Why does my main house consumer unit trip when the inverter switched to AC backup?

Just to be sure - nothing you have done wrong - but would you measure the resistance between the two blue N connections at the bottom of the inverter box - see attached image and area circled in blue. If there are ac isolator switches on the the inverter box then please turn these on. As before all other power disconnected and isolated.

I am trying to establish whether the incoming N is permanently connected to the output N. (It may actually be a switched connection but at the moment I don't want to work on the cabinet when powered up.)

This link has a picture shwoing the internally linking of in N and out N:

Connection of Inverter Energy Systems to the Grid: New requirements surround residual current devices - GSES - https://www.gses.com.au/battery-storage-systems-what-are-their-chemical-hazards/

The tack I am following is that you have been sold a cabinet designed safely to take mains power from a generator which has an isolated neutral ie: not connected to earth E. When this generator is replaced by the UK mains supply the incoming mains N is connected to earth as the norm. Alas, your cabinet has an output N to E link as well which is troublesome when the inverter is in bypass/line mode ie mains supplying the output not the inverter. The effect of presenting your home's main RCD with an NE link before it and also after it is that not all the neutral current passes through it - some takes a different route via the two NE links. The net result is that the home RCD detects rightly a difference between the L and N and trips.

What some systems do is switch the output NE link in and out of circuit depending (respectively) on whether it is the inverter or mains supplying the output. At the same time the output has both L and N double pole switching between inverter LN and mains LN - at no time is the output connected to both Ns - that from the mains and that from the inverter. (Of course the switching also prevents both Ls from the mains and the inverter being connected to the output at the same time).

eg: Automatic Neutral-to-Ground Connection - https://www.sigineer.com/news/automatic-neutral-ground-connection/

Note that this is a US reference but it gives you the idea of what I describe.

What's important for safety is that for loads connected to the inverter cabinet output the N is always referred to E irrespective of whether the source of electrical power is the mains, a gennie or the inverter in order that fuses, mcbs, rcds, rcbos will operate in the event of an earth fault or earth leakage whether that be L to E or N to E.

AS this is a bought product, can you send me details of what you bought and from where and I while seek some technical clarification from the supplier/maker on what was intended in way of mains input.

Please do not change anything yet.

marconi said:

Just to be sure - nothing you have done wrong - but would you measure the resistance between the two blue N connections at the bottom of the inverter box - see attached image and area circled in blue. If there are ac isolator switches on the the inverter box then please turn these on. As before all other power disconnected and isolated.

I am trying to establish whether the incoming N is permanently connected to the output N. (It may actually be a switched connection but at the moment I don't want to work on the cabinet when powered up.)

This link has a picture shwoing the internally linking of in N and out N:

Connection of Inverter Energy Systems to the Grid: New requirements surround residual current devices - GSES - https://www.gses.com.au/battery-storage-systems-what-are-their-chemical-hazards/

The tack I am following is that you have been sold a cabinet designed safely to take mains power from a generator which has an isolated neutral. When this generator is replaced by the UK mains supply the incoming mains N is connected to earth as the norm. Alas, your cabinet has an output N to E link as well which is troublesome when the inverter is in bypass/line mode ie mains supplying the output not the inverter. The effect of presenting your home's main RCD with an NE link before it and also after it is that not all the neutral current passes through it - some takes a different route via the two NE links. The net result is that the home RCD detects rightly a difference between the L and N and trips.

What some systems do is switch the output NE link in and out of circuit depending (respectively) on whether it is the inverter or mains supplying the output. At the same time the output has both L and N double pole switching between inverter LN and mains LN - at no time is the output connected to both Ns - that from the mains and that from the inverter. (Of course the switching also prevents both Ls from the mains and the inverter being connected to the output at the same time).

eg: Automatic Neutral-to-Ground Connection - https://www.sigineer.com/news/automatic-neutral-ground-connection/

Note that this is a US reference but it gives you the idea of what I describe.

What's important for safety is that for loads connected to the inverter cabinet output the N is always referred to E irrespective of whether the source of electrical power is the mains, a gennie or the inverter in order that fuses, mcbs, rcds, rcbos will operate in the event of an earth fault or earth leakage whether that be L to E or N to E.

AS this is a bought product, can you send me details of what you bought and from where and I while seek some technical details from the supplier/maker and what was intended in way of mains input.

Please do not change anything yet.

Click to expand...

Hello Marconi

I measured between the two Neutrals at the input and output on the inverter and got no result at all.

The cabinet we bought is an SP5048 silent power plug and play 5kw that has an axpert MKS 4 inverter (5.6 kw) and not the voltacon V7 (yellow 5 kw inverter) that is in the product description. I am assuming that the actual cabinet layout and controls are the same for both model of inverter but I am by no means sure.
The company are Voltacon UK Ltd in Coventry
I believe I mentioned previously that the inverter has a fault F12 which is a dc/dc overcurrent issue that I have still to rectify possible by returning it to the supplier. Someone on another forum seemed to think that this is an MPPT issue.
I am hoping that this fault albeit on the P.V. side of things is not having any effect on the AC side of things.

I would be interested to see how forthcoming they are to you and that they can provide some sort of specific answer.

I will not be able to get back to you now until the weekend as my work commitments mean I am out of the house.

Many thanks for the help

Regards

Tonyboy

By way of clarification, that box marked Cronos Voltage is measuring the input voltage between L and N and checking it is within range ie say 230V +/- 10V, and if it is it then closes a contact which then applies power to the contactor next to it to supply power to the input of the inverter. If the voltage goes out of range then the relay contacts open, the contactor opens and thereby removes power from the inverter. There is a delay of 4s to close the contacts when the voltage is 'good' but they are opened instantaneously if not.

https://www.cronos-electronics.gr/faseon_en.htm

@Tonyboy
Has your electrical installation ever been inspected and tested and if it has was anything mentioned about low or unusual insulation resistance?

