There is a difference between the physical capacity of an electrical panel and its actual electrical capacity.

Physical capacity is simply the number of available slots for installing circuit breakers. A panel may appear “empty” with several free slots, giving the impression that new circuits can easily be added. This can cause problems if the electrical capacity is not considered. Electrical capacity depends on the maximum current the panel can handle, usually determined by its main breaker (100A, 200A, etc.).

Electrical capacity, on the other hand, is calculated based on the total load of the building. It is not simply the sum of the installed circuit breakers, but rather an estimate based on specific calculations from the electrical code.

For example, a 200A panel may be far from full, but if the house already uses several high-power loads such as a central furnace, a hot tub, sauna & pool, a charging station, and a stove, the maximum demand may already be approaching its limit. Adding a new circuit in this context can cause the main breaker to trip, even if there is physical space available.

It’s also important to understand that the main breaker is not designed to operate continuously at its maximum capacity. While it’s technically possible to reach 200A on a 200A panel, in practice, this generates heat, puts stress on the components, and increases the risk of tripping. A well-designed system aims to maintain an 80% safety margin.

Finally, the presence of free space in a panel should never be the sole criterion for adding loads. A thorough assessment requires a complete load calculation. If there is insufficient electrical capacity, solutions can range from intelligent load management to a complete panel or service entrance upgrade.