MC4 connectors a massive scandal

Hedges said:

Bolting ring terminals must be a lot of fun with 600VDC (well, I use 480Voc in my strings.)

My first system was same voltage and screw terminals in PV junction boxes, but Real Goods sold me a segmenting breaker so the array was divided in 6 parts during assembly. Only connected in series when breaker turned on.

Wiring UF cable between junction boxes (neutral carried the return), I inadvertently touched in a 100VDC loop and pulled a nice flame.

I like MC3/MC4. Just want them to be reliable. I will use pure Stabuli in my next few builds. Comes on the panels and on the RSD, just have to buy the right parts for the rest. (probably have a few random knockoffs in what newer panels I mounted in recent years, before I learned the Truth.)

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I will use pure Stabuli in my next few builds.

They started as a sound precision product , but the market is flooded wit Cheap Charlie knockoffs at 20% of the original price - fire risk on a roof. Difficult to find the genuine product available now (unless you are in Germany)

FWIW King Alumicon 18-10 AWG made of solid aluminium block? We know how well 6mm2 Al threads do on prismatic cells ???? You have to be gentle (use a digital torque wrench ) or the strip. In my experience I believe that you tighten these up once, any form of repeated use rapidly degrades the thread. They also have a tendency to seize up
Why these are recommended for Copper wires as well BTSOOM. Dont you have the potential to set up a serious electrolytic cell? especial in coastal areas?

Is this the "Goop" that is used? Its for Al aerials and their stuff? Looks like Al powder in Si grease?

kolek said:

I'm not working with live power. I start by opening the DC disconnect on the inverter at night. Then I disconnect one of the MC4 connectors so the array circuit is open and there's no chance of arcing. Then I do the work. Then I reconnect the last MC4 connector and finally reconnect the inverter to the array. At no point is there a chance of getting shocked or creating a DC arc. I'm not manly enough to work with live power.

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You're grabbing one conductor in the middle of a series string that has 400V to 600V between the ends.
You rely on no other point being grounded at the same time.

Ideally you would have a ground cable to clamp on each of the two wires prior to splicing them. Might be possible with those exposed crimp terminals.

Imagine if a crew was installing an array with multiple strings of panels, and two guys who were supposed to be wiring two different strings tried to work on two connections within the same string at the same time.

JBertok said:

Alternating Current which is effectively cycling on and off usually 50-60 times per second.

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Which is optimally effective at scrambling ions that control heart rhythm.

JBertok said:

277V AC. ... It was enough to disrupt cardiac rhythm, but I survived the ordeal with anecdotal recollection.

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Been there done that, at about 220Vrms.

Supervstech said:

I mean... if you arent dealing with aluminum wire, why use aluminconns?

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I have a few around here, ran the PV wire to my LV6548's temporarily with them when I pulled the EG4 6500EX's out. Neat little package, insulated housing and cheap. Worked well waiting for the replacement EG4 6500EX's to arrive, then waiting for the EG4 charge controllers after pulling the second pair of 6500EX's out.

Could have used wire nuts for temporary wiring. I liked these in case the wife was messing around in the basement.

Boron said:

FWIW King Alumicon 18-10 AWG made of solid aluminium block?

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Solid block of material, just like any other CU/AL rated terminal.

Boron said:

We know how well 6mm2 Al threads do on prismatic cells ???? You have to be gentle (use a digital torque wrench ) or the strip. In my experience I believe that you tighten these up once, any form of repeated use rapidly degrades the thread. They also have a tendency to seize up

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From reading those few sentences, you are speaking from a position of not actually using them but projecting you know all about them.

Boron said:

Why these are recommended for Copper wires as well BTSOOM. Dont you have the potential to set up a serious electrolytic cell? especial in coastal areas?

Is this the "Goop" that is used? Its for Al aerials and their stuff? Looks like Al powder in Si grease?

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Can be used either/or both.

Isn't your entrance panel rated CU/AL? And other components as well? You should yank those all out if the components are CU/AL rated because ya know it can't be good.