Have you had an electrician look at this problem?

It would be sensible to ensure that the RCD in the consumer unit is working correctly and that there is not a fault elsewhere in the installation that may be the underlying problem behind this issue.

I would also advise having an electrician look at the earthing arrangements for this system as you seem to be unsure about this. Poor or incorrect connection of the earthing, particularly as it sounds like there is a N-E link in this cabinet, may be causing your issues and may have resulted in there being unexpected dangers present.

Tonyboy: I have sent this to Voltacon:




To: [email protected];
17/02/2023 06:43
1

Silent Power SP5048-C-P, PLUG 'N' PLAY PHOTOVOLTAIC CONTROL CABINET Off Grid Inverter Charger Kit 5000Watt -

https://voltaconsolar.com/silent-power-sp5048-c-p.html

Dear Sir or Madam,

May I clarify something about the ac input to the Silent Power SP5048?

I have a client with this product which works fine until the ac input from the home mains is connected. When the domestic 230V ac 50Hz single phase supply is connected to the inverter the home consumer unit residual current detector trips cutting off this supply. I am helping him find out why. He tells me he bought the product from you with the expectation it could be connected to his home's mains supply, albeit he is not completely au fait with electrical jargon since he is not an electrician or electrical engineer so he may have misunderstood.

I note that the literature at reference describes the SP5048 as an 'off-grid' system and that pictorial schematic shows a generator providing the external 230V ac supply and not the mains. Indeed it also describes contacts and soft start for a generator supply.

I note too that the output ac is via an RCD and the supply is described as TN-S. This indicates to me that there is a Neutral to Earth link before the ac output RCD. I have measured with an Ohmmeter the low continuity resistance and thus presence of this link. The presence of this link would cause the domestic consumer unit RCD to trip because the mains supply already has its neutral connected to earth; the situation thus arises where there is a N-E link both before and after the home CU RCD with the inevitable result that it will detect an unbalanced current because not all the N current passes through the home RCD - some flows through the path created by the two N-E links.

So this seems to confirm to me - but I would appreciate your clarification please - that the SP5048 is not intended to be connected to the UK mains supply. It is as described in the literature, an off-grid system only meant to be connected to a back-up generator. Am I correct?

Yours sincerely


BSc(Hons) CEng MIET
Chartered Electrical Engineer

davesparks said:

@Tonyboy
Has your electrical installation ever been inspected and tested and if it has was anything mentioned about low or unusual insulation resistance?

Have you had an electrician look at this problem?

It would be sensible to ensure that the RCD in the consumer unit is working correctly and that there is not a fault elsewhere in the installation that may be the underlying problem behind this issue.

I would also advise having an electrician look at the earthing arrangements for this system as you seem to be unsure about this. Poor or incorrect connection of the earthing, particularly as it sounds like there is a N-E link in this cabinet, may be causing your issues and may have resulted in there being unexpected dangers present.

Click to expand...

Hi Davesparks
I have contacted a chap who is a solar installer electrician to see if he can have a look at things for me, he is away at present so in the interim I am trying to work through a number of tests with another member of the forum. I am grateful for your reply and hope in the next week to have had some response from the electrician. Regards and thanks Tonyboy

marconi said:

Tonyboy: I have sent this to Voltacon:

To: [email protected];
17/02/2023 06:43
1

Silent Power SP5048-C-P, PLUG 'N' PLAY PHOTOVOLTAIC CONTROL CABINET Off Grid Inverter Charger Kit 5000Watt -

Silent Power SP5048-C-P, PLUG 'N' PLAY PHOTOVOLTAIC CONTROL CABINET Off Grid Inverter Charger Kit 5000Watt - https://voltaconsolar.com/silent-power-sp5048-c-p.html

Dear Sir or Madam,

May I clarify something about the ac input to the Silent Power SP5048?

I have a client with this product which works fine until the ac input from the home mains is connected. When the domestic 230V ac 50Hz single phase supply is connected to the inverter the home consumer unit residual current detector trips cutting off this supply. I am helping him find out why. He tells me he bought the product from you with the expectation it could be connected to his home's mains supply, albeit he is not completely au fait with electrical jargon since he is not an electrician or electrical engineer so he may have misunderstood.

I note that the literature at reference describes the SP5048 as an 'off-grid' system and that pictorial schematic shows a generator providing the external 230V ac supply and not the mains. Indeed it also describes contacts and soft start for a generator supply.

I note too that the output ac is via an RCD and the supply is described as TN-S. This indicates to me that there is a Neutral to Earth link before the ac output RCD. I have measured with an Ohmmeter the low continuity resistance and thus presence of this link. The presence of this link would cause the domestic consumer unit RCD to trip because the mains supply already has its neutral connected to earth; the situation thus arises where there is a N-E link both before and after the home CU RCD with the inevitable result that it will detect an unbalanced current because not all the N current passes through the home RCD - some flows through the path created by the two N-E links.

So this seems to confirm to me - but I would appreciate your clarification please - that the SP5048 is not intended to be connected to the UK mains supply. It is as described in the literature, an off-grid system only meant to be connected to a back-up generator. Am I correct?

Yours sincerely


BSc(Hons) CEng MIET
Chartered Electrical Engineer

Click to expand...

Hi Marconi
Many thanks for the help in this, I will wait with interest to see what the reply contains.

I know this is a bit off topic from the one you are helping me with but I was wondering if you had any thought about this;
I am currently also faced with the prospect of taking the inverter back to the supplier myself, as it is not working correctly. On re testing the pv Voltage at the input to the cabinet I have now seen it peak from what was 258v DC which is what I get from the 7x 420 w panels as their VOC.

