The code requires a blank cubic inches of free space for each number 10 wire in an outlet box.

The requirement for the amount of free space in an outlet box is based on the National Electrical Code (NEC) regulations, which dictate how much space is necessary to accommodate the conductors safely and effectively. For each number 10 wire, the code stipulates that there must be at least 2.5 cubic inches of free space in the outlet box. This is to ensure proper wire management, prevent overcrowding, and reduce the risk of overheating or electrical failure due to insufficient space for heat dissipation.

In situations where multiple wires are present, having adequate space allows for easier installation and maintenance, reduces strain on the wires, and helps in maintaining electrical safety standards. The requirement is specific to number 10 wire, which can carry considerable current, thus necessitating this higher volume of free space compared to smaller gauge wires.