wait for a public charger to become available. Charging the EV battery at home when utility prices are generally lower also saves money, making overnight EV charging a more cost-effective charging solution.

Installing a Level 2 charging station, however, is more complex than purchasing one and plugging it in. Even if you already have a 240-volt outlet for your electrical dryer. Your home’s electrical system might need upgrading to support the electrical load required for a Level 2 EV charging station.

About EV Charger Load Calculations

A key to successful Level 2 charging installation is calculating household and EV charger load and ensuring you have enough power to safely charge your EV.

If not done correctly, the likelihood of EV charging station failures, damage to your home’s electrical system or EV, and even injury increases exponentially. Repairing damages from improper electrical work can be costly and time-consuming, so doing it right the first time is important.

Doing a household and EV charger load calculation is complicated and requires expert training in electrical work and EV charger safety requirements. For the safest, best result, you must get an accurate assessment of your home’s electrical capacity and EV charger load calculations in accommodating new charging equipment.

Electricity Basics: Volts, Amps, Watts

Electricity is similar to water in the sense that it flows through a conductor from the source to the terminal device. In the case of water, a hose or pipe is typically the conductor. With electricity, the electrons flow through wires made out of material such as copper or aluminum.

The speed of water flowing through a hose or pipe is measured in gallons per minute, while pressure in the hose or pipe is measured in pounds per square inch (PSI). The speed of electrons flowing through a wire is measured by volts (V) for electricity, and the pressure, or force, is measured with amperes (A or amps).

Consumption of electricity by a given device (watts) is measured by multiplying amps by volts, or W=(A*V). For example, a refrigerator uses 300 to 800 watts, or 3 to 6 amps, and approximately 120 volts. A standard Level 2 EV charging station typically adds about 7,200 watts or 30 amps. The actual electrical load can vary based on EV models and chargers as well as usage.

Related: How Many Amps Are Required For  Level 2 Charging?

Because electrons travel farther and faster at higher voltage, utilities transmit electricity to your home at extremely high voltage. Before it reaches your home, however, the electricity is reduced to a lower voltage by an external transformer and then connected to your home’s electrical panel.

Can My Home Handle a Level 2 EV Charger?

What is the function of a household electrical panel? Your electrical panel is crucial in preventing a power overload and essentially allocates how much and where electricity is sent in your home.

Traditional electrical panels are shallow metal enclosures that house a collection of circuit breaker switches. Each circuit has a load capacity measured in amps, is connected to incoming high-voltage electricity from the utility, and has a circuit breaker. When the power to the circuit exceeds its load capacity, the circuit breaker trips and essentially cuts the power off.

Electrical panels come in various capacities. Newer homes commonly have panels that accommodate 200 amps or more. Conversely, panels in older homes were not designed for the abundance of electrical appliances currently found in most homes. Their capacity is typically 60 to 100 amps. (The oldest panels have fuses rather than circuits.)

A standard 100 amp panel typically supports 20 circuits and circuit breakers, but a 240-volt circuit requires a double-pole breaker, which takes up more physical space in the panel. Multiple 240-volt circuits for the clothes dryer or an electric range can rapidly max out a panel’s capacity.

How many breakers can a 100-amp panel accommodate? The National Electric Code (NEC) specifies that a panel that size can accommodate up to 42 breakers, but that doesn’t mean they can operate at full capacity around the clock. A professional electrician can use the electrical load calculation of your home to determine the right size for your electrical panel.

By performing a load calculation to determine how much electricity your home is currently using and how much you will need for your EV charger, a licensed electrician can evaluate the current size of your electrical panel to ensure it will be sufficient to safely install and charge your EV.

Smart panels are more sophisticated electrical panels that enable homeowners to manage loads remotely, assess energy efficiency and usage, and have greater control over your energy consumption—making your home more energy efficient. You can program smart electrical panels to turn specific circuits off and on based on optimum usage times for your needs and peak/off-peak load times. You can use smartphone or laptop apps to control your electricity usage in real time. Many smart panels even feature alarm functions that alert you when the electrical system or an appliance malfunctions.

