Sofar ME3000SP neutral earth bond failure?

[Joseph_Martin]

Hi,

I've just had a periodic inspection of our electrical installation, as it's ten years since our home was first built (I'm in the UK where we're supposed to get inspections done every ten years). Unfortunately the electrician has failed our installation because of a serious safety defect with the Sofar ME3000SP. We have six Pylontech batteries connected to the Sofar ME3000SP inverter/charger and the system has worked very well for about three years now (and was still working well until the electrician disconnected it as being unsafe). I've tried to contact the installer we used but it seems they are no longer in business. I also tried to contact Sofar in China who were simply dismissive and extremely unhelpful. I've not been able to find any UK agent for Sofar, only re-sellers.

The system was installed so that in grid mode it charges the batteries from excess power from our solar system, or charges them over night during the off-peak cheap rate period. The batteries then run most of the power for the house during the day, when grid electricity is more expensive. Up until the time it was disconnected it has always worked very well and massively reduced our bills. In addition to this, the installer also wired the emergency power supply output of the unit to a changeover contactor and a small consumer unit that runs the lighting circuit plus a single socket circuit that runs our internet stuff plus the TV. This has also always worked very well, as we live in an area that gets a few power cuts each winter and having power back on to the lights etc a couple of seconds after the grid goes down is very useful.

Talking to the electrician he has declared it unsafe to use because of the emergency power circuit. On the report he has stated that, when he tested it he found that there was no neutral to protective earth bond when the system was running in EPS mode. He's also noted that he measured an unsafe voltage between neutral and protective earth and this is given as the reason for disconnecting the system as being unsafe to use. His report does also mention that the neutral to protective earth fault is not present when the system is running normally (i.e. when there isn't a power cut). I've done lots of research over the past few days and found a great deal of useful information about neutral to earth bonding relays, along with some heated debates about whether or not these are needed, safe, etc.

Our electrical installation has a TT earthing system, with an earth rod by the meter cabinet and an RCD and fuse unit on the cable that feeds the house (the house is about 10m away from the meter cabinet and fed via a length of hefty armoured cable). I believe that the Sofar ME3000SP is like several other Chinese inverter/chargers in that it does not have an internal neutral/earth relay. I tried to get Sofar to answer the question as to whether one could be wired externally (as suggested for some other inverters with this same issue) but they just told me that the ME3000SP is an old product and they do not support it now. I've talked with the electrician and he has said that it would be easy to add an additional contact block to the existing changeover contactor, wired so that the EPS neutral was switched to earth when the contactor energised. This sounds great, as he's said it's a very quick and easy job and the part needed isn't that expensive. However, he doesn't want to risk doing it unless he knows for sure it isn't going to cause damage.

So, my question is, does anyone know for sure if it is safe to just add another switch to the existing changeover contactor that links the EPS neutral to earth when in off-grid mode, please?

 

[SeaGal]

Welcome!

Firstly, I'm not a sparky, so this is only my opinion from my own Solis-based system, also with a TT earthing arrangement.

I'm puzzled by the 10 year inspection you mention. I understood that was only mandatory to have a EICR if you are a landlord renting property and, otherwise, discretional. Either way, it is good that an issue has been found for you and your family's safety, but still puzzled by your concern about your inverter being disconnected.

As it was found safe when used in grid-tied mode, then, if it were my installation, I would be happy to continue using it in that mode alone and simply disconnect the backup supply until the issue is fixed.

With regard to the backup supply, it sounds as though the Sofar is similar to the Solis in that during a power outage, i.e. when the AC backup port is powered by solar/battery there is no PE provided. Hence, IMHO, you should have a separate earthing (TT) point on the backup supply which is on a separate circuit to your main CU.

 

[Joseph_Martin]

Thanks for the words of welcome!

I had the inspection done because there was a sticker on the consumer unit giving the date that the next inspection was due, presumably put there when the house was built. Looks official to me and makes it clear that this inspection should be done on or before the date given (which was a couple of weeks ago now).

I agree with the logic that the system should be safe to use in normal, grid, mode, but the electrician was adamant that he wasn't prepared to leave it connected as, in his words "if there is a power cut then your installation is very dangerous". He's completely disconnected the unit and put a locked seal on the RCBO that supplies it, so it cannot be turned on until repaired.

