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MCB for Solis Inverter and Grid Standard to use

  • 04-06-2022 1:20pm
    Registered Users Posts: 301 ✭✭

    Hi all

    Couple of Q's to those with Solis Inverters installed.

    1. What size MCB have you connecting the inverter? I currently have a 16 amp on a 5kw inverter and on very sunny days recently it has tripped a couple of times at peak production. I'm wondering if 20amp is more common?
    2. Currently my grid standard is set to G99 but I'm wondering if EN50549IE is the one it should be set to.


  • Moderators, Education Moderators, Home & Garden Moderators Posts: 7,915 Mod ✭✭✭✭Jonathan

    1) The MCB is there to protect the cable, not the device. Do not increase the MCB without first checking the cable rating. I have a 32A MCB on 6mm2. Decent chance that your inverter could be run with only 2.5mm2 if a 16A MCB was fitted.

    2) Last time I checked Solis don't have EN50549IE available as an option, only the generic EN50549L option. You need to enter the Irish specific parameters as custom options. Solis said it was coming in a future firmware.

  • Registered Users Posts: 301 ✭✭E30M3

    Thanks Jonathan

    I actually have EN50549IE available as an option so that was why I was querying. Installed about 18 months so it may not have been available for the installer then as I am set to G99.

  • Moderators, Education Moderators, Home & Garden Moderators Posts: 7,915 Mod ✭✭✭✭Jonathan

    Ooh, thanks for that. Must climb up to the attic to have a look. Maybe it was added in 3A0029.

  • Registered Users Posts: 63,556 ✭✭✭✭unkel

    It's very simple, P=V*I

    240V * 16A = 3800W

    Your inverter is 5000W so that explains that on a sunny day when your PV generates close to that (so way over the MCB rating), it will trip. Makes you wonder who installed that, probably not a proper sparks? Or did you significantly upgrade your PV system yourself after the initial setup was done (with the 16A MCB)?

  • Registered Users Posts: 1,660 ✭✭✭Deagol

    Err... that's not correct really. It depends on how many panels are fitted not the size of the inverter.... but in the case he has panels then yeah, not surprising the MCB is tripping.

    OP - Don't change the MCB unless you completely understand what you're doing. If you oversize the MCB for the cabling - both cabling from the inverter and in the case you might have an aux or remote Consumer unit - the cabling that goes back to the main CU, you could very easily cause a fire. Strongly recommend you get an electrician in to look at it if you're not 100% sure.

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  • Registered Users Posts: 63,556 ✭✭✭✭unkel

    Not correct? It's obviously tripping because his panels (via his inverter) generate well more than 3.8kW. Or do you have another likely explanation? 😂

  • Registered Users Posts: 1,660 ✭✭✭Deagol

    No need to be rude...

    There could be a number of other explanations - there could be a fault in the system somewhere etc. You've jumped to a conclusion based on very little information. Chances are you're correct but can be dangerous to start advising someone on the basis of a rushed conclusion.

    I'm wondering why someone, assuming the system was fitted by and commissioned by a qualified electrician as required legally, would fit a MCB that is smaller than the inverter / solar system can provide. So I'm advising the OP to be cautious.

    But here, I'm not getting into a dick swinging competition with you, from other threads I've noticed you like to win arguments for no other reason than you think you're always right. I'll withdraw from this thread - OP, if you want proper advise feel free to PM me any time and I'll try and help.

  • Registered Users Posts: 63,556 ✭✭✭✭unkel

    No need to be so sensitive / defensive, @Deagol

    You told me I was wrong. Quite rude that, while you knew full well that I was most likely right. Also no need to start talking about swinging dicks, not something most people here are interested in and nothing much to do with what this forum is about

    That said, It's good that you agree with my point questioning what way and by who the system was installed. It leaves a lot of questions unanswered.

  • Registered Users Posts: 301 ✭✭E30M3

    For Clarification

    I have nothing like a 3800W output limit. I have 16 350 w panels on a 5000w Solis Inverter and regularly pull well over 5000w issue free as the chart from a recent day shows.

    -Makes you wonder who installed that, probably not a proper sparks? 

    My system was grant aided and installed by probably the most recommended and discussed firm on each of the quote threads we have had to date on this forum.

     -Or did you significantly upgrade your PV system yourself after the initial setup was done (with the 16A MCB)?

    I replaced 2 Pylontech batteries with a 16 CALB / Seplos setup over the last few months. This is the only change made.

    Lots of folks here have way more experience and knowledge that I will ever have and that is why I ask questions and hopefully along the way other people will benefit from the information posted in response.

    I haven't see any discussion or suggestion that a DIY battery may introduce an MCB trip issue but I think that is what is happening to me. My working suspicion based on my observations is the following;

    -No issue with MCB when battery is charging irrespective of the panel/inverter output.

    -No issue with MCB when battery is not online irrespective of the panel/inverter output.

    -Issue with MCB experienced when peak panel/inverter output happens after the BMS has hit 100% and is now trickle discharging to get back down to 96%. This small additional load added to the panel/inverter output is what I suspect is causing my issue but that is only based on observation. This small discharge dictated by the Seplos BMS is not within the inverters control and I may be on the margin anyway with the 16a MCB.

