Part 1: Choosing the Correct Wire Size for a DC Circuit May 19, 2010In addition, the DC Wire Selection Chart shown below assumes a wire insulation rating of 105°C. A lower rating will decrease the current-carrying capacity of the wire. To use the chart included with this technical brief, follow the instructions below. Choosing the correct wire A Locate the CURRENT IN AMPS of your appliance across the top of the chart. Most electrical products include a rating label, Wire Sizing Tool for 12, 24 and 48 Volt DC Systems | altE How to Size Wiring for Your System - The Manual Method. In conventional home electrical systems (120/240 volts ac), wire is sized primarily for safe amperage carrying capacity (ampacity). The overriding concern is fire safety. In low voltage systems (12, 24, 48VDC) the overriding concern is power loss.