I checked this at the point before I connected the cabinet as it has an input limit of 500vdc and it was fine, then after the F12 fault occurred I checked it again and found it went from 350 to 450 or more at the connection to the cabinet. I have since disconnected the PV from the cabinet as someone else told me that this could be damaging my solar panels.
The response from the supplier regarding the F12 fault was it was an mppt issue and the inference was that I had somehow caused it. Since I have only connected the PV, the batteries and the two plugs I can't see how but I will have to wait until they test it to see what they determine the fault is.

I subsequently started the inverted connected to the batteries but with the external PV isolator off and measured the input voltage on the pv inside the cabinet. With the internal isolator off the was 0vdc but as soon as the internal switch was on the reading was 150-180vdc at the input which can't be right. I know mppt is designed to get the best out of panels and in particular to assist if a panel is part shaded but I can't really say with any certainty that this may be the cause of the increased voltage at the pv input.
Do you have any experience of inverter mppt issues and if so are you able to shed any light on what may be causing this problem too. If you would prefer me to start a new topic for this then of course I will as I don't wish to cause any issues on the forum particularly as you have been so helpful.

Frankly at the moment I am beginning to wonder what I have bough and if I would not have been better buying all of the parts separately and installing them on a board in the cupboard to my own design. I wanted a self contained unit as it negated the need to size and design the contents myself but as it stands it has not fulfilled the requirement of a "plug and play unit". Don't get me wrong I realise there may have been issues if I had done this the other way too and that the problem may be resolved some how with a relatively easy solution. I am waiting for a solar installer electrician to contact me next week as he is away at present. Hopefully he can have a look at my system and test the earth and the protection device in the house, who knows it may be my house that is the issue!
As ever I am really grateful for your time and assistance in this and look forward to hearing from you again and moreover what response you receive to your request.

Regards

Tonyboy

Tonyboy: I had a reply from Voltacon Conventry but it did not address my clarification with rigour so I have sent a further missive to them. Helpfully, they said they would study the wiring in of the cabinet so I have sent them your sketch with some additional bits by me and a drawing of how you have connected the cabinet into your home's consumer unit.

The detail of terminology matters. An off-grid system means exactly that; not at all connected to the nations electricity grid network. It may though be connected to a generator or other form of generation but not the mains electricity grid.

An on-grid system is connectable to the mains electricity grid, to provide back up, exploitation of off peak electricity and if arranged the export of surplus solar generation to the grid to earn payments from your mains electricity supplier.

Expanding on 'on-grid' a little, in order to export electrical energy to the grid, the inverter ac output technology has to be suited to connect in parallel with the incoming mains grid ac supply. The phrase 'grid-tie' is used for an ac connection between the mains and solar charger/inverter which facilitates a two-way flow of ac electrical power - from mains the mains to consume and to the mains to export. For safety reasons, a solar/charger inverter which is grid-tied has functionality to detect at all times the existence of the mains supply and in the event of a power cut it severs the grid-tie so that 240Vac 50Hz power produced by the inverter does keep (attempt to keep) the wiring in the installation and the mains distribution network your homes is connected to alive which would be hazard.

It is clear to me (at least for now unless Voltacon convince me otherwise) that your cabinet is an off-grid system. It is not intended to be connected to the mains. Indeed, as I have already pointed out, the cabinet and Voltacon too in their blurb describe it as an off-grid system. To do what you want to achieve - mains back up of the ac output and exploitation of mains off-peak electricity to charge the battery you should have bought an on-grid system. You did not require an on-grid grid tied system unless you wanted to export to the grid. On this point was it your wish to export to the grid to earn a feed-in payments? Feed in payment rates per kWh are quite low compared (pennies) with bought kWh (tens of pennies) so the best economic return is so-called self-consumption as solar power is produced or from stored power in batteries charged by solar (and wind) power.

Your current system is ill-suited to on-grid operation because in order to provide earth fault protection on the ac output side the neutral of the output must be connected to an earth reference. I will expand on this point about earthing in another post with some drawings to illustrate some current flows in neutrals and earth conductors and why the output rcd and mcb requires an earth connected neutral and why doing this on the output can causes the trip of an rcd present in the ac input feed.

I will ponder a work around for your current cabinet but just wanted to say early on you have mistakenly bought (in my opinion) an off grid system when you should have bought an on-grid one. You may have though a case for the mistake being with the supplier if you either asked for an on-grid system and they sent you instead an off-grid, or you described to the supplier what you wanted to achieve and they recommended sold you an off-grid system.

I will work up the diagrams over the next couple of days. Meanwhile have a look and read through this again and nota bene the absence of anything to do with connection to the mains and the schematic - concept of operation.

Silent Power SP5048-C-P, PLUG 'N' PLAY PHOTOVOLTAIC CONTROL CABINET Off Grid Inverter Charger Kit 5000Watt - https://voltaconsolar.com/silent-power-sp5048-c-p.html

A dead give-away that it is not meant to be on-grid is that the input ac power is via a c form plug. An on-grid system (which can operate in line/bypass mode ie output supplied by input grid mains) relies on an output earth referenced neutral derived from the input earth referenced neutral (and thus no need for an N-E link on the ac output side) the ac input must hard-wired in.

One can have systems which provide a switchable N-E link on the output depending on whether the system is in line/bypass mode - I introduced you to this idea earlier and this could - not saying it is right now - a potential solution but I need to check the UK regulations and of course locate where the link is made in the cabinet you bought.

