IEC 61439 is a key international standard for low voltage distribution boxes. This standard gives you a clear framework for safety and reliability. Whether in a wireway or any other box, power distribution blocks installed on the line side of the service equipment shall be listed and marked “suitable for use on the line side of. NEC 314. 28: Requires junction boxes to be made of non-combustible materials like stainless steel, aluminum, or UV-resistant plastic. 16: Dictates volume size in cubic inches, requiring 18 cu in for 3 to 6 conductors and 20 cu in for 7 to 8 conductors. The box capacity table shown (page A-5) is reproduced in part from the NEC® as a quick reference and. A distribution box is the heart of any electrical system. Whether in a home or an industrial facility, this box keeps your electrical setup organized, functional, and efficient.