Damp inside solar MC4 electrical connectors

Has anyone else thought - "my solar panels should not have been installed in the rain / damp weather"?

My solar panel installer company claims it's OK to install on the roof in all weathers, all year. Rain did get inside my connectors, and the roofer plugged the connectors together anyway. The damp will never escape the IP68 (= waterproof) connector, and so will corrode the (tinned) electrical contacts within.

It seems a fact that the corrosion will stop the system working within a year to two, and most certainly within the 10/25-year guarantee.

What do other engineers think? And did you complain?

If enough IET electrical engineers who had solar installed all agree, then finally the solar installation industry will have to listen.

Cheers, Adrian.

  • Manufacturers will tell you their connectors are only weatherproof when they have been assembled correctly (torqued up etc) and mated with a matching connector per instructions. For example, Staubli MC4 Evo-2 is IP68 when mated, but only IP2X unmated.

    I have seen the after-effects of "MC4s" (from various manufacturers) installed in poor conditions without due care, or where damp is otherwise is allowed in, and from a large enough batch some will indeed fail. It is an issue the utility-scale solar industry is aware of at least. Whether domestic installers stop to think about it I couldn't say; as with everything in domestics I suspect it varies.

    This does not necessarily mean that installs should never take place in poor weather, but that when it is, measures should be taken to keep the connectors dry until they're mated and checked. Indeed on larger constructions measures may need to be taken even in dry weather if it is likely to rain (or get dusty) twixt making up connectors and mating them. Fortunately the design of a made-off connector work in one's favour such that external damp surfaces can be safely wiped dry while the risk of water getting directly insde is more from being left in pools of water, on the ground or clipped in running streams, rather than an errant rain-drop under a light mist... but I would not (and do not) accept wet connectors being mated and am absolutely not above requiring cables to be reterminated where there is a risk of damp.

    End caps are available if they are to be left exposed for a period, but less high-tech solutions are normally adequate for temporary situations.

    Meanwhile if it's really hammering it down, is that the best time to be sat on a roof working with live 1000Vdc, from an EAWR perspective? Note again that until they're mated the connectors are only IP2X, and there may well be no means of isolation.

    Hope that helps

  • The damp will never escape the IP68 (= waterproof)

    IP68 isn't exactly hermetically sealed - as some of us have found to our cost apparently water tight enclosures can often end up with moisture inside them - often a combination of condensation (the standards make no mention of keeping gaseous water vapour out) and pressure changes as temperature cycles (typically boxes exposed to direct sunlight during the day, then freezing temperatures overnight). Those that are serious end up with pressure equalization/breather caps in addition to all the seals.  So I suspect the same might be true of trying to keep water in - after a few months on a roof, being baked in the sun (if indirectly if behind a panel) - some will slowly, molecule by molecule, find its way out, so the situation might not be quite as bad as envisaged.

       - Andy.

  • Thanks @Jam, all the MC4 connectors have now been replaced, together with the attached PV panels and optimisers! It really helped to know where I stood, from your excellent advice.

    The solar company eventually agreed to bag every new MC4 half-connector individually, in case of rain (not onerous), until just before mating the connectors. However each worker (roofer, roofing manager, & electrician) that arrived one at a time to do the replacement, still argued against it!

    The solar installers have proven to be a really honourable company, IMHO. This year (2023) they have the council contracts for Solar Together Suffolk, Norfolk, and Bedfordshire.

  • There's a lot of deafness in the Solar Energy jungle, a very fertile ground for misinformation and hazardous Cheap Charlie installation.  We are simply not up to speed compared to our Cousins across the pond and down under.

    Adrian as for your concern, people mostly forget that solar energy is dc, so any volts applied (even at very low level) will promote galvanic corrosion immediately  - especially worse in marine or coastal locations.

    Personally I hate the MC4 system. No doubt it was sound enough when launched by the originator German Staubli gmbh.  However there are many different makers on the market and Installers can source products as little as 1/5th of the cost of the genuine article (ca £5 ea).  Apart from manufacturing quality, these look-alike connectors are not necessarily interchangeable (like our ubiquitous 3 pin uk plug).  Current an be as much as 50 Adc so when they dont make proper contact, incipient arcing can occur and over time develop into a full arc flash breakdown.  Numerous Youtube videos out there to demonstrate the consequences.