The very idea of handling anything over 48Vdc on a roof seems criminally negligent. For home buddies just dont entertain the idea IMHO. Panels used to be floating but armchair mandarins decide they should be earthed. I can understand that you have an exposed metal framework which may (downstream become linked to higher voltages by accident/mistake). One member said be sure to use your own temp trailing earth clamp lead - or otherwise check earth continuity. Looks good to me. You dont want a mains zap on a roof especially if working alone.

Hedges said:

You're grabbing one conductor in the middle of a series string that has 400V to 600V between the ends.
You rely on no other point being grounded at the same time.

Ideally you would have a ground cable to clamp on each of the two wires prior to splicing them. Might be possible with those exposed crimp terminals.

Imagine if a crew was installing an array with multiple strings of panels, and two guys who were supposed to be wiring two different strings tried to work on two connections within the same string at the same time.



Which is optimally effective at scrambling ions that control heart rhythm.




Been there done that, at about 220Vrms.

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Navy airplane load center - 440v, 400Hz....OUCH

robbob2112 said:

Navy airplane load center - 440v, 400Hz....OUCH

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Ahh, the sweet singing of 400Hz military power supplies. Tacfire systems used all 400Hz generators, two shelters, boa cables... Replaced with a briefcase before I got out, Probably a hand-held now.

Had my first failure of a MC4 connector and it was a pain to find. Mostly because symptoms were odd in that most of the time the array produced. But ever now and than it seem to be erratic . I was not sure if the PowMr AIO was to blame . But the last few days I was getting a beep alarm during the day followed by another beep a few seconds later and noticed on the screen that production was zero for a few seconds. By spending a lot of time watching things I noticed the icon for solar connection disappearing on the first beep and reappearing on the second. Thus an intermittent connection. Dang it time to check everything out.

So I went through tightening screws at breakers and disconnecting MC4's one by one an trying to see if anything was obvious. On one of the panels MC4 I noticed there was moisture inside the body of the MC4. it was hard to see if this was the issue but out of caution I cut it off and replaced it with a new Staubli brand one. Pulling it apart showed all kinds of corrosion and a badly done factory crimp jump. (This cable was bought way back in my solar journey before I started making my own cables.) Hope this fixes my issue but it does encourage me to replace more of the old MC4's.

Update 7/4/24: Into the second day of the MC4 replacement the annoying beeps from the AIO are gone and output is restored. Does sorta make me wonder how many folks are dealing with wonky MC4's and not realize it?

Mattb4 said:

Had my first failure of a MC4 connector and it was a pain to find. Mostly because symptoms were odd in that most of the time the array produced. But ever now and than it seem to be erratic . I was not sure if the PowMr AIO was to blame . But the last few days I was getting a beep alarm during the day followed by another beep a few seconds later and noticed on the screen that production was zero for a few seconds. By spending a lot of time watching things I noticed the icon for solar connection disappearing on the first beep and reappearing on the second. Thus an intermittent connection. Dang it time to check everything out.

So I went through tightening screws at breakers and disconnecting MC4's one by one an trying to see if anything was obvious. On one of the panels MC4 I noticed there was moisture inside the body of the MC4. it was hard to see if this was the issue but out of caution I cut it off and replaced it with a new Staubli brand one. Pulling it apart showed all kinds of corrosion and a badly done factory crimp jump. (This cable was bought way back in my solar journey before I started making my own cables.) Hope this fixes my issue but it does encourage me to replace more of the old MC4's.

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Sometimes they will get hot or warm to the touch. Every so often I go over all my solar gear with an IR imager looking for hot spots.

Anyone use these?


Crimp free connectors?

And, where is the best place to buy Staubli connector?

Not to mention there are 3 versions now

I bought mine from https://www.ecs-ecart.com/#/ However I do not see a listing for these EVO types.

I have had 100's of MC4 connector failures on my Commercial site. I have been doing significant research on MC4 connectors as some of these have caused some minor grass fires. Some of the interesting things I have found are the actual UL rating and IEC ratings can be different. On my site my DC voltage is 1500 Vdc and I have found MC4 connectors that meet the ULL rating, but not the IEC rating of 1500 V dc have a much higher failure rate. Another factor is having the proper wire stripping tool. If you are cut even one strand, start over. Finally the crimper you use is a major issue. Some MC4's use a barrel while others have bend over tabs. These both require a different crimping tool to get the proper electrical connection. Last but not lease is the human error. You have to make sure your wires are fully seated in the barrel with only 1/16" to 1/8" of extra stripped wire sticking out beyond the crimp. If you get more than that then when you tighten the watertight pieces they may have interference with the stripped wire and cause the connector to not seal up properly.