There isn't any problem with the earth, that all tested out OK. There is always a working protective earth at all the outlets, including those from the second emergency power consumer unit. The electrician has given the impedance values he measured at every earth and says they are all well within the requirements.

The problem is that the neutral always needs to be connected to earth, whether in grid mode or in emergency power mode. As explained to me, this is done via the incoming grid supply when running from the grid, as that has the neutral connected to the earth at the local transformer. When the Sofar switches to emergency power mode it operates a changeover contactor (the wiring diagram for this is in the Sofar manual, I've cut and pasted it below). This changeover contactor disconnects the grid supply from the second consumer unit and connects the Sofar EPS output to it instead. This is where the problem arises, as by doing this the required neutral to earth connection gets broken (because that's normally done via the incoming grid supply). The consequence of this is that the neutral voltage rises to over 100V above the earth, which the electrician considers to be dangerously unsafe (and I have to agree with him, it does seem unsafe). The electrician also mentioned that there was another risk from circuit protective devices not operating correctly because of this, and has given that as another reason to disconnect the system for safety reasons.

One thing I have read about a fair bit when trying to understand this problem is that some battery inverters can have this problem fixed by adding an external neutral to earth contactor. There are a lot of references to this being the fix for Sunsynk and Deye units, for example. In all my searching I've not found any reference to someone adding such a neutral to earth relay or contactor to a Sofar inverter, though. All Sofar are saying is that I must throw away the ME3000SP (which isn't even three years old) as it is now obsolete and replace it with their newer HYD3680 unit, which they say does make this neutral to earth connection (although frankly I don't trust them to be telling the truth now).

 

[SeaGal]

The consequence of this is that the neutral voltage rises to over 100V above the earth, which the electrician considers to be dangerously unsafe (and I have to agree with him, it does seem unsafe). The electrician also mentioned that there was another risk from circuit protective devices not operating correctly because of this, and has given that as another reason to disconnect the system for safety reasons.

That makes sense to me - domestic equipment will be fused on the live wire only and, if not double insulated could have a fault condition causing high voltage on the chassis, which is not safe. If you have an RCD / RCBO on the back-up output then that should trip as soon as there is an imbalance between current on the L and N wires, but best not to rely on that for primary safety. I can't think of any reason not to N-E bond the backup supply external to the inverter in that situation, but as I mentioned before, I'm not a sparky - hopefully someone with more qualifications in that area will chip in soon.

 

[Joseph_Martin]

That makes sense to me - domestic equipment will be fused on the live wire only and, if not double insulated could have a fault condition causing high voltage on the chassis, which is not safe. If you have an RCD / RCBO on the back-up output then that should trip as soon as there is an imbalance between current on the L and N wires, but best not to rely on that for primary safety. I can't think of any reason not to N-E bond the backup supply external to the inverter in that situation, but as I mentioned before, I'm not a sparky - hopefully someone with more qualifications in that area will chip in soon.

Many thanks, it's nice to know that I'm not going bonkers by thinking this should be a fairly easy thing to put right. Be great if Sofar had been more cooperative, though. There's a lesson to be learned there about price and quality of service, I'm sure. No doubt if I'd bought something top-of-the range, like Victron, they would be more forthcoming about making things safe.

Although the risk seems very real now I know about it, we have been running the system for nearly three years now and it's kept us going through at least half a dozen power cuts. We had another power cut for about 4 hours yesterday and it was a real nuisance not having lights, the internet or the TV!

One positive thing to come out of this is that I now know just about enough about electrical installations to be dangerous, having spent a couple of weeks trying to bottom out fixes for this problem. I can't help but wonder quite how many other system like this have been installed with no neutral to earth bonding relay. I bet there are hundreds, as the installer we used was very busy installing these systems; we had to wait several weeks to get a slot. No doubt they will all be like ours, with just a floating supply when in emergency power mode. Mind you, from what I can gather the majority of small portable generators work like this too, which does make me wonder whether the real risk is quite as scary as our electrician has made out.

 

[SeaGal]

I can't help but wonder quite how many other system like this have been installed with no neutral to earth bonding relay. I bet there are hundreds, as the installer we used was very busy installing these systems; we had to wait several weeks to get a slot. No doubt they will all be like ours, with just a floating supply when in emergency power mode. Mind you, from what I can gather the majority of small portable generators work like this too, which does make me wonder whether the real risk is quite as scary as our electrician has made out.