My second email:

Thank you for your prompt response. I have attached two images. The DSC was produced by the client and shows in black how he has connected the SP cabinet. I have added to it in outline the connections to his home's consumer unit which is identified in this image as the two blue boxes. (A bit rough but I am sat waiting for my wife to have an XRAY so please excuse the standard of drawing).
In the second image - HOME CU - I have sketched how the ac supply is derived to feed to the SP cabinet. His home has the usual cutout, feeding a meter and main earth terminal. L and N from the meter and an E from the main earth terminal connect to the consumer unit. The consumer unit has a combined mainswitch and residual current circuit breaker which covers all the outgoing circuit breakers. One of these circuit breakers is a 32A one for the SP cabinet. Between the consumer unit and the SP cabinet is a 3 core cable with L, N and E which connects into a c form socket. This cform socket connects to the SP cabinet's ac input c form plug. There is an ac input isolator in this cable just before the c form socket - ie external to the SP cabinet.
Happy to amplify further when I am home but I hope these drawings give you the gist.

marconi said:

Tonyboy: I had a reply from Voltacon Conventry but it did not address my clarification with rigour so I have sent a further missive to them. Helpfully, they said they would study the wiring in of the cabinet so I have sent them your sketch with some additional bits by me and a drawing of how you have connected the cabinet into your home's consumer unit.

The detail of terminology matters. An off-grid system means exactly that; not at all connected to the nations electricity grid network. It may though be connected to a generator or other form of generation but not the mains electricity grid.

An on-grid system is connectable to the mains electricity grid, to provide back up, exploitation of off peak electricity and if arranged the export of surplus solar generation to the grid to earn payments from your mains electricity supplier.

Expanding on 'on-grid' a little, in order to export electrical energy to the grid, the inverter ac output technology has to be suited to connect in parallel with the incoming mains grid ac supply. The phrase 'grid-tie' is used for an ac connection between the mains and solar charger/inverter which facilitates a two-way flow of ac electrical power - from mains the mains to consume and to the mains to export. For safety reasons, a solar/charger inverter which is grid-tied has functionality to detect at all times the existence of the mains supply and in the event of a power cut it severs the grid-tie so that 240Vac 50Hz power produced by the inverter does keep (attempt to keep) the wiring in the installation and the mains distribution network your homes is connected to alive which would be hazard.

It is clear to me (at least for now unless Voltacon convince me otherwise) that your cabinet is an off-grid system. It is not intended to be connected to the mains. Indeed, as I have already pointed out, the cabinet and Voltacon too in their blurb describe it as an off-grid system. To do what you want to achieve - mains back up of the ac output and exploitation of mains off-peak electricity to charge the battery you should have bought an on-grid system. You did not require an on-grid grid tied system unless you wanted to export to the grid. On this point was it your wish to export to the grid to earn a feed-in payments? Feed in payment rates per kWh are quite low compared (pennies) with bought kWh (tens of pennies) so the best economic return is so-called self-consumption as solar power is produced or from stored power in batteries charged by solar (and wind) power.

Your current system is ill-suited to on-grid operation because in order to provide earth fault protection on the ac output side the neutral of the output must be connected to an earth reference. I will expand on this point about earthing in another post with some drawings to illustrate some current flows in neutrals and earth conductors and why the output rcd and mcb requires an earth connected neutral and why doing this on the output can causes the trip of an rcd present in the ac input feed.

I will ponder a work around for your current cabinet but just wanted to say early on you have mistakenly bought (in my opinion) an off grid system when you should have bought an on-grid one. You may have though a case for the mistake being with the supplier if you either asked for an on-grid system and they sent you instead an off-grid, or you described to the supplier what you wanted to achieve and they recommended sold you an off-grid system.

I will work up the diagrams over the next couple of days. Meanwhile have a look and read through this again and nota bene the absence of anything to do with connection to the mains and the schematic - concept of operation.

Silent Power SP5048-C-P, PLUG 'N' PLAY PHOTOVOLTAIC CONTROL CABINET Off Grid Inverter Charger Kit 5000Watt - https://voltaconsolar.com/silent-power-sp5048-c-p.html

A dead give-away that it is not meant to be on-grid is that the input ac power is via a c form plug. An on-grid system (which can operate in line/bypass mode ie output supplied by input grid mains) relies on an output earth referenced neutral derived from the input earth referenced neutral (and thus no need for an N-E link on the ac output side) the ac input must hard-wired in.

One can have systems which provide a switchable N-E link on the output depending on whether the system is in line/bypass mode - I introduced you to this idea earlier and this could - not saying it is right now - a potential solution but I need to check the UK regulations and of course locate where the link is made in the cabinet you bought.

My second email:

Thank you for your prompt response. I have attached two images. The DSC was produced by the client and shows in black how he has connected the SP cabinet. I have added to it in outline the connections to his home's consumer unit which is identified in this image as the two blue boxes. (A bit rough but I am sat waiting for my wife to have an XRAY so please excuse the standard of drawing).
In the second image - HOME CU - I have sketched how the ac supply is derived to feed to the SP cabinet. His home has the usual cutout, feeding a meter and main earth terminal. L and N from the meter and an E from the main earth terminal connect to the consumer unit. The consumer unit has a combined mainswitch and residual current circuit breaker which covers all the outgoing circuit breakers. One of these circuit breakers is a 32A one for the SP cabinet. Between the consumer unit and the SP cabinet is a 3 core cable with L, N and E which connects into a c form socket. This cform socket connects to the SP cabinet's ac input c form plug. There is an ac input isolator in this cable just before the c form socket - ie external to the SP cabinet.
Happy to amplify further when I am home but I hope these drawings give you the gist.

Click to expand...

Hi Marconi
As ever many thanks for the in depth reply. I do though need to tell you that the kit in the link you have above is not the one I purchased, (though I note it has the same reference and incidentally that there is also a third cabinet listed as an SP5048 too). As well as this the cabinet I received did not contain the inverter shown, but all the wiring and layout is the same. Also I need to clarify something regarding the drawings you have sent to Voltacon and the expectations of the system I purchased.

