How to calculate the cables and switches in a distribution box

Add conductor rows by AWG size and count, enter the number of devices, grounds, and cable clamps, then compare the total required volume against your box's listed capacity. Supports mixed wire sizes in the same box. Box Capacity (cubic inches) Check manufacturer markings or NEC. Learn how to calculate electrical box fill using NEC 314. Box fill is one of the most commonly missed electrical calculations on residential and light commercial. To correctly calculate box fill for an electrical box containing multiple switches, you must follow the provisions of National Electrical Code (NEC) Section 314. What is. Pro Insight: A well-planned distribution box feels like a silent partner—you only notice it when something's wrong. Your Project's Total Power Demand This isn't just adding up. [pdf]