I'm sure there are lots. I do agree though, the risk is there, but would have to be a sequence of events for it to happen - hence still best to mitigate as far as possible.

I had a similar discussion on here last summer about that very issue, and got some very good feedback from @mikefitz - see my posting here and his reply.

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[Joseph_Martin]

Many thanks again, that link you gave was the clearest explanation I've seen of the true problem. I just wish I could find out if the Sofar ME3000SP would be tolerant of having the Load neutral linked to earth in EPS mode. I'm 90% sure it would be fine, but that 10% might be something that causes a large BANG!

 

[SeaGal]

YW. If you can't sleep tonight, just do a search on here for "neutral earth" posted by MikeFitz and you'll find plenty of good stuff to read

With my electronic engineering hat on, I can't think of any reason why bonding the floating output of the inverter to ground only when operating in back up mode would cause an issue, especially as, like us, you have TT earthing - will mull that over.

Do keep us updated.

 

[Joseph_Martin]

YW. If you can't sleep tonight, just do a search on here for "neutral earth" posted by MikeFitz and you'll find plenty of good stuff to read

With my electronic engineering hat on, I can't think of any reason why bonding the floating output of the inverter to ground only when operating in back up mode would cause an issue, especially as, like us, you have TT earthing - will mull that over.

Do keep us updated.

Many thanks again, much appreciated! One gem I found from that search was the advice to test whether something bad might happen from making a neutral to earth link on the EPS side by using a lamp to check whether any appreciable current flows via that link. The idea being that if the lamp lights then that indicates something bad may happen if a neutral-earth contact is added. I'll have to have a dig around tomorrow and see if I have any old incandescent lamps left and then have a go at testing this.

I've had a look at the changeover contactor that the installer fitted and can see exactly what the electrician meant when he mentioned adding another contact module. The contactor is a Schneider Electric Acti 9 iCT (this model: https://www.se.com/uk/en/product/A9...r/??range=7563-ict&selectedNodeId=12143453995) that has two NO contacts and two NC contacts, but there is an add-on contact block available (this one: https://www.se.com/uk/en/product/A9C15914/remote-indication-auxiliary-acti9-iacts-1-no-+-1-nc/) that clips to the side and gives additional contacts that operate at the same time as the contactor. Looks like adding one of these will give the option to link the critical load supply neutral to earth whenever the grid goes down, which would seem to be exactly what's needed. The Sofar wiring diagram would then look like this, if this makes sense:

 

[mikefitz]

If you have an RCD / RCBO on the back-up output then that should trip as soon as there is an imbalance between current on the L and N wire

No , not without the neutral to earth bond, that's why the electrician was concerned enough to disable the system.

easy to add an additional contact block to the existing changeover contactor, wired so that the EPS neutral was switched to earth when the contactor energised.

I suggest you get your electrician to make this modification. When in stand alone mode the inverter should, ( if designed correctly for the UK), make the neutral to PE bond. This is how Victron implement this,


If you inverter was designed with quality components there should be a low risk of damage.

 

[Joseph_Martin]

No , not without the neutral to earth bond, that's why the electrician was concerned enough to disable the system.


I suggest you get your electrician to make this modification. When in stand alone mode the inverter should, ( if designed correctly for the UK), make the neutral to PE bond. This is how Victron implement this,

View attachment 191075
If you inverter was designed with quality components there should be a low risk of damage.

Very many thanks for chipping in, Mike, it's much appreciated. I've been going doolally with all the conflicting "advice" I've been given, especially that from Sofar in China, who seemed intent on getting me to buy their latest model and bin the 3 year old ME3000SP (that has worked very well since it was first installed).

The ME3000SP has UK approval, I have the chit stating this from the original installer, although quite how they managed to sign everything off when the installation was so potentially iffy I do not know. They've seemingly gone bust now, so perhaps that was their just reward for doing dodgy work. Worrying that there are most likely other installations like ours, though. Ironically, the reason we chose this particular installer was because they said they were specialists in providing back up supply systems for those like us, living out in the sticks with grid power that goes down regularly in bad weather.

I've called the electrician and he's agreed to do the test lamp check and if that's OK fit the additional contact block, do the safety testing again and hopefully get the system back up and running. He reckons it's probably a pretty quick job, so he's going to try and fit it in between other jobs when he's in the area, which is great. Not likely to be that expensive, either, which is even better news.

