MC4 system consists of a plug and socket design. The plugs and sockets are inside plastic shells that appear to be the opposite gender – the plug is inside a cylindrical shell that looks like a female connector but is referred to as male, and the socket is inside a square probe that looks male but is electrically female. The female connector has two plastic fingers that have to be pressed toward the central probe slightly to insert into holes in the front of the male connector. When the two are pushed together, the fingers slide down the holes until they reach a notch in the side of the male connector, where they pop outward to lock the two together.
For a proper seal, MC4s must be used with cable of the correct diameter. The cable is normally double-insulated (insulation plus black sheath) and UV resistant (most cables deteriorate if used outdoors without protection from sunlight). Connectors are typically attached by crimping, though soldering is also possible.
The MC4 connector is UL rated at 20 A and 600 V maximum, depending on the conductor size used. Standards efforts in Europe also allow 1000 V versions.