MC4 Plugs, The Hardest Working Things In Solar.
If you’re not involved in the solar industry but wonder how millions of solar panels worldwide are connected to deliver clean energy, you might have too much spare time on your hands. Nonetheless, I’m glad you’re interested because, as I’m about to explain, this topic can be quite electrifying – particularly when an electrical fire or short circuit causes a catastrophic inverter failure.
MC3 Connectors: Early Plug And Play
Back in the days of yore, when solar panels were a quaint 75 watts each, measuring about 500 x 1200mm, and proudly made in Australia; they were all hard-wired. Picture this; actual junction boxes with screwed connectors on the back, from which you ran flexible conduits and then threaded cables between every panel. Read also : What’s the finest solar system in Australia?. It took hours and made laying panels flat on the roof impossible.
Before long, panels were rolling out with leads just over a metre long, allowing those 800 mm wide beauties to be linked up in a daisy chain. Array wiring took a quantum leap with the advent of MC3 connectors that simply pushed together. It was a revelation nearly as astounding as the price of MC3 tools. Two pairs of pliers for a staggering $1500!
While some installers would chop them off, crimp on some barrel terminals and apply heat-shrink tubing for insulation, we thought we were pretty special when we took delivery of the gear that let us properly crimp MC3 pins onto our array wiring, AND pull the rubber boots over the pins to finish them.
A non-compatible connector from Jaiwei PV panels with a novel junction box approach to barrel crimps on the array wiring.This was a far cry from watching that one bloke who’d faff around soldering pins. Watching him wear down his molars, chewing on the boots to soften them, then yoinking them on with needle-nose pliers was neither industry best practice nor, in my book, particularly sane.
Then Came MC4
While other styles of plugs came and went, the market soon chose a winner: a new and improved MC3 connector called MC4. To see also : array. Some argue it wasn’t the best plug for the job, but everyone soon became familiar with the feel of barbed plastic pins as they clicked their way into becoming the much-imitated industry standard.
In fact, the “compatible” MC4 connection became a real problem. With many different makers all trying to avoid patent infringements, the minor differences in plugs and pins meant that while they fitted together mechanically, electrically they didn’t connect properly, and most critically, they didn’t seal out moisture.
The result was so many burnt out connections that the next revision of the solar installation standard, AS5033, mandated that only plugs from the same maker could be mated together.
Mismatched brands were prohibited, and the style seen above with wings was banned because you don’t need a tool to open them. And you don’t want Harry homeowner opening one under load and getting blown off the roof.
How To Terminate MC4 Connectors Properly
I have seen MC4 plugs fitted by numpties who aren’t properly equipped with the tools or the brain power to realise they’re a danger to themselves and others. See the article : Sunnova expands its Solar + Storage providing to 9 new states. If the cable isn’t retained properly in the plug and it can be pulled out, then there’s a potential to kill someone or burn holes straight through an iron roof.
I like to use Lanox as a preservative on my own jobs. It will keep moisture at bay if the plugs are left open overnight. It stops corrosion of the metal contacts and ensures the “o” ring seal slides home easily without binding or curling up.
Genuine MC4 spanners will slip before the gland fitting is over-tightened.
Beware Of Crap MC4 Connectors
The very worst plug I’ve struck is this “How Full Star” piece of rubbish. It’s brand new and came out of the box broken, as you see it here. The junction box attached to an equally dubious Luxor solar panel had the same problem with cracked glands. The design is so sloppy it isn’t even compliant as being “touchproof” with a standard test finger. These crappy products are the reason we have standards.
Getting MC4 Connectors Right Really Matters
If your solar installer is not properly trained or does not take enough care to ensure these small connections are done correctly, you will soon discover that an equally small amount of moisture can bring your entire system to a halt.
When the inverter detects DC electricity from your array leaking to earth, it will switch off and, by law, send you an email to raise the alarm.
Join us in the coming weeks as I detail the calamities that lead on from badly fitted and poorly maintained solar power systems.