Danger of chopping MC4 extension cables in half

[bolhuijo]

As I was planning my panel layout, I knew I had 2 strings and needed about 100 feet of wire. I also knew I only needed MC4 connectors on one end because the other end of the wires lands on a bus bar in the combiner box. Genius me bought a pair of 100 foot MC4 extension cables and snipped them in the middle to make 2 pairs of 50 foot cables. So far so good.
While plugging in one of the connectors, I noticed I was plugging in a red cable to a connector marked '-' on a panel. Only then did the solar powered light bulb over my head go on. My MC4 extension cables of course had male on one end and female on the other. I was pretty close to landing 1 string in my combiner box reverse polarity.
Smoke avoided.

 

[v_green57]

Which is why I ALWAYS apply the DVM to the connectors to cross check. Even on brand-new panels.

 

[dougbert]

trust but verify

 

[efficientPV]

I just installed an outdoor disconnect with MC-4 in and out. I removed the out connectors and wired directly to the disconnect. Now I have two cable ends where the colors are wrong. Just hope I remember. Just make sure your red and black meter leads are in the right sockets!

 

[underdog5004]

Same thing happened to me. I ran an extension cable from the panel on top of my truck to the charge controller under the hood and I couldn't understand why it seemed like my battery wasn't charging very quickly or at all. Luckily the Morning Star sunsaver is reverse polarity tolerant to a degree so no damage was done.

 

[wildbillpdx]

I purchased cables to do the same, but I replaced the MC4 connectors on the cut ends. Never planned to use the raw cable for connections so I never had any issues.

 

[KITROBASKIN]

Easy enough to place red tape on the positive end of the black cable, black tape on the negative end of the red cable?

 

[dougbert]

Easy enough to place red tape on the positive end of the black cable, black tape on the negative end of the red cable?

I ALWAYS buy RED and BLACK conductors as a set.

Been there, done that with same color conductors - same price so why not?

 

[upnorthandpersonal]

I ALWAYS buy RED and BLACK conductors

Same. I cringe every time I see people build battery systems with orange cable and some tape to indicate positive and negative...

 

[bolhuijo]

Same. I cringe every time I see people build battery systems with orange cable and some tape to indicate positive and negative...

I have some orange cables that came with my battery. I think I will write "red" and "black" on them with a sharpie.

 

[Lprantner]

As I was planning my panel layout, I knew I had 2 strings and needed about 100 feet of wire. I also knew I only needed MC4 connectors on one end because the other end of the wires lands on a bus bar in the combiner box. Genius me bought a pair of 100 foot MC4 extension cables and snipped them in the middle to make 2 pairs of 50 foot cables. So far so good.
While plugging in one of the connectors, I noticed I was plugging in a red cable to a connector marked '-' on a panel. Only then did the solar powered light bulb over my head go on. My MC4 extension cables of course had male on one end and female on the other. I was pretty close to landing 1 string in my combiner box reverse polarity.
Smoke avoided.

I have two bags of MC4 connectors, and never use them. I just wire up the panels in series and parallel as required, then use butt connectors with shrink tube, as Will does. Most of my panels are fitted with Canadian style MC4's anyway, so I just plug them into each other, and at the end of the string, I just butt splice and shrink wrap the remaining two or four connectors and run the cables as I need. Works for me! The MC4's that are common on Amazon DO NOT FIT THE CANADIAN MC4'S! Not really a big deal anyway, and I am not yelling. I just type in all caps to make a point. Cheers!

 

[Bananaman321]

Personally I'd rather just have all black wire and that would eliminate the confusion you would have to test it to verify and then you could color tape market it when terminating cable.

 

[LeeStanphill]

I wouldn't mix colors on a customer rig, but on my personal stuff I've mix and matched to save money, but put a piece of color appropriate heat shrink or electrical tape on the last 6" or so..

Even in Grand design RV's, they run Red from battery+ to the disconnect, then black returning from the disconnect (Which is still +12V and it's black where it hits the + Bus bar.. I was scratching my head at that logic.

Always good practice to verify everything with a meter before connecting, and like efficient PV said, be sure you meter leads are in the right socket lol.. I've let the magic smoke out of the box with that mistake before.

 

[KITROBASKIN]

I ordered MC4 to PowerPole custom cables (Powerwerx) and specified female positive on the MC4, yet there was no indication of that designation in the order or receipt. Now I have a red cable doing the job of a black cable going from panels to the charge controller. Could have been my mistake?


Ended up with this:

 

[LeeStanphill]

Ignore all colors, and if the conductor from the negative side of the PV makes it to the negative side of the MPPT, and the positive makes it to the positive, you are fine.