Firstly here is the link to the cabinet I purchased (stating that it can be charged from the grid) - Silent Power 5Kw Off Grid Inverter Cabinet 6kW Solar PV 48V/230VAC (voltaconsolar.com)
and here is a link to the (off grid) inverter that the cabinet actually contained when it arrived (though I have not raised this issue with them, as I believe the inverter supplied is a better model than that shown in the listed cabinet - Conversol VM 4. Solar Off Grid Inverter 5.6kW. PV Input 6kW. Wi-Fi, BMS & Wi-Fi (voltaconsolar.com)

In the many conversations I have had with the supplier for 4 months prior to purchasing the kit, I made them aware that I was intending to provide power to my home from a separate consumer unit unconnected with the grid and that I was going to store power in batteries when the solar was not producing power. I also wanted a means to charge the batteries in the event we had a long period with no solar, to this ends I was advised that the off grid cabinet was suitable and it could be supplied with supplementary power from either a generator or the grid. I told them I was not going to have a generator and was accordingly advised the system was fine to be connected to the grid via plugs as it has no means of returning power to the grid in the event of a power failure in the grid supply. I did challenge them a couple of times over this issue as I did not want something that would be a danger to anyone working on the incoming main supply in the event of a power failure. I am aware grid tied inverters have an islanding requirement and I think at the time I quoted this to Voltacon and the response was the system physically had no way to return power to the grid.

My system is this; I have the cabinet, batteries and solar panels connected to the SP cabinet in a purpose built fire proof cupboard outside of the house and I have a completely separate consumer unit in the cupboard that supplies solar only supplied power into the property via separate supply and power points in each room. The input to the cabinet is from a single 32 amp supply from the mains consumer unit in the house via an isolator in the solar cupboard then into the cabinet via the c plug.

In the picture of the cabinet and panels that you have sent I do not have the earth from the panels connected back to the incoming mains at the point it goes into the cabinet via the c plug. Currently I have the panel & frames earthed to the bus bar and am waiting to find out if it is better to run this to a separate ground rod in the garden for the purposes of the panels protection. I was under the impression that connecting the panels to the cabinet and equipment was not a good idea in the event of a lightning strike/induced current etc. I am not using the solar system at present so I have no issues with the earthing arrangement not being complete and will on advice do the best thing required. I have the batteries on a ground rod but am happy to put a rod outside in a separate location nearer the panels and frames.

The 32 amp supply from the incoming consumer unit has a line neutral and earth to the isolator in the solar cupboard outside and then into the cabinet via the plug with L,N and E.
I can see that given the issues at present, the earth is what I assume is causing the problems, as in the event of power failure from the grid there is still a connection via the earth through the neutral from the cabinet back to the incoming neutral at my incoming mains consumer unit.

In respect of the earth reference for the separate solar AC output to my home from the sp cabinet, I was also thinking that if I provided a ground rod connection to this, then the appliances in the home would not be connected to the grid other than through the c plug arrangement and would have a path to earth of their own.
I had initially considered if it was possible to remove the earth from the c plug out of the sp cabinet or somewhere else perhaps inside the cabinet and connect the solar consumer unit earth with a ground rod. This would then remove the connection between my solar consumer unit and the incoming consumer unit. I am not at all familiar with the requirements of this so it is only something I had thought about as a solution.

I am extremely grateful for the detailed help you are giving me, so want to ensure that the details Voltacon get are absolutely correct as any solution they may provide will be determined by the details they have to work with and given their quite unhelpful approach to me I do not want them thinking I have something that I don't. Moreover I don't want to waste your time working on inaccurate information. To summarize, all I am looking to achieve is an off-grid power supply to my separate off-grid sockets in the house, that can only when needed, have it's batteries re-charged from the low tariff night time mains supply.

Many thanks and regards

Tonyboy

I will mull over what have sent me which will make my rail journey North next week pass quickly. I was cooking a three course meal for 50 last night in our church social club so am a bit weary today for any serious thinking. But a quick question now - is the dedicated consumer unit for off grid sockets in the same building as all the other final circuits (ie sockets, lights, cooker etc) fed by your MEM Consumer Unit shown in #1? Do you have two types of sockets - 'grid' and 'off grid' and marked as such? And please post a picture of your cut out and the earth terminal so I can work out the earthing system. Is your supply overhead or underground? A few pictures saves me asking further questions.

Oh one more question- what ‘output source priority‘ option have you selected for the ac output‘s source of power Eg usb, sbu, sub? Is line/bypass mode enabled or disabled? Similarly what is the selected battery charging priority option?

ps: I have not yet read your axpert box‘s manual but would not be surprised if it is a standard white box akin to iconica and voltacon with an axpert badge stuck on. I have designed off grid solar systems with genie input and battery storage using the voltacon 5kW hybrid box.

marconi said:

I will mull over what have sent me which will make my rail journey North next week pass quickly. I was cooking a three course meal for 50 last night in our church social club so am a bit weary today for any serious thinking. But a quick question now - is the dedicated consumer unit for off grid sockets in the same building as all the other final circuits (ie sockets, lights, cooker etc) fed by your MEM Consumer Unit shown in #1? Do you have two types of sockets - 'grid' and 'off grid' and marked as such? And please post a picture of your cut out and the earth terminal so I can work out the earthing system. Is your supply overhead or underground? A few pictures saves me asking further questions.

Oh one more question- what ‘output source priority‘ option have you selected for the ac output‘s source of power Eg usb, sbu, sub? Is line/bypass mode enabled or disabled? Similarly what is the selected battery charging priority option?

ps: I have not yet read your axpert box‘s manual but would not be surprised if it is a standard white box akin to iconica and voltacon with an axpert badge stuck on. I have designed off grid solar systems with genie input and battery storage using the voltacon 5kW hybrid box.

Click to expand...

Hello Marconi
You certainly sound like a busy chap, I do hope that you get some rest before the trip tomorrow.

