The MAINS ELECTRIC BOX, also known as the consumer unit or fuse box, is the brains in every UK home's electrical system. The mains electric box is a square or rectangular box made from plastic or metal that is installed somewhere in our homes. The incoming live electricity feed enters the home and passes through the electricity meter that monitors how much electric we use. In this article, we'll take a closer look at mains electric boxes - what they are, what they do, and why they are so important. What is a Mains. The distribution box (DB box) helps safely and efficiently distribute electrical power. It also contains safety devices such as fuses, circuit breakers, and residual current devices (RCDs) that protect you and your appliances from electric shocks. To choose a home distribution box, you must count your circuits and add 30% spare space.