What is an MC4 connector?

What is an MC4  connector?
MC4 stands for “Multi-Contact, 4 millimeter” and is a standard in the renewable energy industry. Most larger solar panels come with MC4 connectors already on them. It is a round plastic housing with a single conductor in a paired male/female configuration developed by the Multi-Contact Corporation. Multi-Contact is the official manufacturer of MC4 connectors. There are many other manufacturers producing clones (why this matters will be discussed later in this article).

The maximum current and voltage that can be pushed through MC4 connectors varies by application and the type of wire used. Suffice it to say that the margin of safety is quite large and more than adequate for any foreseeable project an amateur radio operator may undertake.

MC4 connectors terminate to each other with a notched interlock that in some situations requires a special tool to disconnect. The interlock prevents the cables from being unintentionally pulled apart. They are also weather resistant, UV proof,  and designed for continuous outdoor use.

When and where MC4 connectors are used.
Small solar panels under 20 watts typically use screw/spring terminals or some type of automotive electrical connector. These panels do not produce high currents and are intended to be used as stand-alone units, so the method of termination is not really important.

Larger panels or panels that are designed to be wired together in an array need a standardized termination that can handle higher power levels. The MC4 connector fits the need perfectly. They are found on nearly every solar panel greater than 20 watts.

Some hams will cut the MC4 connectors off the solar panel and replace them with Anderson Power Poles. Do not do this! Power Poles are not designed for long term outdoor use, and you will have a solar panel that is not compatible with any other solar panel. If you insist on using Power Poles, make an adapter with an MC4 on one end and a Power Pole on the other.