What is a load calculation and why does my electrician need to do one?

A load calculation is a detailed assessment of how much electrical demand your home places on its panel and service entrance, and your electrician needs to do one before any major electrical addition to ensure your system can safely handle the new load. Without a load calculation, adding a high-draw circuit like an EV charger, hot tub, or electric range could push your panel past its rated capacity, causing chronic breaker trips or creating a fire hazard.

The calculation follows a specific method outlined in the Ontario Electrical Safety Code. Your electrician adds up the wattage of every electrical load in your home, including general lighting and outlets, kitchen circuits, laundry circuits, heating and cooling equipment, water heater, dryer, range, and any other fixed appliances. The code applies demand factors that account for the fact that not everything runs simultaneously. For example, your oven and your air conditioner rarely operate at the same time at full capacity. After applying these demand factors, the result is your home's calculated electrical demand in amps. This number is then compared against your panel's rated capacity.

In practical terms, load calculations matter most for GTA homeowners in three common scenarios. The first is EV charger installation. A Level 2 charger draws 40 to 50 amps continuously, which is a massive load to add to any panel. If your home has 100 amp service and your calculated demand is already at 80 amps, you cannot safely add a 40 amp EV charger without upgrading to 200 amp service first. The second scenario is adding central air conditioning to a home that previously had window units. A central AC system draws 20 to 30 amps, and in post-war homes across Scarborough, North York, and the inner suburbs with 100 amp panels, this addition often requires careful analysis. The third scenario is basement apartments or suites, which are increasingly popular across the GTA. Adding a full kitchen, bathroom, and living space with its own electrical demands requires a formal load calculation to determine whether a sub-panel can be fed from the existing service or whether a service upgrade is needed.

A load calculation typically costs $150 to $300 as a standalone service, though most electricians include it in their quote for panel upgrade or major circuit work. The ESA may require documentation of the load calculation as part of the permit process for major additions. If you are planning any significant electrical addition, Toronto Electrical Repair can match you with a licensed electrician who will perform a proper load calculation before recommending any work.