Pretend you are colorblind, and just make it work

 

[Bananaman321]

Ignore all colors, and if the conductor from the negative side of the PV makes it to the negative side of the MPPT, and the positive makes it to the positive, you are fine.

Pretend you are colorblind, and just make it work

100% agreed regardless of color coding always test and then test again before you throw that switch.

Check your meter and your leads as well
Verify with any dc battery is a good +- check.

 

[SparkyJJO]

I have some orange cables that came with my battery. I think I will write "red" and "black" on them with a sharpie.

Red cables with the word "black" in black sharpie, and black cables with "red" written in red sharpie.

 

[Bananaman321]

I wouldn't mix colors on a customer rig, but on my personal stuff I've mix and matched to save money, but put a piece of color appropriate heat shrink or electrical tape on the last 6" or so..

Even in Grand design RV's, they run Red from battery+ to the disconnect, then black returning from the disconnect (Which is still +12V and it's black where it hits the + Bus bar.. I was scratching my head at that logic.

Speaking of RVs I have a 1993 36' Rockwood Embassy and other than the 2 main battery cables the entire bus is wired with blue gray wiring of the same size for pretty much all of the circuits including the engine and transmission wiring And being that it's of age most of the identification is gone needless to say I'm probably going to end up rewiring almost the entire thing mainly so I can sleep good at night. Plus should also simplify maintenance if there be a problem.

 

[LeeStanphill]

Red cables with the word "black" in black sharpie, and black cables with "red" written in red sharpie.

When in doubt, paint it black and put it to ground

 

[JWLV]

I always use a small piece of red heat shrink tubing on any cables that I cut. Heat shrink tubing lasts a lot longer than a piece of tape.

 

[robbob2112]

Speaking of RVs I have a 1993 36' Rockwood Embassy and other than the 2 main battery cables the entire bus is wired with blue gray wiring of the same size for pretty much all of the circuits including the engine and transmission wiring And being that it's of age most of the identification is gone needless to say I'm probably going to end up rewiring almost the entire thing mainly so I can sleep good at night. Plus should also simplify maintenance if there be a problem.

Now all you need are 42 miles of blue-gray wire and a wire labler that prints on wire sheath

Or maybe 42 color combinations in different sizes and a lable make that prints on shrink-wrap.

 

[Bananaman321]

Now all you need are 42 miles of blue-gray wire and a wire labler that prints on wire sheath

Or maybe 42 color combinations in different sizes and a lable make that prints on shrink-wrap.

Plan is to build a new wiring harness for the engine transmission and related components and then rewire the house portion all to AC line voltage with a solar system and AIO powering it. The two systems will only be linked by their earth ground bond to frame and a isolated DC to DC charge controller to maintain the vehicle battery. 3.7k solar 3k inverter 5-15kwh LPH plug-n-play EG4 server batteries.

 

[Suijkerbuijk]

I have make me own cable and if you look to the picture
Are all black wires
But one have red shrinking on them that is the + side.

Yes i know i still have to replace the victron 100/50 cable for bigger one
Its now limit to max 20a
Its a 6mm2 cable and have to replace to 16mm2 what i have .
Just waiting for other parts that are not here .
So i can do it in one run.
Not easy to go in to engine room upside down to do your work.

 

[crossy]

I make my own cables, and even after fitting zillions of MC-4s I still have to think carefully which sex goes where. Is that +ve going towards the SCC or from the panel? All my panel interconnects are black. The only red cables are from panel +ve to SCC. I use a lot more black cable than red for some unknown reason.

Related anecdote.

Long, long, ago our Machines and Control lecturer at uni was a chap called Mr (Fray Bentos) Bentley. Superb lecturer but he had one small quirk.

The labs had racks of red, blue and yellow cables used to wire up your experiments, you followed the lab-sheet then Fray Bentos checked it before you could power it on (even so there was the occasional bang!).

If old Bentley found a terminal with both a red and a blue wire on it (there were never enough of each colour available) he would wave his arms around and jabber incoherently whilst simultaneously disconnecting every wire in your carefully set up experiment!

Sadly, he was knocked off his bicycle and killed not long after I finished my degree, but I have him to thank for knowing exactly how a Ward-Leonard speed control or that wonderful device the Schrage-motor works!! (you would never find either in a modern system of course)

 

[HRTKD]

I was preparing to create a PV extension cable today and sat there trying to figure out which connector to put on which wire (red/black). I got distracted and worked on other tasks and haven't made any progress on the extension cable.

My line of thinking is that it doesn't really matter which connector goes on which wire as long as the other end of the wire uses the opposite connector. So on the positive wire, a male connector goes on one end and female on the opposite end.

Prove me wrong.

I gave away two PV extension cables with my RV when I sold it a week ago. Now I'm wishing that I hadn't been so generous and had kept one of the extension cables.