They are commonly used for connecting solar panels. MC4 stands for “Multi-Contact, 4 millimetre”. It is a standard in the renewable energy industry. An MC4 connector enables the easy construction of strings of panels.
They also come UL-rated and resistant to damage by UV rays. Many reasons explain the popularity of the MC4 connector. Apart from its UV resistance and weatherproof construction, the MC4 connector is easy to install. It also uses a latching construction that prevents a connection from disengaging unexpectedly.