The customer has 4 x 550 watt Canadian panels, all wired in series.  The installation was completed in August 2023

10 days ago it was noticed that there was 0V input from the panels on the inverter's display

Investigation found that the +ve and -ve MC4 connectors at the -ve end of the string had burnt tubes.  Replacing both made the string produce 180 volts and 8.4 amps.

The damaged MC4 connectors were securely joined together and had been cable-tied to the rail under the panels.  These were the MC4s that came attached to the panels on a flying lead

Most likely because the mating connectors weren't compatible, or badly crimped. This is the biggest risk with poor installations. Ideally all mating connectors should be of the same manufacturer and same series. Rule of thumb is that if it has a red oring, it's not genuine Staubli (most likely what the Canadian solar panels came with) - if it has a black oring it might be. It's worth paying the exorbitant prices for Staubli connectors and proper crimping tools if it means your house won't burn down.

3 hours ago, chrisc said:

These were the MC4s that came attached to the panels on a flying lead

Do you mean they came pre-installed on the solar panels?

7 hours ago, chrisc said:

The customer has 4 x 550 watt Canadian panels, all wired in series.  The installation was completed in August 2023

10 days ago it was noticed that there was 0V input from the panels on the inverter's display

Investigation found that the +ve and -ve MC4 connectors at the -ve end of the string had burnt tubes.  Replacing both made the string produce 180 volts and 8.4 amps.

The damaged MC4 connectors were securely joined together and had been cable-tied to the rail under the panels.  These were the MC4s that came attached to the panels on a flying lead

That is the reason i use a 1000v 32 amp dc isolator to test ISC( short the string out in good sunshine) take a current reading compare to specs then leave for 1 hour and the guys feel each mc 4 connetor for bad seating and incorrect crimp connections.( heat) Never use the mc 4 connectors at the end to do this test as you will destroy the connector when you disconnect( huge arc).Below dc isolator i use for this test with leads and mc4 connectors attached to the contacts. All this is done before connecting the strings to the dc combiner.

11 hours ago, chrisc said:

The damaged MC4 connectors were securely joined together and had been cable-tied to the rail under the panels.  These were the MC4s that came attached to the panels on a flying lead

Most of the times the crimp itself is good, but the internal pins of the MC4 are not in the proper position (there must be audible click sound for each connector during it's completion, male and female..and then a third click as you plug them together.).

See thread here: 

 

Speaking of incompatibility, the best is to buy a bag of MC4S, cut the connectors from the starting and ending pigtail of a PV string and crimp the same type of MC4 to that pigtail and to the "downlink" cable too.

BTW: burnt MC4s are pretty common. A coleague of mine does repairs and checkups of large industrial PV parks and saw hundreds of burnt MC4 connectors already. Some of them were even smoking and melting just in front of him. 

Edited January 11, 20251 yr by Youda

If I had to bet, would be on connectors was dirty when connected It will make them heat. In a sunny day could be enough to burn.

Installers and electricians that are solar operators take a moment to read this blog and discover some reasons for mc4 connector failures it is all in the details of a solar array installation.

https://www.solarquotes.com.au/blog/solar-panel-mc4-plugs-failure/#:~:text=The litany of failures you,become the default industry standard.

This is something that manufacturers irritate me with.

MC4 is not only a connector type, but a standard, yet some manufacturers think they can deviate from the standard and make subtle changes to the design, causing brands to be incompatible with each other due to risk of poor contact, and therefore heat, melting and possibly fire.

Imagine the standard South African type M plug or for UK users, the type G plug. Now imagine every manufacturer of plugs and sockets, of which there are many, decide they are going to vary their pin design in length, or thickness by 0.1 - 0.2mm. The amount of havoc there would be in the market, as well as the fines they'd get for this.
The same should be applied to the solar industry.

This is the set standard, you abide by it, if you don't, you get a hefty fine and held liable for damages incurred.

You would expect a premium brand PV panel to use quality MC4 connectors.  The inner metal parts overlap 8mm as far as I can measure and in full sun deliver about 35 volts and 12 amps.  

Is that thin tube adequate to handle that current?  

230 volt mains plugs have far more substantial and robust

I spoke to the supplier.  He said straight away that I must have not connected them properly as he had never heard of such "nonsense" since he started his business

The connectors were tucked under the edge of the panel and attached with a cable-tie

On 2025/01/11 at 11:21 AM, Kalahari Meerkat said:

Do you mean they came pre-installed on the solar panels?

Yes

27 minutes ago, chrisc said:

You would expect a premium brand PV panel to use quality MC4 connectors.  The inner metal parts overlap 8mm as far as I can measure and in full sun deliver about 35 volts and 12 amps.

They are pretty decent. Most of the issues are happening at the start/end of the strings, where you connect panel to the "downlink" cable....and therefore MC4s from different vendors are mating.

 

29 minutes ago, chrisc said:

Is that thin tube adequate to handle that current? 

Yes, it is.

 

30 minutes ago, chrisc said:

230 volt mains plugs have far more substantial and robust

Not really. They look like, but try to run 32Amps thru 230V AC plug for 8hrs in a row and you will see. Not to mention that 230V AC plugs are not IP68 rated. MC4s are.

31 minutes ago, chrisc said:

I spoke to the supplier.  He said straight away that I must have not connected them properly as he had never heard of such "nonsense" since he started his business

Oh yes....:

 

 

 

 

 

14 hours ago, chrisc said:

You would expect a premium brand PV panel to use quality MC4 connectors.  The inner metal parts overlap 8mm as far as I can measure and in full sun deliver about 35 volts and 12 amps.

The Staubli connectors that come with the panels are about as premium as they get, they stuff that is usually mated to it is usually far from it.

The connectors have a completely different structure than what you get in a typical wall plug - look inside the female and you will see they have a number of spiral or straight contacts made from plated spring material. This arrangement ensures much better contact than the (usually 2) contacts in an AC socket.

22 hours ago, Bl4d3 said:

MC4 is not only a connector type, but a standard,

I'm pretty sure that's not true, and also the source of many of the problems.

It was a quite an inexpensive repair however.  2 x MC4 connectors for R60,00 and 45 mins on site

Edited January 14, 20251 yr by chrisc

On 2025/01/13 at 7:55 AM, P1000 said:

The Staubli connectors that come with the panels are about as premium as they get, they stuff that is usually mated to it is usually far from it.

The connectors have a completely different structure than what you get in a typical wall plug - look inside the female and you will see they have a number of spiral or straight contacts made from plated spring material. This arrangement ensures much better contact than the (usually 2) contacts in an AC socket.

I'm pretty sure that's not true, and also the source of many of the problems.

You are correct.

After doing some more reading, Stäubli invented the MC4 connector however they refuse to license the standard to others, which has in turn caused many to start copying, which is where the problem comes in.