 

[kommando]

UK approval ie G98/G99 is only for the DNO, ie that it shuts off in a controlled manner and turns back on in a controlled manner to protect the Grid. What it does as long as its not grid connected does not enter the test. If you look at the tests for this approval the earth is not part of the test even when grid connected, the DNO does not care about you being electrocuted only the linesmen and the Grid function.

https://www.ena-eng.org/gen-ttr/TTf1l3s/ALPHA_01178_200220115421.pdf

So a new Inverter is just as likely to come with the earthing issue as not if G98/G99 approved.

Wonder if MCS consider the earthing, as long as they get their fees I doubt it.

 

[Joseph_Martin]

UK approval ie G98/G99 is only for the DNO, ie that it shuts off in a controlled manner and turns back on in a controlled manner to protect the Grid. What it does as long as its not grid connected does not enter the test. If you look at the tests for this approval the earth is not part of the test even when grid connected, the DNO does not care about you being electrocuted only the linesmen and the Grid function.

https://www.ena-eng.org/gen-ttr/TTf1l3s/ALPHA_01178_200220115421.pdf

So a new Inverter is just as likely to come with the earthing issue as not if G98/G99 approved.

Wonder if MCS consider the earthing, as long as they get their fees I doubt it.

Thanks for that, I wasn't aware that not all the functionality of the inverter was subjected to approval. To be frank, safety approval seems to be a pretty sketchy process if it does not cover all safety-related issues with a bit of kit. As a consumer, who spent a not inconsiderable amount of money for something that was sold as being able to make better use of our solar power, to allow us to cut our bills by using less peak rate electricity, and, most importantly, have a system that provided safe back up power when the grid fails, I'm more than a bit astonished that not every safety-related aspect of the unit is considered when it comes to safety approval.

Assuming that the fix of adding the neutral to earth contact works OK, then the whole thing seems even more astonishing. Our electrician has indicated that the cost of the part needed is going to be around £20, which seems an extraordinarily low price for something that has the potential to change a system that has been condemned and isolated as being a serious hazard into a system that is considered safe and compliant with the safety regulations. It begs the question as to why the manufacturer, Sofar, didn't include this key safety requirement in their manual, as well as why the installer went ahead and installed a bit of kit that was demonstrably unsafe and potentially dangerous.

Perhaps I have a naive view of safety, but I had thought that all electrical appliances had to pass some sort of government mandated safety testing process (I'm of an age where the "kite mark" was the indicator of this). Even now, a couple of weeks after our electrician dropped this bombshell I'm still taken aback by the absence of solid safety-related information, or even concern, by the manufacturer. They seem far more interested in getting me to spend a lot more money with them to buy a replacement inverter, that as far as I can determine may well have the exact same failing. That there seems to be other manufacturers that are also selling potentially unsafe bits of kit is simply astonishing.

I have spent tens of hours looking into this, and to be fair, our electrician has been doing much the same, as he also wants to try and get our system back up and running again. Neither of us should have to go to such lengths to find an answer to such a serious safety issue, the manufacturer should have sorted this out before offering the product for sale in the first place. I still do not understand why they are silent on this, it seems to beggar belief given the hazard their product presents.

 

[kommando]

All electronic devices are covered by CE regs, but as with G98/G99 they are not tested by the regulators. The manufacture's are allowed to get tested by 3rd party 'Independent' testing companies. Guess how independent they are when the manufacture is paying the bill. Where the manufacture is not based in the country where the item is being sold then the testing data is supposed to be held by the importer/distributor within the country and to be produced on demand. Every time I have asked where the maker is Chinese the data is missing.

So best just assume that that CE label means absolutely nothing.

The manufacturing company I used to work for bought some machinery from Italy, it was stipulated the guarding was to be CE std and certified. When it arrived the guarding was none existent. So don't just assume China is the only source of fake CE labels.

 

[SeaGal]

So best just assume that that CE label means absolutely nothing.

I thought it meant Chinese Export

Seriously though...

Perhaps I have a naive view of safety, but I had thought that all electrical appliances had to pass some sort of government mandated safety testing process (I'm of an age where the "kite mark" was the indicator of this)

I suspect this issue here is that an inverter is not considered an 'electrical appliance'. It is a component of a complex system that needs to be installed by trained and knowledgeable people, rather than being plug-and-play.

Anyway, good you have a way forward