As far as the right connector and cheap fakes go, I probably have MC4 connectors from 8-10 different sources sitting on my desk and you can definitely see quality differences between all of them and I would definitely not mix and match. The EVO connectors are probably some of the best crimp ones I have seen, but if you're putting in a system with only 500V DC it might be overkill for your project. We just put an order in for 100 no crimp connectors and I look forward to being able to run some testing on them.

Now a lot of contractors are switching to micro inverters and these are only dealing with 50 to 250 VDC. I think even the cheap MC4 connectors would hold up to these voltages if they are assembled correctly. Personally though paying an extra $100 to make sure your home system has good quality connectors seems like a no brainer when this is probably the biggest fire hazard with home solar systems.

Do you use a specific brand of the MC4 on your commercial sites or just something random? Any pattern to the failure?

robbob2112 said:

Do you use a specific brand of the MC4 on your commercial sites or just something random? Any pattern to the failure?

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Staubli EVO 2 connectors are the best I have found currently and my preference, but with over 1 million MC4 connectors used on site sometimes I have to deal with low inventories and get other options. Now their base MC4 connector I have some concerns at the voltage I run at (1500 Vdc) cause the ones that fail most often on my site look like those, but a lot of knock off companies provide the same basic design and look. I can not say the company that built my site used only Staubli MC4 connectors and my request for tech specifications and part numbers have went unanswered. With that said we are moving to only use the EVO connectors. We are looking into their "No Crimp connectors" or the MC4 EVO Ready connectors. It will be some time before I can make a judgement on these though as the biggest gain I could see would be the reduced possibility of human error in their construction.

Another thing to consider is all of my PV wire is 8 AWG wire which most residential systems use 10 AWG or possibly even 12 AWG. The cost difference just isn't worth it on lower voltage/lower current systems. I am currently working on getting some home solar installed, dealing with getting the initial interconnection approved with my utility seems to be a large road block, but since I have lots of 8 AWG wire available I will most likely use 8 AWG in my system. If I even need DC runs, micro inverter technology puts the connections right at the panel making it a very short run. Not sure if I like that though and I might come up with some system that keeps the micro inverters more readily accessible for troubleshooting purposes, just not sure how the wiring management would look coming down the side of my outbuilding is such a system.

I think Stabuli says EVO can mix n match with the old model.
I've got both on couple brands of PV panels and Tigo RSD boxes.

DavidAmon said:

Staubli EVO 2 connectors are the best I have found currently and my preference, but with over 1 million MC4 connectors used on site sometimes I have to deal with low inventories and get other options. Now their base MC4 connector I have some concerns at the voltage I run at (1500 Vdc) cause the ones that fail most often on my site look like those, but a lot of knock off companies provide the same basic design and look. I can not say the company that built my site used only Staubli MC4 connectors and my request for tech specifications and part numbers have went unanswered. With that said we are moving to only use the EVO connectors. We are looking into their "No Crimp connectors" or the MC4 EVO Ready connectors. It will be some time before I can make a judgement on these though as the biggest gain I could see would be the reduced possibility of human error in their construction.

Another thing to consider is all of my PV wire is 8 AWG wire which most residential systems use 10 AWG or possibly even 12 AWG. The cost difference just isn't worth it on lower voltage/lower current systems. I am currently working on getting some home solar installed, dealing with getting the initial interconnection approved with my utility seems to be a large road block, but since I have lots of 8 AWG wire available I will most likely use 8 AWG in my system. If I even need DC runs, micro inverter technology puts the connections right at the panel making it a very short run. Not sure if I like that though and I might come up with some system that keeps the micro inverters more readily accessible for troubleshooting purposes, just not sure how the wiring management would look coming down the side of my outbuilding is such a system.

