One of the first things we may ask for when planning an EV charger installation is 12 months of historical hydro usage. For many homeowners, that can sound like an unusual request. After all, if you already have a 100-amp or 200-amp electrical service, why do we need to know how much electricity you have actually been using?

The reason is simple: before adding a significant new electrical load such as an EV charger, we need to determine whether your existing electrical service has enough available capacity. For homes with a 100-amp service, we need to establish the existing demand on the service before determining how much additional EV charging load can safely be added.

In Ontario, this can generally be done using one of two methods:

- A residential load calculation based on the electrical equipment installed in the home

- The home’s recent historical electrical demand, using utility-supplied data from the most recent 12-month period

ESA specifically recognizes both approaches when determining the available capacity of a dwelling for EV charging.

Even homes with a 200-amp service may require further assessment in some situations.

As a precaution, if a home has several large electrical loads, a heavily populated panel, multiple electrical panels we may also review the home’s historical demand or complete a load calculation. Having a 200-amp service provides considerably more capacity than a 100-amp service, but it does not automatically mean that unlimited additional electrical loads can be added. Our goal is to understand how the home is actually using its electrical service before adding the sustained load of an EV charger.

What Information Are We Actually Asking For?

When we ask for 12 months of hydro data, we are not simply looking at your total electricity bill.

We are interested in your highest electrical demand during the most recent 12-month period.

The most useful information is hourly consumption data showing how much electricity the home used during each one-hour interval.

ESA’s guidance allows historical utility data from the most recent 12 months to be used to establish the dwelling’s existing peak demand.

For example, if your utility data shows that your highest one-hour usage during the year was significantly below the capacity of your electrical service, there may be enough room to add an EV charger without upgrading the service.

That can be very different from simply assuming that every home with a 100-amp service requires a 200-amp upgrade.

Why Hourly Data Matters

Monthly electricity usage does not tell us when that electricity was being used.

Two homes could consume the same amount of electricity over a month but have very different peak demands.

One home might use electricity fairly evenly throughout the day.

Another might have several large electrical loads operating at the same time, such as:

• An electric range
• Clothes dryer
• Electric water heater
• Air conditioning
• Electric heating
• Hot tub
• Pool equipment
• Other large appliances

The electrical service has to be sized for the amount of load that may occur at one time, not simply the total amount of electricity consumed over a month.

That is why hourly historical usage is much more useful than simply looking at the dollar amount on your hydro bill.

How Is Historical Demand Used?

ESA provides a method for determining peak demand from utility-supplied hourly data.

The highest one-hour energy reading from the most recent 12 months is used, and an additional factor is applied to account for possible variation within that hour. ESA’s published example uses 125% of the highest hourly value when determining the estimated peak demand.

The result gives us a much clearer picture of how heavily the existing electrical service has actually been used.

We can then compare that demand against the available capacity of the service and determine how much room may remain for additional loads such as EV charging. For homeowners, the important takeaway is:

We are not guessing how heavily your electrical service is being used. We are using actual historical information from the home whenever possible.

What If I Cannot Get 12 Months of Hydro Data?

That does not necessarily prevent an EV charger from being installed.

If suitable historical demand data is not available, we can perform a traditional residential load calculation using the requirements of Section 8 of the Ontario Electrical Safety Code.

This involves looking at the major electrical loads in the home and calculating the expected demand placed on the service.

Depending on the home, we would collect information about equipment such as:

• Electric heating
• Air conditioning or heat pumps
• Electric range or wall ovens
• Clothes dryers
• Electric water heaters
• Hot tubs
• Pools
• Saunas
• Secondary suites
• Large workshop equipment
• Existing EV chargers
• Other significant electrical loads

We also consider the size and configuration of the home and the rating of the existing electrical service.

The Code applies demand factors because it would be unusual for every electrical appliance in a home to operate at its maximum output at exactly the same time. The calculation allows us to estimate the realistic maximum demand on the service.

Historical Demand vs. a Load Calculation

Neither method is automatically better in every situation.

Historical demand tells us what the home has actually done during the last year.

A traditional load calculation estimates what the home could reasonably demand based on the equipment that is installed.

Historical data can be especially useful when a homeowner has a 100-amp service but relatively modest electrical demand.

For example, a home with:

• Gas heating
• Gas water heating
• Gas cooking
• No hot tub
• No pool
• Relatively few major electrical loads

may have considerable unused capacity even though the main service is only 100 amps.

On the other hand, a highly electrified home may already place much greater demand on the same size service.

That is why we assess the individual home instead of making a recommendation based only on the number printed on the main breaker.

What Happens If There Is Not Enough Capacity?

If the assessment shows that the home does not have enough available electrical capacity for the proposed charger, that does not automatically mean the only option is a 200-amp service upgrade.

Depending on the installation, there may be several options.

Reduce the EV Charger Output

Some EV chargers can be commissioned at a lower output.

A homeowner who does not need maximum charging speed may still be able to comfortably recharge their vehicle overnight while placing less demand on the electrical service.

Install an Energy Management System

An electric vehicle energy management system can monitor the home’s electrical demand and control the EV charger so that the service is not overloaded.

When the home is using less electricity, the charger can operate.

When household demand increases, the system can reduce or interrupt EV charging.

Under the current Ontario Electrical Safety Code, EV energy management systems are specifically recognized as a method of controlling EV charging demand.

Upgrade the Electrical Service

In some homes, a 100-to-200-amp service upgrade is the most practical long-term solution.

This may be especially worthwhile when the homeowner is also planning:

• Additional EVs
• Electric heating
• Heat pumps
• Induction cooking
• Hot tubs
• Pool equipment
• Home additions
• Battery storage
• Other future electrification projects

The goal is to recommend the option that makes sense for both the current EV charger and the future needs of the home.

Why We Ask for This Before We Start the Job

We want to understand the electrical system before recommending equipment or pricing an installation.

If we know the service capacity and existing demand beforehand, we can give the homeowner a much more accurate picture of what the project may involve.

Depending on the result, the installation might require:

• A standard EV branch circuit
• A reduced charging rate
• An energy management system
• Additional electrical work
• A service upgrade

Knowing this early helps avoid surprises once work has already started.

What Should You Send Us?

If you are considering an EV charger, the following information helps us assess the installation:

• A clear picture of your electrical panel
• A picture of the main breaker rating
• The make and model of the EV charger
• Where the vehicle will be parked
• The approximate route between the electrical panel and garage
• 12 months of hourly hydro usage, if available
• Information about any major electrical equipment in the home

With that information, we can usually get a much better understanding of the installation before arriving on site.

EV Charger Installations in York and Durham Region

GO Electrical provides permitted residential EV charger installations throughout York and Durham Region.

We assess the existing electrical service, review historical demand where available and determine whether your home can support the proposed charger.

If the available capacity is limited, we can explain the options, including reduced charging output, load management or a service upgrade.

Send us a picture of your electrical panel and your 12 months of hydro usage, if available, and we can help determine what options may work for your home.