Do I need to upgrade my 100-amp electrical panel for an addition in Ottawa?

If your home still runs on a 100-amp electrical service, an addition is a good time to check whether it has enough capacity. Older homes often have smaller services, and the extra circuits an addition needs can push an existing panel past what it can safely supply. Whether yours needs an upgrade depends on a load calculation, not on the number on the main breaker alone.

Think about what the panel already supplies: the furnace, air conditioning, kitchen appliances, lighting, laundry and receptacles throughout the house. An electrician calculates the demand of those loads under the Ontario Electrical Safety Code. A house with central air, an electric dryer and an electric range may have little headroom left.

An addition adds load. Bathrooms, kitchen counters, electric ranges, dryers and heat pumps each need their own dedicated circuits, and even a simple bedroom or family room needs lighting and receptacle circuits plus smoke and carbon monoxide alarms. Ask your electrician to add the proposed circuits to the existing calculated demand and show you the result.

If the calculation shows you're short, the usual fix is a service upgrade, often to 200 amps. That involves replacing the panel, the meter base and the service entrance conductors. The utility (Hydro Ottawa) has to disconnect and reconnect the supply, so there will be a planned power interruption on the changeover day. Ask your electrician how long to expect. Electrical work requires an ESA notification or permit and is done by an electrical contractor licensed by ESA. A building permit is not required for work that is exclusively electrical, but your addition itself will have one.

Timing the upgrade well can save money. If the new panel goes in at the start of the project, the electrician can plan enough breaker spaces for the existing circuits and every new addition circuit, instead of returning later for a second job. Ask for the panel upgrade and the addition wiring in one quote.

Some people ask whether they can feed a sub-panel in the addition from the existing service instead. That can work, but only if the load calculation shows enough spare capacity for the new circuits. If you're already close to the limit, a sub-panel only moves the problem and you may end up upgrading later anyway as you add loads such as a heat pump or an electric vehicle charger.

You can check your current service rating on the main breaker or the panel label, but don't rely on that alone. Older panels sometimes have issues that only an electrician will spot. Ask electrical contractors for an itemized quote that shows the load calculation, the upgrade and the addition circuits separately, and check their authorization on the Skilled Trades Ontario Public Register.

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