Household Capacity and EV Charger Load Calculations

Determining the total electricity consumption in the house, the electrical panel capacity, and other details to prepare for an EV charging station and other electrification improvements calls for a comprehensive review and load calculation.

A residential Level 2 charging station usually increases a home’s load by around 7,200 watts (7.2 kilowatts) or 30 amps. The actual load will vary depending on the EV model, charging equipment, and hours in use.

Unless you’ve recently had a load calculation or otherwise assessed your electrical panel, you probably do not know what percentage of your household’s electrical capacity is currently being used. Adding the amperage demanded by a new Level 2 charger could overload your circuits. This is why household load calculations are critical before installing an EV charger or other large electric appliance in your home.

How Can I Accurately Assess My Home’s Electrical Load?

Calculating your home’s total electrical demand can be complex, involving understanding the wattage of your appliances and converting them to amperes. Besides major power users like central air conditioning or a clothes dryer, you need to factor in power used by your lighting, small appliances, microwave, refrigerator, dishwasher, garbage disposal, and other electricity-dependent household items.

Worksheets that estimate a dwelling’s load are available online, but they may not give you a complete picture of your usage. If you add a new high-powered electric appliance such an EV charger without sufficient power availability, the result can be disastrous.

Going into the electric panel to assess and measure circuit loads is not a do-it-yourself project. Estimating your electrical load requires experience and knowledge and hiring a licensed electrician with the necessary training and skills to do the calculations accurately and efficiently and safely install your Level 2 EV charger is the best way to protect your family.

AI Load Measurement Innovations

Qmerit, North America’s national leader in installing EV chargers, has developed proprietary artificial intelligence (AI) solutions to streamline the evaluation of panel capacity and overall household load. The Panel Insights tool leverages AI algorithms to evaluate an electrical panel’s specifications and looks at available circuit spaces, tandem breakers, total capacity, and more. Once this has been determined, the LoadCRE (Load Capacity Recommendation Engine) uses those results to evaluate if there is enough breaker panel capacity available to add an EV charging station, electrical water heater or heat pump, or other electrification household improvements.

What are the Electrical Requirements for Installing a Level 2 EV Charging Station?

Once you know your residential electrical capacity, you must also determine an estimated EV charger load calculation. Different brands and models of Level 2 charging stations have different electric power requirements. While installing a Level 2 EV charging station will require a dedicated 240-volt circuit with an outlet or hardwired connection, the EV charger you purchase may use from 32 to 80 amps, depending on the manufacturer. As noted, an older, 60-amp electrical panel is usually too small to handle this additional charging load. A 200-amp panel is ideal, but a 100-amp panel may be sufficient based on the load calculation.

As mentioned, when considering a Level 2 charger, you will need to determine whether your current electric panel can handle the additional load that Level 2 EV charging will require. If not, your electrician will recommend a panel upgrade or a load-shedding solution, whichever best suits your usage requirements. One example of a load-shedding solution is a load controller. These devices attach to selected circuits in the panel and trip the breaker when the current exceeds pre-set limits.

Smart panels are a more sophisticated and expensive solution to manage loads. If you’re considering adding other electrification technologies such as battery storage as well, a smart panel is worth considering.

Most importantly, you must determine if the home has enough overall capacity for the new Level 2 EV charger to function safely and correctly. Your electrician should always sign off on this before you install an EV charger. Otherwise, you risk system failure or even fire damage to your home due to an overload situation. On top of that, the cost of correcting and redoing the work may be substantial.

Getting Expert Help for EV Charger Load Calculation

If you have decided to install at-home EV charging equipment, you must conduct the EV charger load calculation before planning your charger installation.

To do it right and get the best and safest result, reach out for expert help. This is not a DIY project. Many technologies are new or evolving, and you want an electrical contractor who is fully engaged in electrical panel installation and thinking ahead of the curve.

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Author: Greg Sowder

Greg Sowder

President, Qmerit Network