    Ask for what to do - IMHO I would insist on long tails fitted to panels so there are no MC4s on the Roof (if its not there it can't go wrong).  Said tails can be routed up to the ridge and brought down into an attic void and a convenient large Marshalling cabinet.  BTW a cat walk grid along the ridge is very convenient and barely visible from ground.  I would strongly warn against any inclination to use Cheap Charlie panels as YouTube will show the effect of fires from internal short circuits.

    As I have spent a year researching the topic I could ramble on for pages, so here I simple opine your question

  • While I don't disagree with the sentiment I would note that unless you are ordering in enough bulk to make a panel manufacturer take notice (that's MW) you aren't going to get tails long enough to run all the way to a marshalling cabinet. Therefore joints of some kind are unavoidable.

    Given that the reason for taking action is sufficently high risk of faulty connectors, there's then a tradeoff between reducing the risk of water ingress into a badly made connection on top of the (comparatively fire-resistant) tiles and an electrical arcing fault in the loft space which can't be easily isolated. And, depending on the site, there may or may not be an increased risk of cable damage in the loft space.

    I would also suggest that terminating onto the DC marshalling box correctly would require if anything more skill and care, and careful product selection, than the MC4s.

    And with that number of roof penetrations there's also a greatly increased risk of a faulty install leading to water ingress.

    I would suggest that a better approach would be to drive down the risk of faulty connectors by ensuring that they are made only by competent personnel with the correct tools under the right conditions, to heed the guidance from the IET CoP regarding connectors from different manufacturers, and to mount the connectors suitably e.g. so they're supported and not left in a pool of water. And as always avoid low / suspect quality goods.

    That is not to say that I don't have dreams of doing similar with my own personal installation when I finally get to it, but that would be a bespoke arrangement for convenience for measuring and tinkering with stringing, since I have a professional stake in the sphere, and not something I would recommend to others.

  • I do not know how well the "Cheap Charlie" as rob so colourfully puts it installers consider their wiring layout for EMC but as the things become more prevalent, so will the problems, and there are already many reported issues....

    So, if one is advising folk on how to layout tails I would also point out that  poor layout creates an accidental antenna that can greatly worsen the re-radiation of  inverter frequency related hash. In a perfect world there would be filtering on the DC side, but of course 'value engineering' means this is absent of minimal, but it costs nothing to point out things like it is very bad form to organise panels so they create an accidental loop of large area, and much better if the 'flow' and 'return' cables of any string are arranged so that cancelling currents are  run within a few cm of each other, (ideally as twisted pair but I cannot see that happening), and proper earthing of on-roof metalwork.


  • Hmm Mike, I havent heard of that concept - radiating Inverter frequencies thru panel cables - hasnt appeared on any forums particularly across the pond.  They are so far ahead of us (as are the Ozzies)

    As for making tails, I suggest that a commercial professional crimped butt joint which can be filled with silicone grease before closure.  This needs to be done with a proprietary toolkit and its expensive ca £100.  I have seen Cheap Charlie crimping systems and these are nasty made even worse by fake thin sheet lugs that couldnt possibly make a "Cold Weld" joint.

    I need to do some more research on this on other forums as I cant quote a suitable professional system just now

    more work needed


  • I suggest you search for EMC problems from solar installations - there are certainly plenty of reported examples where a poor installation obliterates radio reception neighbours and in some cases for miles around.

    Problems in the USA https://www.youtube.com/watch?v=SusTlmeEvqc


    In the UK we are less flightly and the RSGB is taking a measured look into it https://rsgb.org/main/technical/emc/solar-pv-panels/

    In the mean time this is their advice


    The American Radio Relay League offer the following https://www.arrl.org/solar

    And in Oz... https://qrm.guru/502-2/

    I'm sure there are more.


  • That's very interesting, thank you for posting and one for the "library".

    (Granted some items in the baseline fail to meet what the IET CoP requires over here (albeit it might well be what is done in many domestic installs), and one might suggest module-level optimisers weren't perhaps the best choice for that customer... while the multiple windings around a core might raise questions of grouping vs cable rating)

    I would be very interested to see how an installation that actually follows the CoP performs under this level of scrutiny as a mid-level comparison.

    [Edited for formatting]

  • Hi Jam

    I browsed the RSGB article as posted, its very well presented.  I f take a cursory look it seems one should avaoid creating a loop with the individual cables stringing around panels and should try to make parallel cable runs.  The interesting thing is the simple suggestion of twisting two cables +ve and -ve in as far as one can with a 6mm solar cable - quite stiff.  This should help reduce HF radiation.  The use of ferrite rings etc towards the inverter input is new to me as is twisting cables, but it seems some science is needed to formulate a practical guide for installers.