Solar MC4 Connectors
These are solar MC4 connectors the FEMALE in on the bottom and the MALE plug is on top.. Today more and more solar panels are shipping with MC4 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 MC4 solar connectors are UL rated for 600V and up to 50A of maximum current, depending upon brand. The term MC4 stands for “Multi-Contact 4mm“. Multi-Contact is a German manufacturer and they invented the MC4 standard. MC4’s can also range from IP65 to IP68 rated, also depends upon brand, which means they are fully “dust & water jet tight” (IP65) and can be submersed to 1 meter for 1 hour and still retain water resistance (IP68). The MC4 connectors are available in 14, 12, 10 & 8GA sizes.
14GA = 22.5A
12GA = 37A
10GA = 43A
8GA = 50A
MC4’s work quite 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.
NOTE: Please click on any image to make it larger.
MC4 FEMALE / + Positive
These are the individual pieces of the FEMALE MC4 connector:
From Left to Right:
- Compression Nut
- Gland Compressing Ring
- Water Tight Sealing Gland
- MC4 FEMALE Crimp Terminal
- MC4 FEMALE Plug Body
MC4 MALE / – Negative
These are the individual pieces of the MALE MC4 connector:
From L to R:
- Compression Nut
- Gland Compressing Ring
- Water Tight Sealing Gland
- MC4 MALE Crimp Terminal
- MC4 MALE Plug Body
FEMALE & MALE
The FEMALE terminal on the left is ready to connect to the MALE terminal on the right.
Insert FEMALE into MALE
I know it’s a bit confusing, the FEMALE vs. MALE with MC4’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 plastic housing not the physical 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.
Press & Snap Closed
You just press the two MC4’s together until the snap closed.
MC4 Assembly & Disassembly Tool
These are the tools used for snugging the MC4’s together. They are inexpensive, and worth having, especially for taking the terminals apart after they have been closed for a while.
MC4 Crimp Dies
Here’s where the extra tool cost, that I mentioned earlier, comes into play. You will need a crimp tool for the MC4 terminals. However, as usual, I have located a very good value in an MC4 crimping tool, though not the tool pictured.
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 more expensive pro-grade versions, which utilize a locator assembly. For the money this tool preforms very, very well.
In full disclosure I imported a reasonably priced MC4 die set and crimping frame from Taiwan and while the dies are not pro-level you’re not paying pro level pricing either. The tool represents a decent value for the budget minded boater. The tool can be found in the; Marine How To Web Store
MC4 Crimp Dies Closed
Like a D-Sub style crimp tool the MC4 dies make a “B” or “butt-cheek” type crimp. The pictured die set is sized for 10, 12 & 14 AWG wire as well as 2.5 mm², 4 mm² and 6 mm² wire.
Strip Outer Jacket From Cable
On boats I will occasionally use a two conductor un-tinned round cable such as an SO type wire for the external connections to the solar panel, but most often a tinned marine grade wire is what I use.
Inside the solar MC4 terminal the use of tinned wire is not as critical as with open style crimps. I almost always use 10/2 or 8/2 wire from the panel to deck if using MC4’s. Once through a deck-gland, such as those made by Scanstrut, and into the vessel, you can switch to a larger GA wire in order to minimize voltage drop on longer runs from the PV to the battery bank.
In this image I’ve stripped back the outer jacket of the wire exposing the inner 10GA conductors.
Slide Heat Shrink Over Cable
To give the wire a nice finished look and feel I slide some adhesive lined dual-wall heat shrink over the wire. Be sure to do this before you install the MC4’s.
Slide MC4 Parts Over Cable
Next, slide on the compression nut, compressing clamp and watertight seal, in this order.
Strip The Wire
Now strip back about 1/4″ +/- of wire being very careful not to damage any strands.
Check Your Strip-Depth
Insert the stripped wire into the MC4 crimp terminal and check your strip depth.
I prefer to have the stripped wire extend very slightly into the barrel of the terminal a bit. This ensures it does not fan out when crimped, and create issues when inserting it into the plug.
Insert Terminal Into Crimp Tool Dies
You’re now ready to place the terminal into the crimp tool dies. The open wing-ends of the terminal face up towards the butt cheeks so it can be rolled over and formed to execute the crimp.
TIP: It helps to compress the crimp frame just a click or two. This will hold the terminal as shown and you can then insert the wire and finally squeeze the handle to complete the crimp. Professional level MC4 crimp tools such as those by AMP, Rennsteig and others, use a locator that holds the terminal for you.
Crimped MC4 Terminal
Even non-pro-level MC4 crimp tools can make a decent & suitably 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 can “fan out” and make inserting it into the plug a bit difficult.
Insert the Terminal Into the Plug Body
Once you’ve crimped the wire to the terminal you can then insert the terminal into the MC4 plug body. Keep pushing until you feel or hear it click.
Press it in Until it Clicks
Keep pressing the crimped terminal into the plug body until you feel it “click” into place. With some cheap knock off MC4 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.
WARNING: I strongly recommend the use of branded Multi-Contact MC4 terminals. The MC4’s coming out of China these days is mostly horrendous and it’s a full blown crap-shoot as to what you are getting in terms of quality. I’ve seen numerous knock-off MC4 terminals FAIL by becoming brittle due to UV exposure. I have never once seen this with genuine Multi-Contact MC4’s. Yes the Multi-Contact brand of terminals cost more, but they are the real McCoy.
Slide Sealing Gland Into The Plug Body
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.
Thread On Compressing Nut & Tighten
Thread the nut on finger tight then just snug it up, as shown, using the MC4 tool.
Finished MC4 Plug
Here’s the finished MC4 connector.
Good luck & happy boating!
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