The consumer unit for the solar is in the external cupboard to be labelled as solar and not in the house. I have two types of sockets one for solar and one for the providers power, solar to be labelled as such when finished. I have attached a pic of the kitchen sockets) black is solar.
The incoming main supply is overhead and then in through the wall of the house to the meter and consumer unit. (also attached is earth arrangement in consumer unit).

I have output source set to SBU and I believe bypass mode must be enabled as when the timer is set to use the utility at night for charging it then makes power available to the loads as well as charging the batteries (albeit we would not be using any loads).
I have also attached a copy of the setup doc sent by the supplier with their recommended settings.

Battery charging priority is Solar only currently, recommended by supplier but I can set it to solar and then utility as I believe this is necessary to enable overnight charge from utility. This was set previously to solar then utility when we tested the utility charging timer on the inverter and it tripped the main switch in the house.

I am aware that you are busy so please reply when you have the time. I have to send the inverter back after it is removed next weekend so I am not in a rush as I doubt I will have the inverter back for a while yet.

As ever many thanks for the help and advice and have a safe trip.

Regards

Tonyboy

Very helpful information which casts much light on the problem. It says an up-front rcd is 'not recommended' - rather weak language methinks. It either is or is not required. Anyway, with more mental energy than last time I have the outline of a solution. But before I desrcibe it and also before you disconnect and return the axpert box, would you have time to do a simple test?

With solar, battery and mains all isolated first could you work through the next few steps?

What I want to establish is that it is the presence of an N-E link on the output which is causing your MEM CU RCD to trip when the box enters bypass and utility battery charging modes. To do this would you simply disconnect the line and neutral (coloured black and blue) from the output terminals on the Axpert box. Put each cable into its own connector to keep the bare ends covered.

With a multimeter on low Ohms range measure the resistance between the N and E ac output terminals on the Axpert box - I expert it to be very high resistance/off the scale. (#)

Now measure between the black and blue cables which are in the two connectors - with the output mcb on and the output rcd off. I expect the reading to be very low.

Now, set up the Axpert box so that you can charge the battery from the utility. You do not have to wait until the off peak tariff period - select a time during the day suited to the time you are going to do the test. The battery charging priority must be selected to put utility first.

Now, before the charging time slot period starts, power up the solar and battery and ac mains input. Keep the ac output disconnected. Wait till the charging time slot starts and see if the MEM rcd trips when the utility starts to charge the battery and bypass connected the ac input to the ac output(which of course is disconnected from any loads).

With this test there is no N-E link on the output, unless it is done inside the box but those two Ohmmeter checks will discover if this is the case if you find a low resistance reading between N and E at the box terminals - see # above.

I 'hope' we find the MEM rcd does not trip. If it does then it indicates another type of problem.

If this is not clear then I will amplify for you.

marconi said:

Very helpful information which casts much light on the problem. It says an up-front rcd is 'not recommended' - rather weak language methinks. It either is or is not required. Anyway, with more mental energy than last time I have the outline of a solution. But before I desrcibe it and also before you disconnect and return the axpert box, would you have time to do a simple test?

With solar, battery and mains all isolated first could you work through the next few steps?

What I want to establish is that it is the presence of an N-E link on the output which is causing your MEM CU RCD to trip when the box enters bypass and utility battery charging modes. To do this would you simply disconnect the line and neutral (coloured black and blue) from the output terminals on the Axpert box. Put each cable into its own connector to keep the bare ends covered.

With a multimeter on low Ohms range measure the resistance between the N and E ac output terminals on the Axpert box - I expert it to be very high resistance/off the scale. (#)

Now measure between the black and blue cables which are in the two connectors - with the output mcb on and the output rcd off. I expect the reading to be very low.

Now, set up the Axpert box so that you can charge the battery from the utility. You do not have to wait until the off peak tariff period - select a time during the day suited to the time you are going to do the test. The battery charging priority must be selected to put utility first.

Now, before the charging time slot period starts, power up the solar and battery and ac mains input. Keep the ac output disconnected. Wait till the charging time slot starts and see if the MEM rcd trips when the utility starts to charge the battery and bypass connected the ac input to the ac output(which of course is disconnected from any loads).

With this test there is no N-E link on the output, unless it is done inside the box but those two Ohmmeter checks will discover if this is the case if you find a low resistance reading between N and E at the box terminals - see # above.

I 'hope' we find the MEM rcd does not trip. If it does then it indicates another type of problem.

If this is not clear then I will amplify for you.

Click to expand...

Good morning Marconi
glad to hear you are refreshed.

I am just off to the hospital with my wife so I will not be able to do the tests until probably Wednesday am.
I am happy to do as requested and will work through the print out of these instructions as I go.

My only issue at present is that with the solar connected to the pv input on the cabinet I am getting 120 -200 v dc back out of the input terminals with the panels isolated from the cabinet and the pv isolator on in the cabinet. This has led me to some concerns over connecting the pv back to the input of the cabinet in fear of the increased voltage up around 450+ when last measured and the possibility of the added voltage causing damage to my panels.

If I can do the test with the pv isolated (running the inverter on the batteries) and it will yield the same results then I would prefer that rather than risk and damage to my panels.

Let me know if this will cause any issue and I hope to get back to you as soon as I return.

As ever I am grateful for your help

Regards

Tonyboy

Tonyboy said:

Good morning Marconi
glad to hear you are refreshed.

I am just off to the hospital with my wife so I will not be able to do the tests until probably Wednesday am.
I am happy to do as requested and will work through the print out of these instructions as I go.

My only issue at present is that with the solar connected to the pv input on the cabinet I am getting 120 -200 v dc back out of the input terminals with the panels isolated from the cabinet and the pv isolator on in the cabinet. This has led me to some concerns over connecting the pv back to the input of the cabinet in fear of the increased voltage up around 450+ when last measured and the possibility of the added voltage causing damage to my panels.

