MC4 Connectors

I setup a small solar system in my workshop a couple of years ago, and one thing I needed was custom cables. Did a bit of research then bought cable, MC4 connectors, and a proper crimper. And I took photos one day when I was upgrading some cables. I do live in Thailand and wire size here is square millimeter (mm2 or sqmm), not AWG. But there is plenty of online converters that can do the conversion for you. The wire size I use is 6 mm2 which is 10 AWG.

With this Instructable I am not creating anything, simply using tools and parts that are readily available to you how to make reliable connections on custom wire lengths.

This is longwinded but I like to be thorough and show folks proper ways to do things instead of guessing or winging it.

Cable - stranded, either 6mm2 or 10 AWG, solar rated wire, meaning it is double-insulated, UV, and higher temperature resistant. Red for Positive and Black for Negative.

MC4 Connectors

MC4 Crimper, jaw number LS-2546B, ratchet type.

Cable Cutter

Non-contact Wire Stripper

MC4 Spanners

You need a good quality heavy duty cable cutter, as cutting through a solar cable is not like cutting a 14 AWG wire with thin insulation. The insulation is quite thick and a heavy duty cutter will make a clean cut through solar cable like a knife through butter.

A non-contact wire stripper is needed as well. Non-contact refers to the blades will not cut all the way through the insulation. The jaws of stripper clamp on the insulation and pull as the cutter goes into the insulation. For solar cable, due to the insulation thickness, it is recommended is to start a strip by applying pressure with the handles, release pressure, rotate the cable 90 degrees, then apply pressure again, release, rotate, then apply pressure to make the strip.

The crimper is specific to MC4 Connectors. If you have a set of ratchet type crimpers but not the correct jaw size, you may be able to order just a set of jaws, jaw number LS-2546B. The lower jaw has 3 positions for wire size, which is 2.5mm2, 4mm2, 6mm2 (10 AWG). I recommend using nothing less than 6mm2 for any small solar project.

The spanners can be used to tighten the nuts on the connectors as well as used to disconnect a set of connectors. Spanners come in plastic or metal. You are not torqueing on a tire with these, so the plastic ones are perfectly fine. There is a opening on the wrench end, this allows it to be slipped on a cable and the other spanner is used to hold the connector so you can tighten the nut.

The MC4 Connector is a waterproof electrical connector normally used to connect solar panels together. The MC stands for Multi-Contact which was one of the original manufacturers, and the 4 is the diameter, 4mm, of the male pin. The connectors can be fitted together by hand but require a tool to disconnect them. The shrouded pins and the requirement for a tool to disconnect was some of the safety specifications in their design.

In the US, contact your local electrical inspector as you may have a requirement that the connectors you use can be any brand, but they have to be the same brand used throughout your build.

Photo 1. Male and female pins do not make sense with these types of connectors, as the female pin is actually in the male connector, and the male pin is in in the female connector. Top row, female pin, female connector on its side, visible is the red o-ring as well as the locking tabs. And the female connector sitting upright. Bottom row, male pin, male connector on its side, and the male connector sitting upright, visible is rectangular holes which is where the locking tabs will be inserted into.

Photo 2. For each of row, the part on the the left is the connector business end, in the middle is the rubber gasket for the cable, and on the right is the cap (nut) for the cable side. These are waterproof connectors, and you can see a red o-ring on the female connector on the top, that fits into the connector on the bottom.

Photo 3. One spanner is holding the connector, the other spanner is on the nut where the cable would be going into the connector. In reality, the nuts can be put on really tight using just your fingers, the spanners come in handy when removing a nut.

Photo 4. Here is two connectors connected, you can see the two tabs from the right connector inside the left connector to lock them in place, this prevents the connectors from coming apart, which under load is very dangerous. The prongs on the wrench will push them inwards to release them. Now for the word Stop on the side and the two arrows, it is telling you do not disconnect without knowing what you are doing, as these connectors should NEVER be disconnected under load.

Photo 5. The spanner prongs are pushed onto the locking tabs to squeeze them inwards.

Photo 6. When the spanner tongs are in place, grab both sides of the connector and wiggle them and they should come apart, and you can see the red o-ring as they start to come apart. Important, NEVER disconnect when there is a load on the solar panels!

I am using 6mm2 (10 AWG) solar cable here, which is the wire size is 6 square millimeters in diameter. Note the diameter of the cable itself is 6.23 mm in diameter, the double insulation is very thick! And cable diameter in inches is right about 1/4 inch.

Before stripping, place the nut on the cable, then place the rubber gasket.

You need to measure out the length of cable you need. General rule is keep the positive and negative cables equal length. It does not hurt to over estimate by a foot or so, this gives you some wiggle room if you have to remake connections.

Then strip the cable to the appropriate length for the male pin in this case, or for the female pin if assembling one of those. General rule is you want bare wire in the tab area and just inside the pin area, this is more important on the female pin than the male pin.

Keep in mind, MC4 Connector pins are meant to be crimped with correct crimpers only. These are not made to come part once the crimped pin is inserted in the connector.

I have seen videos where people used pliers and complained their connectors never fit together. I have seen videos where people smashed the tabs with pliers and soldered them, and complained the connectors were faulty. Never use pliers or solder these!

Photo 1. Place the pin in the appropriate slot in the crimper jaws, in my case I am using 6mm2 wire. You want the wire end of the pin flush to the side of the jaws, round part down, tabs upwards, then squeeze the crimper until you hear just 1 click, that locks the jaws and holds the pin in place. Now insert the stripped wire into the pin, with the insulation flush with the side of the jaws. Squeeze the handles until fully closed, then it will open to release the pin.

Photo 2. Properly crimped pin.

Photo 3. Hold the connector in one hand and insert the pin into the connector with the other, you should hear a click when it locks in place. Give the wire a tug, it should be secure in the connector.

Photo 4. Slide the rubber gasket into the connector, it should fit squarely in the connector.

Photo 5. Screw on the nut, tighten with fingers, it may go up to the connector.

Photo 6. Completed cable with both ends with connectors.

Photo 7. Four cables, two red, two black, completed.

I hope you find this Instructable informative and useful. This will be referenced in another Instructable for a small solar project.