A flat cover protects the device only when nothing is plugged into it. An in-use cover, also called a bubble cover, allows a cord to stay connected while keeping the assembly weatherproof, and the NEC requires it for most exterior receptacles. Depth of the cover has to clear the plug and the cord bend, and the box has to match the mounting — a one-gang box takes a one-gang cover.
This group includes cast aluminum and PVC weatherproof boxes, single and double gang, with in-use covers in horizontal and vertical orientations.