If I can do the test with the pv isolated (running the inverter on the batteries) and it will yield the same results then I would prefer that rather than risk and damage to my panels.

Let me know if this will cause any issue and I hope to get back to you as soon as I return.

As ever I am grateful for your help

Regards

Tonyboy

Click to expand...

Could you revise what you wrote in bold above please so it says what you meant a little clearer for me?

marconi said:

Could you revise what you wrote in bold above please so it says what you meant a little clearer for me?

Click to expand...

Hello Marconi

The issue with the pv input is this.

When I measure the pv input from the roof at the point it connects into the cabinet input connections (lower left in picture) I get the expected 253 vdc.
When the inverter is switched on but the isolator in the cabinet is off (lower right in picture), the voltage from the pv remains constant, when I then turn on the isolator in the cabinet for the pv, the voltage goes up to between 350 and 450 vdc.

When this happened I then isolated the pv supply using the external isolator I have fitted before the cabinet. Which effectively removes any input to the inverter from the pv, I then measured the voltage at the input connection to the cabinet and found the 100 to 200 vdc appearing at the input of the pv in the cabinet. If I turn off the isolator in the cabinet the voltage drops to zero, this led me to conclude that the dc voltage was coming from the inverter out through the input terminals in the cabinet.
Now I have no idea of how this is possible as this would indicate that the inverter is working totally incorrectly or that the inverter is somehow sending power to the point it is supposed to be taking it in.

When the inverter is on and working it only shows 252 vdc input from the pv (see Right hand pic) on the front panel of the inverter and it was not until I re measured the voltages of all of the terminals in the cabinet whilst trying to find any indication of what may be causing the problems I am having I discovered this issue.

I am somewhat concerned that this may be down to a wiring issue in the cabinet or the inverter but it is difficult to determine which without removing more wiring. Perhaps when I come to remove the inverter this weekend I will measure the voltage at the input connection to the actual inverter with all wiring removed to see if it is as above, when there are no other routes for the voltage from the inverter itself.

Feel free to ask for more information if this is required

Many thanks as ever and Regards

Tonyboy

Tonyboy said:

Hello Marconi

The issue with the pv input is this.

When I measure the pv input from the roof at the point it connects into the cabinet input connections (lower left in picture) I get the expected 253 vdc.
When the inverter is switched on but the isolator in the cabinet is off (lower right in picture), the voltage from the pv remains constant, when I then turn on the isolator in the cabinet for the pv, the voltage goes up to between 350 and 450 vdc.

When this happened I then isolated the pv supply using the external isolator I have fitted before the cabinet. Which effectively removes any input to the inverter from the pv, I then measured the voltage at the input connection to the cabinet and found the 100 to 200 vdc appearing at the input of the pv in the cabinet. If I turn off the isolator in the cabinet the voltage drops to zero, this led me to conclude that the dc voltage was coming from the inverter out through the input terminals in the cabinet.
Now I have no idea of how this is possible as this would indicate that the inverter is working totally incorrectly or that the inverter is somehow sending power to the point it is supposed to be taking it in.

When the inverter is on and working it only shows 252 vdc input from the pv (see Right hand pic) on the front panel of the inverter and it was not until I re measured the voltages of all of the terminals in the cabinet whilst trying to find any indication of what may be causing the problems I am having I discovered this issue.

I am somewhat concerned that this may be down to a wiring issue in the cabinet or the inverter but it is difficult to determine which without removing more wiring. Perhaps when I come to remove the inverter this weekend I will measure the voltage at the input connection to the actual inverter with all wiring removed to see if it is as above, when there are no other routes for the voltage from the inverter itself.

Feel free to ask for more information if this is required

Many thanks as ever and Regards

Tonyboy

View attachment 106299 View attachment 106300

Click to expand...

I will do the same measurements on one of my brother in law’s solar leccy vans and see what I measure. Don’t think it is a problem but best to be sure.

Give us a clue, how old is the MEM distribution board and installation? 25 to 35 years old? And going off the PV system diagram in The Big Blue Book your array should be connected to the main earth bar, it`s not for lightning protection but electrical safety. Chances are you are getting a cumlative "overload " of the earth fault detection on the MEM rcd from all the circuits and devices connected. And if there`s a B type rcd in the inverter cab, the AC shouldn`t be upstream of it as indicated by the hieracy of rcds diagrams. You might even have to fit an isolating transformer. The suppliers instructions should have detailed all this.

marconi said:

I will do the same measurements on one of my brother in law’s solar leccy vans and see what I measure. Don’t think it is a problem but best to be sure.

Click to expand...

Hi Marconi
I am much obliged, I will do the tests tomorrow morning before I go out at lunchtime. Hopefully the results will elicit an answer.

Many thanks

Tonyboy

ukiri said:

Give us a clue, how old is the MEM distribution board and installation? 25 to 35 years old? And going off the PV system diagram in The Big Blue Book your array should be connected to the main earth bar, it`s not for lightning protection but electrical safety. Chances are you are getting a cumlative "overload " of the earth fault detection on the MEM rcd from all the circuits and devices connected. And if there`s a B type rcd in the inverter cab, the AC shouldn`t be upstream of it as indicated by the hieracy of rcds diagrams. You might even have to fit an isolating transformer. The suppliers instructions should have detailed all this.

Click to expand...

ukiri said:

Give us a clue, how old is the MEM distribution board and installation? 25 to 35 years old? And going off the PV system diagram in The Big Blue Book your array should be connected to the main earth bar, it`s not for lightning protection but electrical safety. Chances are you are getting a cumlative "overload " of the earth fault detection on the MEM rcd from all the circuits and devices connected. And if there`s a B type rcd in the inverter cab, the AC shouldn`t be upstream of it as indicated by the hieracy of rcds diagrams. You might even have to fit an isolating transformer. The suppliers instructions should have detailed all this.