    -No Trip issue that I recall in the 18 months prior to swapping the battery. I hadn't considered the size of the MCB etc so thats why I'm now suspecting the battery swap and considering approaches.

    I would only swap the MCB for a larger one if my theory proves correct but because I haven't seen anyone else with this issue I wanted to see what is the MCB size they are using. If swapping it will be an electrician doing it but I wanted to ground my approach first.

  • Moderators, Education Moderators, Home & Garden Moderators Posts: 7,915 Mod ✭✭✭✭Jonathan

    Can you both be civil to each other please. You are both good contributors to the forum, and I'd rather not have to get into ban territory if I can avoid it.

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  • Moderators, Education Moderators, Home & Garden Moderators Posts: 7,915 Mod ✭✭✭✭Jonathan

    Have a look at the trip curve for a B type MCB:

    You'll see that it doesn't trip immediately at 16.001A, but rather the trip time is based on the amount of current.

    You can see from the graph that a B type MCB can sustain approximately 1.5 times it's rated current for 500 seconds before it trips. In your situation, that means 1.5*16A=24A*230V=5,520W for 500s (8mins 20secs) before it trips. Obviously in a short circuit situation, the current is high enough that the trip time will appear instantaneous.

    What orientation do your panels face? I am assuming they are not all south facin if this has not been a problem for you before you got your DIY battery? As outlined above, it would need to see 3.68+kW from your panels for a sustained period to trip.

    The DIY battery changes things however... The Pylontechs are limited to 25A each, so for two of them that means 50A*51.2V=2.56kW => well below 16A@230V. With the DIY cells, you can charge/discharge at 100A on the Solis 5G, so you can see now how can trip the 16A MCB fairly quickly.

  • Registered Users Posts: 301 ✭✭E30M3

    Thank you for the info Jonathan. My Solis is limited to a discharge of 62.5 A rather than 100 A is what I see. However I have no issue where the Battery is actively discharging but only when the trickle discharge to reduce the SOC by the BMS is happening at the same time as Peak power from the Panels.

    12 Panels East and 4 West is my orientation. Really only see peak power this time of the year with the sun directly overhead.

    For context the MCB has tripped less than 10 times so far and as I say all on peak panel points when the battery via the bms is trickle discharging.

  • Registered Users Posts: 791 ✭✭✭reklamos

    @E30M3 there must be a reason why installer put 16Amp MCB. I would sugest to ask them as it does not make sense to have 16Amp MCB when your inverter is rated at 5kW on AC side(max is +10%). So on a good day when batteries are full and you start exporting or even if you start using a lot, sooner or leter it will trip. I have 5kW Solis and MCB is 25Amp which is 6kW. It has never tripped in 3 years and there were plenty times when AC on inverter side was pushing just below 5.5kW. I noticed from my logging that as soon as it goes above 5.5kW it starts suplementing from the grid even when there is plenty solar and battery available but that is expected.

  • Registered Users Posts: 9,761 ✭✭✭Effects

    If the cable was a 2.5, wouldn't a 20A MCB be suitable? Mine is ran in 2.5 with a 20A RCBO at the fuse board.

  • Registered Users Posts: 9,761 ✭✭✭Effects

    What size cable is running from your inverter to fuse board?

  • Moderators, Education Moderators, Home & Garden Moderators Posts: 7,915 Mod ✭✭✭✭Jonathan

    All depends on the temperature rating of the cable and how it is run. You need to derate the cable if it is in a wall with insulation vs clipped direct etc.

  • Registered Users Posts: 9,761 ✭✭✭Effects

    Ah yeah, of course. I guess I was only thinking of my route, which is up from a stud wall and across a ceiling void, and only a few metres.

    Been meaning to get the new rule book since it came out!

    I'm trying to plan a new cable run myself, which might involve running steel conduit down a south facing wall. Overheating in summer a consideration alright.

  • Registered Users Posts: 791 ✭✭✭reklamos

    Do not see any markings on the exposed part of the cable but judging by diameter I would say it is 4-6mm2.

  • Registered Users Posts: 9,761 ✭✭✭Effects

    Ah ok. Good that it could be 4mm2 or higher. My electrician basically did the bare minimum on my house. Even placed the panels in permanent shade until I kicked up a fuss about it.

  • Registered Users Posts: 301 ✭✭E30M3

    Thanks to all the helpful posts to date.

    I contacted the installer and outlined my issue and he felt the 16A MCB was a mistake and too small for my setup.

    I will arrange to swap for a 20A.

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  • Registered Users Posts: 9,761 ✭✭✭Effects

    Just to confirm. Is it an MCB or RCBO that he installed? I thought that you needed to have an RCBO so it would disconnect both live and neutral in the event of a fault.

  • Registered Users Posts: 301 ✭✭E30M3

    MCB was tripping. This did not trip the RCBO for the consumer unit. 16 A MCB replaced with 20A MCB

  • Registered Users Posts: 9,761 ✭✭✭Effects

    Just checked my board, and I've a 20amp RCBO for my panels, so they don't affect the general RCD for the other circuits. I think that was the regs back when mine was installed in 2017 but I'd need to double check.