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A 100-amp home isn't automatically disqualified
Think of your electrical service as a fixed amount of capacity shared by everything running in the house. A new EV charger adds a substantial load, but not every home starts from the same point.
One Sarnia homeowner may use gas heating, a gas range and modest electrical loads. Another may have electric heat, air conditioning, a hot tub and a future basement suite. Those homes need different assessments even if both panels say 100 A.
The key question: how much electrical capacity is available after the home’s existing loads are considered?
Level 1 versus Level 2 charging
| Level 1 | Level 2 | |
|---|---|---|
| Typical supply | Standard household receptacle | Dedicated 240V circuit/equipment |
| Charging experience | Slower; can suit short daily driving | Faster; often preferred for regular home charging |
| New electrical work | Depends on existing circuit and condition | Usually requires a dedicated installation |
| Best decision factor | Daily driving and time parked | Load capacity, vehicle and budget |
Do not select a charger only by its advertised maximum current. The vehicle, available service capacity and installation need to work together.
Three routes an electrician may recommend
Option A: Install a charger within existing capacity
If the electrical assessment supports it, a compatible charging unit can be installed without replacing the entire service. Sometimes a lower charging setting is enough for overnight needs.
Option B: Use suitable energy management
Approved energy-management equipment can limit or adjust EV charging to keep the home within its electrical capacity. Suitability depends on the system, code requirements and equipment configuration.
This is worth investigating before spending thousands upgrading a service solely to add a charger.
Option C: Upgrade the service
If the calculated load is too high or the home has other planned electrical additions, a service upgrade may be the sensible long-term choice.
Read our Ontario panel upgrade cost guide for what changes that quote.
What an EV charger assessment should include
- Panel and service rating. The number on a breaker isn't the entire load analysis.
- Current and future loads. Heating, cooling, cooking, other vehicles and planned renovations all count.
- Charging requirements. Vehicle model, weekly kilometres and practical overnight charging time.
- Cable route. Where the charger will mount, garage access and distance from the panel.
- Installation environment. Indoor or outdoor rating, cable protection and parking position.
A licensed electrical contractor can turn that into an actual design rather than a guess based on internet comments.
Ontario rules: don't skip this step
Ontario's Electrical Safety Authority says EV charger installations require an ESA notification of work before installation. If you hire someone, they must be a Licensed Electrical Contractor.
Look for a recognised approval mark on the charging equipment and use a solution suited to the installation environment. An electrician should also confirm the current Ontario Electrical Safety Code requirements.
See the ESA's EV charging guidance for the official homeowner requirements.
A useful question before you spend money
“How many kilometres do I normally drive in a day, and how long is my car parked at home?”
A household driving short daily distances may not need the maximum available Level 2 charging speed. Correctly sizing the experience—not just the circuit—can avoid unnecessary cost.
Your next step
Before buying the charger, send Great Lakes Electric your vehicle model, preferred charger, panel photo (door closed) and approximate charger location.
They can help you explore EV charger installation in Sarnia and whether panel work is part of the scope.
Frequently asked questions
Will a 40-amp charger work on a 100-amp service?
Possibly, but the service rating alone cannot answer that. The allowable installation depends on a load calculation and any approved load-management approach.
Is a 200-amp panel better for two EVs?
Two vehicles can increase the load, but managed charging and actual driving habits may affect the best solution. Have the full plan assessed.
Do I need an ESA permit for home charging equipment?
Yes, ESA states an electrical notification of work is required for charger installation. The contractor performing the work should handle it.
Should I buy the charger before calling an electrician?
It is often better to check the panel, location and equipment compatibility first, so you don't purchase a unit that complicates installation.
Sources & further reading
Official Ontario safety guidance and, where applicable, published market-price examples. Pricing is not a Great Lakes Electric quotation.