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I think the general consensus around here is that microinverters are not worth it unless you already have an AC coupled system or serious shading so you have some panels producing when others are making strings a problem. And the problem you noted of having to get up on top of the roof winter or summer to fix or replace one would suck.

In your line of work you might get large enough discount to make it work.

Shawww…and everybody here beat me up recently for saying I didn’t like or use them them… hmmmp…

I will repeat… there are better alternatives …simpler , cheaper and safer…

Woe is the man who stakes his own path in life……

WOW guys that sums it all up @DavidAmon @robbob2112 @Mattb4 - MC4s as a connection concept its crap from day one. The Staubli original was promising at the outset and clearly a precision product but 5x cost of knock offs. Thats where the practice falls over on several counts
a) It opened the door to Cheap Charlie flooding the market with inferior copies which by their poor manufacturing tolerances are not interchangeable (other than making an even more unreliable connections).
b) The basic design requires that considerable skill and attention is need to strip cable and make reliable crimps - in the field. Use of cheap tools, wrong anvils, no proper purpose stripping tool, moments lapse of attention, low grade labour etc all contribute to potential inherent failure and possible fire.
c) Given that there may be 100's even 1000's on site (worse still obscured on a roof under panels), the inspection and maintenance burden must have a considerable financial penalty - especially if a site owner has to use a commercial contractor. (Alarm bells for investors in solar farms)

From my bg this level of unreliability would never be tolerated in the Petrochem Industries

Stand back a moment and review the whole system concept - what a massive scam it all is IMHO and somehow tricked its way into a UL listing (how did it get past their scrutiny - didn't they have enough skill to spot the inherent weakness of the concept and consequences of failure?

I shall ask the boaty crowd if they make much use of these afloat

I talked about this in another thread. Compare the contacts to a simple NEMA 5-15 (15A) plug and socket. Solid conductor plug, and double wiping socket vs wrapped foil plug and socket. Center pin should be solid material with a multi-wiping socket, think euro-plug. Connector housing should be a double insulated (Like the MC4) barrel design with an O-Ring and a threaded locking mechanism like an RF-N or inline miniature cartridge fuse holder. I've been considering creating something, but the startup costs are kind of high.

Sure enough the boaty crew have similar MC4 hell afloat https://www.cruisersforum.com/forums/f14/mc4-connectors-272426.html

So are the regular MC4 connectors from Stabuli a good pick? I can't seem to find the evo-2 version anywhere. Just the base model from what I can tell:

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ksmithaz1 said:

I talked about this in another thread. Compare the contacts to a simple NEMA 5-15 (15A) plug and socket. Solid conductor plug, and double wiping socket vs wrapped foil plug and socket. Center pin should be solid material with a multi-wiping socket, think euro-plug. Connector housing should be a double insulated (Like the MC4) barrel design with an O-Ring and a threaded locking mechanism like an RF-N or inline miniature cartridge fuse holder. I've been considering creating something, but the startup costs are kind of high.

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The old saying KISS If it aint there it cant go wrong.

In short, dont use MC4s on panels. Use solid crimp butt splice cable connections. Think of it - panels are supposed to be in place for decades? If you have to replace one its a significant effort, so cutting and replacing a cable splice (done with proper tools of course) is surely a no brainer. Stick to <48Vdc its inherently safe but uses more cable - safety vs bean counters.

I cant comment on High voltage systems, 400 - 1000V dc systems there must be NEC regs for cable splices - the whole concept scares the hell out of me and I would not go anywhere near such an installation - but Im old school. I far rather see multiple marshalling hubs with field inverters making an ac micro grid. We know how to handle outdoor ac power.

Boron said:

shall ask the boaty crowd if they make much use of these afloat

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I have never see one used on any boat except in a solar use…Ever….. we made real connections that lasted for years…even in a bilge sump under oily ,nasty , salt water…

Although , one should check any connection now and then… nothings perfect…Haa

JRH said:

I have never see one used on any boat except in a solar use…Ever….. we made real connections that lasted for years…even in a bilge sump under oily ,nasty , salt water…

Although , one should check any connection now and then… nothings perfect…Haa

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Ahoy there, what kind of connections were they me hearty? We can learn a lot from ole sea dogs IMHO

as they say Cowboys cant swim.