These are solar MC-4 connectors the FEMALE on the bottom and the MALE plug on top.. Today more and more solar panels are shipping with MC-4 terminals and less and less with actual junction boxes. I still personally prefer a water tight j-box, and water tight gland nut, but not all panels ship that way.
The MC-4 solar connectors are UL rated for 600V and 30A of current they are also IP68 rated which means they are fully "dust tight" and can be submersed to 1 meter and still retain water resistance.
They work well but on boats but if not carefully installed they can be a tad bulky and prone to being caught on things. That said, they are one of the better water tight electrical connections available for marine use. You don't have to use them only on solar connections and they could certainly be used for other applications.
Like any other project on boats this project will add yet another tool to your tool box.
Solar MC-4 Connectors
These are the individual pieces of the FEMALE MC-4 connector:
From Left to Right:
Gland Compressing Ring
Water Tight Sealing Gland
MC-4 FEMALE Crimp Terminal
MC-4 FEMALE Plug Body
MC-4 FEMALE / + Positive
These are the individual pieces of the MALE MC-4 connector
From L to R:
Gland Compressing Ring
Water Tight Sealing Gland
MC-4 MALE Crimp Terminal
MC-4 MALE Plug Body
MC-4 MALE / - Negative
The FEMALE terminal on the left is ready to connect to the MALE terminal on the right.
FEMALE & MALE
I know it is confusing, the FEMALE vs. MALE with MC-4's, because the one on the left clearly looks like a MALE and the one on the right clearly looks like a FEMALE.
The terminology relates to the crimp terminals inside the plugs not the body of the plugs. The plug on the right has the small male "pin" and the plug on the left has the FEMALE barrel/receptacle.
Insert FEMALE into MALE
You just press them together until they "snap" closed.
Press & Snap Closed
These are the MC-4 assemble and disassemble tools. They are inexpensive and worth having especially for taking the terminals apart after they have been closed.
MC-4 Assembly & Dissasembly Tool
OK here's where the extra tool cost comes into play. You will need a crimp tool for these terminals. However, as usual, I have located a very good value in an MC-4 crimping tool. A pro who does this every day for a living would not use this tool because it is more tedious and time consuming than the $1000.00 versions, but for the money, this tool preforms very, very well.
I bought this MC-4 die set and crimping frame from Pro's Kit:
Pro's Kit Lunar Series Crimp Frame (LINK)
Pro's Kit Lunar Series MC-4 Die Set (LINK)
All together the crimp frame and die set will run you $51.52 a real STEAL for an MC-4 crimp tool. Plus you will now be able to buy more individual die sets for other crimping jobs. Pro's Kit accepts PayPal so no diffing to find your credit card..
MC-4 Crimp Dies
Like a D-Sub crimp tool the MC-4 dies from Pro's Kit make a "butt-cheek" crimp. The die set is sized for 10, 12 & 14 AWG wire as well as 2.5 mm˛, 4 mm˛ and 6 mm˛ wire.
MC-4 Crimp Dies Closed
I will generally use a two conductor round cable such as an SO type wire for the external connections to the solar panel. I almost always use 10/2 wire. Once through a deck gland and into the vessel you can switch to a larger GA wire to minimize voltage drop.
Here I have stripped back the outer jacket of the wire exposing the inner 10GA conductors.
Strip Outer Jacket From Cable
To give the wire a nice finished look, and feel, I slide some adhesive lined heat shrink over the wire before I install the terminals.
Slide Heat Shrink Over Cable
Next, slide on the compression nut, compressing clamp and watertight seal in this order.
Slide MC-4 Parts Over Cable
Now strip back about 1/4" +/- of wire. Be very careful not to damage any strands.
Strip The Wire
Insert the stripped wire into the crimp terminal and check your strip depth.
I prefer to have the stripped wire extend into the barrel of the terminal a bit so it does not "fan out" when crimped and create issues when inserting it into the plug body.
Check Your Strip Depth
Now you're ready to place the terminal into the crimp tool dies. The open end of the terminal faces up towards the "butt cheeks" so it can be rolled over and formed to execute the crimp.
It helps to compress the crimp frame a couple of clicks. This will hold the terminal as shown and you can then insert the wire and finally squeeze the handle to complete the crimp.
Insert Terminal Into Crimp Tool Dies
For an inexpensive MC-4 crimp tool it really makes a nicely executed and strong crimp. This picture illustrates why I like to see the stripped wire extend into the barrel slightly. If it does not extended into the barrel of the terminal it tends to "fan out" and make inserting it into the plug body difficult.
Once you've crimped the wire to the terminal you can then insert the terminal into the MC-4 plug body.
Insert Terminal Into Plug
Keep pressing the crimped terminal into the plug body until you feel it "click" into place. With some MC-4 terminals this is less obvious than with others.
Don't worry about mixing up the terminals and plug bodies because male & female pins will not fit into the wrong plug bodies.
Bear in mind that solar panels ship with the female plug shown here, marked +, on the positive output lead from the solar panel. This means the positive wire on your boat will get the corresponding male plug not another female plug.
Press Until It Clicks
Once the terminal has been clicked into place slide the sealing gland and compression gland up the wire and into the plug. The gray colored sealing gland (not all brands use gray) should be "in" the terminal as shown here.
Slide Sealing Gland Into The Plug Body
Thread the nut on finger tight then snug it up, as shown, using the MC-4 tool.
Thread On Compressing Nut & Tighten
Here's a finished MC-4 connector.
Finished MC-4 Plug
Good luck with your project!