Click to expand...

Hello ukiri
Many thanks for the reply
Yes the MEM is probably at least 25 year's old. I have a separate earth rod for the batteries adjacent to the kit in the external cupboard and as all of the supplies from the solar consumer unit are completely separate from the MEM I was going to connect the panels back to this and not to the incoming supply earth.
As for suppliers instructions well I got the inverter and Bluetooth battery monitor manuals and nothing else, hence the ongoing thread and the advice I have been getting.
Many thanks for the reply and if the tests I do today do not help I will look into an isolating transformer. I am assuming this is something you fit between the ac input to the cabinet and the ac input to the invetrer and the isolation part is isolation of the earth back to the grid supply?
Regards
Tonyboy

marconi said:

I will do the same measurements on one of my brother in law’s solar leccy vans and see what I measure. Don’t think it is a problem but best to be sure.

Click to expand...

Good Morning Marconi

I have carried out the requested tests. Multi- meter set on 200ohms lowest setting.

Measured between N and E on output terminals reading was 00.2 not very high.
The measurement between the two cables with output mcb on and output rcd off, no reading at all just the decimal point.

Set up the inverter to charge from the AC input but I have left the PV isolated as I am still not sure if the readings at the input terminals are an issue.

Timer came to start and ac started charging the batteries at 10 amps (I have set this limit), mains in house not tripped and still charging as I type.

Not sure why there is no reading on the two cables (black and Blue) as the meter is showing 00.1 when I touch the terminals together as a test.

I am going to let the inverter charge the batteries for the period I have set to see if it keeps going.

I hope the results are able to help and I look forward to hearing what you think is needed next.

As ever many thanks for the help.

Regards

Tonyboy

What I am working up as a solution is a very fast ac changeover switch to connect the ac output socket to either the inverter or the incoming grid mains but never both. Would you be happy with the changeover which happens within a few cycles of the ac mains so should not be noticeable?

Tonyboy said:

Good Morning Marconi

I have carried out the requested tests. Multi- meter set on 200ohms lowest setting.

Measured between N and E on output terminals reading was 00.2 not very high.
The measurement between the two cables with output mcb on and output rcd off, no reading at all just the decimal point.

Set up the inverter to charge from the AC input but I have left the PV isolated as I am still not sure if the readings at the input terminals are an issue.

Timer came to start and ac started charging the batteries at 10 amps (I have set this limit), mains in house not tripped and still charging as I type.

Not sure why there is no reading on the two cables (black and Blue) as the meter is showing 00.1 when I touch the terminals together as a test.

I am going to let the inverter charge the batteries for the period I have set to see if it keeps going.

I hope the results are able to help and I look forward to hearing what you think is needed next.

As ever many thanks for the help.

Regards

Tonyboy

Click to expand...

These readings indicate the output N-E link is inside the Axpert box.

Tonyboy said:

Good Morning Marconi

I have carried out the requested tests. Multi- meter set on 200ohms lowest setting.

Measured between N and E on output terminals reading was 00.2 not very high.
The measurement between the two cables with output mcb on and output rcd off, no reading at all just the decimal point.

Set up the inverter to charge from the AC input but I have left the PV isolated as I am still not sure if the readings at the input terminals are an issue.

Timer came to start and ac started charging the batteries at 10 amps (I have set this limit), mains in house not tripped and still charging as I type.

Not sure why there is no reading on the two cables (black and Blue) as the meter is showing 00.1 when I touch the terminals together as a test.

I am going to let the inverter charge the batteries for the period I have set to see if it keeps going.

I hope the results are able to help and I look forward to hearing what you think is needed next.

As ever many thanks for the help.

Regards

Tonyboy

Click to expand...

Did axpert box enter bypass mode while charging battery from mains? If not sure send me picture of display.

marconi said:

What I am working up as a solution is a very fast ac changeover switch to connect the ac output socket to either the inverter or the incoming grid mains but never both. Would you be happy with the changeover which happens within a few cycles of the ac mains so should not be noticeable?

Click to expand...

Hello Marconi

I thank you for the reply.

I will admit straight away that I have no idea of what one of those does.

Would this be something I could fit into the cabinet local to the inverter and controls?
The speed at which it changes over to some extent does not matter as it will not interfere with any items powered by the solar as they will only be things that are used when I am using the pv/batteries to power them.

My idea in the beginning was to have a method by which to charge the batteries overnight from the grid supplying the inverter, acting as a battery charger.

I would not have any need for the ac to supply any of my solar outlets as they would not be used at this time.
If such a switch could provide power to the inverter and the inverter could charge the batteries (if needed) and only do this then I would be quite happy with it.

I am assuming the issue is currently that when the grid supply is activated on by the inverter, it both supplies the inverter and then on to the output of the cabinet via the RCD/MCB in the cabinet in bypass mode before the consumer unit for
the solar.

I will have no need for the supply to be bypassed to the consumer unit and if it was just available from the inverter/charger for the batteries that would be more than satisfactory. My solar outlets are for a small number of items in the home that I would prefer to power by pv and in general would only be used when I am in the home and thereby reduce my consumption of the grid supplied power. Fanciful I guess but it was the premise of the initial purchase.

Please feel free to send me more information as and when you are able. I am off to work fairly soon and I will probably not be able to respond until late tomorrow or Friday late afternoon.

I am as ever very grateful for you help

Regards

Tonyboy

marconi said:

Did axpert box enter bypass mode while charging battery from mains? If not sure send me picture of display.

Click to expand...

Hello Marconi
have attached this, currently not charging as batteries are nearly full.

Regards

Tonyboy