Solar MC4 Connector

Description

MC4 connectors are single-contact electrical connectors commonly used for connecting solar panels.

The 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 both UV and higher temperature resistant (most cables deteriorate if used outdoors without protection from sunlight). Connectors are typically attached by crimping, though soldering is also possible.

Wiring MC4 Equipped Modules in Series:

If you have two or more solar modules to wire in series, the MC4 connectors make it very simple. Take a look at the first module and you’ll notice that it has two wires extending from the junction box. One wire is the DC positive (+) and the other is the DC negative (-). Generally, the female MC4 connector is associated with the positive lead and the male connector is associated with the negative lead. This may not always be the case, so it’s always a good idea to look at the markings on the junction box or test the polarity with a digital voltmeter. A series connection is when you wire the modules together by connecting the positive lead on one module to the negative lead on another module. The male connector will snap directly into the female connector. Here’s a simple diagram illustrating this.

As you can see, the two modules are now connected together by the two leads. This increases the voltage of the circuit. For example, if your modules are rated for 18 volts at maximum power (Vmp), then two of them connected in series will measure 36 Vmp. If you connected three modules in series, the total Vmp would be 54 volts. The current at max power (Imp) will be constant when wiring a series circuit.

Wiring MC4 Equipped Modules in Parallel: Parallel wiring requires the positive leads to be connected together and the negative leads to be connected together. This method will increase the current at max power (Imp) while keeping the voltage constant. For example, let’s say your modules are rated for 8 amps Imp, and 18 volts Vmp. If you connect two of them in parallel, your total amps would be 16 amps Imp and the voltage would remain at 18 volts Vmp. When wiring two or more modules in parallel, you will need some additional equipment. If you’re only using two modules, the easiest method is to use MC4 multibranch connectors. You obviously can’t connect two male connectors or two female connectors together, so we use the multibranch connectors to accomplish that. There are two different multibranch connectors. One type accepts two male MC4 connectors on the input side and has a male MC4 connector for its output. The other type accepts two female MC4 connectors and has a female MC4 connector for its output. Essentially, you’ve stepped down the number of wires from two positive and two negatives to one positive and one negative. Here’s a diagram so that you can see what it’s doing.

If you are paralleling more than two modules or you’re paralleling strings of modules, that requires a device called a PV combiner box. You no longer need the multibranch connectors because the combiner box will be performing the same function. The multibranch connectors are only suitable for paralleling two modules together. If you need to connect more than two modules or strings in parallel, a combiner box is used. The total number of modules that can be combined will depend upon the electrical rating and physical size of the combiner box.

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