When calculating box fill, what additional consideration is given in the presence of a grounding conductor?

In box fill calculations, a grounding conductor is indeed treated as an extra conductor. The National Electrical Code (NEC) specifies that when determining the number of conductors in a box, grounding conductors must be included in the overall count. This is because they occupy space within the box and can affect the fill capacity. Each conductor, including the grounding conductor, takes up a specific volume within the box, and failure to account for it could lead to insufficient space for heat dissipation and could potentially lead to safety hazards.

By treating the grounding conductor as an additional conductor, the box fill calculations ensure that the total volume of all conductors—including the grounding conductor—is considered. This helps maintain compliance with safety regulations and ensures that the electrical installation is safe and effective.