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

The switching inside the inverter box is normally done by solid state switches to ensure no-break of supply when moving between mains to output or inverter to output.

Tonyboy - where have you happened upon the term TN-S? I suspect what you have bought or set up is an off grid systemwith genie back up to the inverter mains input. This would require the inverter output to be made tn-s in order for automatic disconnection of the inverter supply to the output socket in the event of an earth fault. This would be done on the inverter output. For uk mains input in lieu of genie one cannot link the output N with Cpc/earth/pe for the reason I mentioned earlier.

marconi said:

The switching inside the inverter box is normally done by solid state switches to ensure no-break of supply when moving between mains to output or inverter to output.

Tonyboy - where have you happened upon the term TN-S? I suspect what you have bought or set up is an off grid input with genie back up to the inverter mains input. This would require the inverter output to be made tn-s in order for automatic disconnection of the inverter supply to the output socket in the event of an earth fault. This would be done on the inverter output. For uk mains input in lieu of genie one cannot link the output N with Cpc/earth/pe for the reason I mentioned earlier.

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Hi Marconi
The description of the inverter outputs says it has a TN-S arrangement and when I purchased it I was told it was suitable to connect the mains as a standby/ additional source of charging power for overnight cheap rate electric.
It is indeed an off grid solar supplied unit with either standby genie or mains power to charge the batteries overnight.
Is there a solution to the issue of the cabinet being TN-S and does it involve changing or adding anything else to the system to rectify the issue. Currently I am having an issue with the inverter showing an F12 fault so I think that it will be going back to the supplier next week, however given they are selling this unit with the specific option of direct connection to a mains supply I had really expected it to work once it was connected.
I am content to change things if it will sort the problem but I don't want to be having to alter stuff in the cabinet as it is all pre wired and supposedly plug and play.
Many thanks again

tonyboy

Please see attached electrical art. Please study and note my remarks beside the three balloons. The ohmmeter tests at A, B,C and D must be done with all sources of electrical energy ie mains, battery and pv panels isolated. With ohmmeter set to low range eg 0 to 200 measure between N and E/cpc and tell me results.

marconi said:

Please see attached electrical art. Please study and note my remarks beside the three balloons. The ohmmeter tests at A, B,C and D must be done with all sources of electrical energy ie mains, battery and pv panels isolated. With ohmmeter set to low range eg 0 to 200 measure between N and E/cpc and tell me results.

Click to expand...

Hi Marconi
I think this will take me some time to do, as I will need to get access to the mains in my house and I am assuming the insides of the cabinet trunking and connections. To be honest it may be more than difficult to start dismantling the internal components of the cabinet as its all concealed, I will get in the cabinet and see what I can access and hopefully get back to you soon, I am working over the next three days on odd shifts so it may not be until the weekend or Monday.
I am assuming I is the inverter and the consumer unit on the right is my solar out unit.
Thanks for taking the time to do the drawing, I am very grateful.
My fears at present are that I am going to have to do some serious alterations to the set up and that was why I got a self contained cabinet to avoid this.

Quick edit I measured the point (b and c) before and after the rcd and got 00.2 for both and the consumer unit (D) with feed unplugged and all both on and off and got no reading. The main consumer unit is in a built in cupboard over the door and will take some getting to, so it may take me a while to get reading A.

We will see.
Regards

Tonyboy

What literature do you have that you can send me or a link to? Do you have a circuit diagram for the cabinet?

If your cabinet has on one side as in the earlier video clip two c forms for mains in and inverter out then I can spell out a way to do the measurements at the socket or plug N and E pins without dismantling anything. But that will be tomorrow because I am starting to cook for visitors tonight.

marconi said:

What literature do you have that you can send me or a link to? Do you have a circuit diagram for the cabinet?

If your cabinet has on one side as in the earlier video clip two c forms for mains in and inverter out then I can spell out a way to do the measurements at the socket or plug N and E pins without dismantling anything. But that will be tomorrow because I am starting to cook for visitors tonight.

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Hi Marconi

I have done a couple of measurements but would be appreciative of a spelt out instruction, being a heating engineer and all. I have attached a picture of the cabinet and it looks like the inside of mine pretty much albeit they send it with a different inverter.

I have been trying to get any kind of information about my cabinet with little success from the supplier I can't even get test results of the product before it was shipped to me, It is a shame because to be honest the product does not seem too bad.

I realise you and others have lives outside of the forum and I am very grateful of the help and advice I have received, I am working for the next three days all over the place so I might be able to get back to you in the evening this week.
I hope your evening meal goes well.
Regards and thanks

Tonyboy

Thank you for image of inside. I ought to be able to fathom out the wiring diagram from it.

marconi said:

Thank you for image of inside. I ought to be able to fathom out the wiring diagram from it.

