The foundational formula is $Power (Watts) = Voltage (Volts) times Current (Amps)$, or $P=V times I$. To determine the necessary capacity, sum the wattage ratings of all equipment that will operate simultaneously and divide that total by the source voltage to find the minimum. Before we dive into calculations, let's get familiar with a few essentials: 1. Your Project's Total Power Demand This isn't just adding up wattages randomly. Think of your home as a busy kitchen—not every appliance runs at once. Review fill usage and spare capacity. Available volume = listed box volume or estimated inside dimensions + extension volume + raised cover volume - deductions. Related Post: How to Determine the Right Size Capacity of a Subpanel?As a leading manufacturer of high- and low-voltage electrical equipment that strictly follows the IEC, GB/T, and ISO9001 standards, Chuanli specializes in producing high-performance cable distribution boxes, including outdoor equipment and customized distribution boxes solutions. This article will. Design Distribution Box of one House and Calculation of Size of Main ELCB and branch Circuit MCB as following Load Detail. Power Supply is 430V (P-P), 230 (P-N), 50Hz. 6 for Non Continuous Load & 1 for Continuous Load for Each Equipment. Branch Circuit-1: 4 No of 1Phase. The Electrical Box Calculator is a simple yet powerful online tool designed to help electricians, engineers, technicians, and DIY users quickly determine the internal volume of an electrical box along with its recommended safe fill capacity.