Click to expand...

I will try to get a pic of my actual cabinet and send that later, then at least it will be the actual item.

find attached mine.

regards

Tonyboy

Thank you for the readings at B and C which indicate that N and E are connected together at the output side of the inverter to create a TN-S earthing system. (Just to confirm I assume you are on the lowest Ohms range and 00.2 is 00.2 Ohms ie less than 1 Ohm. To be sure what reading do you get when you connect the Ohmmeter probes together? ).

The reading at A can be done at the cabinet - you do not need to gain access to your home's main consumer unit.

Again, with all PV and battery and mains isolators opened and the plug and socket on the side of the cabinet removed, take your Ohmmeter on the lowest Ohms range and do a) and then b) below:

a) To gain access to the ingoing E put a probe on the earth terminal of the cform plug. To gain access to the ingoing N, go to the AC in C40 MCB, turn it on and put the other probe into its N terminal. This measures between N and E at the input to the inverter.

b) Now would you keep the probe on the ingoing N at the C40MCB and put the other probe on the N of the outgoing RCD - this RCD to be switched on. If there is a mains input on/off switch on the inverter box then these needs to be turned on for this measurement and off for a). This measures between input N and output N.

What are these two readings please?


Please tell me the part number of the output 40A ABB RCD or post a closer picture of its front - I want to see if it is single of double pole.

marconi said:

Thank you for the readings at B and C which indicate that N and E are connected together at the output side of the inverter to create a TN-S earthing system. (Just to confirm I assume you are on the lowest Ohms range and 00.2 is 00.2 Ohms ie less than 1 Ohm. To be sure what reading do you get when you connect the Ohmmeter probes together? ).

The reading at A can be done at the cabinet - you do not need to gain access to your home's main consumer unit.

Again, with all PV and battery and mains isolators opened and the plug and socket on the side of the cabinet removed, take your Ohmmeter on the lowest Ohms range and do a) and then b) below:

a) To gain access to the ingoing E put a probe on the earth terminal of the cform plug. To gain access to the ingoing N, go to the AC in C40 MCB, turn it on and put the other probe into its N terminal. This measures between N and E at the input to the inverter.

b) Now would you keep the probe on the ingoing N at the C40MCB and put the other probe on the N of the outgoing RCD - this RCD to be switched on. If there is a mains input on/off switch on the inverter box then these needs to be turned on for this measurement and off for a). This measures between input N and output N.

What are these two readings please?


Please tell me the part number of the output 40A ABB RCD or post a closer picture of its front - I want to see if it is single of double pole.

Click to expand...

Hello Marconi
Thanks for the guide and for taking the time to help me.
Just as a double check the reading on the meter with the 2 probes together was 00.1 and 00.2
The earth on the plug to incoming N, I had no reading
The N on the incoming C40 mcb to N on the outgoing RCD no reading.
I have also attached a pic of the output Rcd as requested.

The cabinet does not have a main on off other than the Inverter switch, the input is cut of on the rcd/mcb and before that is a soft start relay that unless powered stays off. I have installed a double pole ac Isolator outside of the cabinet and for the solar input I have a double pole switch also.

I am still a bit in the dark about the earthing of the system in this respect. I realise the ecl device in my home supply unit senses the earth leakage caused by my powering the mains on to the cabinet and I can see that if the cabinet did not have an RCD, this I assume would stop the issue occurring. (or maybe not) I see also the need for an rdc on the solar output to protect anyone using the appliances supplied from the cabinet. However If the solar supply in the consumer unit was earthed to a ground rod would this be suitable as a means of earth protection for the solar output. And if this was the case would it then be possible to remove the rcd from the solar cabinet output.
I think someone else commented that the solar output should have its own source of earth separate from the dno in case of power failure in that if the L and N were disconnected so would the earth back to my consumer unit be as it is joined to the N of the house input.
I am sure there are like all things a multitude of reasons for and against different options and I am hoping that there is a reasonably simple solution to my issue. I am however somewhat disappointed that having purchased a plug and play unit that is sold as such I am in the situation I am now in.
Research was my topic for 4 months before I committed to get the kit and at no point did the provider mention I may have some issue with my supply to the cabinet. I am not pointing the finger at anyone as at the end of the day I purchased the whole thing, but it sure would have helped if I had been given a heads up.

If my measurements have not provided any answers I am happy to check and test as much as you wish if it will help.
I am as ever very grateful for the help.
Regards
Tony

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