Automatic / Relay: Neutral Bonding?

[RabidBunny]

Please bear with me, as I am no artist, but at-least I am trying (for easier understanding I have separated the E/L/N diagrams - and they may not be 100% correct against termanology, but this is just to show the connecting dots) ...

 

Setup:

2x 8kW Deye Hybrid Inverters (linked in parallel), with battery bank and PV arrays.

 

I am sitting with a floating neutral problem, only when my system is in "off-grid" (ISLAND mode), when Eskom decides to pull the plug. When normal AC is returned, the floating neutral is resolved, due to proper connection between N and E.

Below is a sketch of my setup/wiring that may give some idea of how things are configured. I will most likely need to install a N/E bond relay that will trigger the bond to be established between N and E, when in "off-grid" (ISLAND mode) ~ for most parts I am running "off-grid", however when weather is terrible and I barely cope with PV, then I lend a little from Eskom.

1.      L/N + E is fed in

2.      L/N (input) runs through the “Surge Protector”, to protect everything down-stream

3.      L (input) is bridged to the “MAINS” circuit breaker, which in turn sends L (output) to both the inverters

4.      N (output) is linked to a common neutral (bar), which in turn sends N to both inverters

5.      E (output) from the “Surge Protector” is linked to fed-in E

6.      Since both inverters are “grounded” with the fed-in ground via the load, the circuit is complete – however when Eskom falls away, this is where my floating neutral occurs, this I assume is because the circuit cannot be completed to the main N being fed-in

My questions are:

1.      Where in this diagram would be the best placement for the “ground” and “neutral” bond / relay to be installed?

2.      Which relay would you advise I use for such a configuration?

3.      Since the setup is run in parallel, how will I configured the "bonding" for the second inverter? (both run on the same N + E)

4.      Do I need to replicate the "bonding" for the second inverter? (both run on the same N + E)

 

 

 

 

Edited October 19, 2021 by RabidBunny

[RWI]

Hi,  I have the same setup with two Deye 8 Kw in parallel.

You need to connect the N of the Inverter load output to your N bar.  When you are grid connected this is the N passed through to the load.  Hence the N is identical when you lose the grid and you are not floating. The only problem with this is if you isolate the incoming neutral from the neutral bar with for instance a 2 pole incoming breaker that you open for maintenance then you are floating again if you are operating in island mode. If this is possible then one option is a local E system with earth stakes and link this E bar to the N bar (normally you would have your own earth system).  If you don't have an earth system are are certain that the E from the supply is good and never disconnected then you could connect this to your N bar which is referred to as a MEN (multiple earth to neutral) system.  

Hope that this helps. Of course you need to check your local regulations for compliance but these usually do not envisage a potential isolated internal solar generation system.  The Deye inverters do have an output to operate a relay in island mode that you use to connect the N of the inverter load to E but of course this is an active and not a passive system and less reliable.  

 

[PowerUser]

31 minutes ago, RWI said:

Hi,  I have the same setup with two Deye 8 Kw in parallel.

You need to connect the N of the Inverter load output to your N bar.  When you are grid connected this is the N passed through to the load. 

 

As far as I know, this is not legal as per SANS and won't pass COC, if checked properly. You have to have a split Neutral with an inverter:

[RabidBunny]

I found an online editor (ERD), which I used to generate a graph depicting part of my setup, I'm not sure if this will make more sense than the above?

 

Note that both inverters are earthed with the LOAD (to the right thereof), which is in turn connected to the common earth.

 

When Eskom drops out, both inverters go into ISLAND mode and the L & N is cut between Eskom and the changeover, causing the floating neutral.

 

1. I assume that I may need to run a earth wire for both inverters back to the common earth and not "piggy-back" on the earth of the LOAD (to the right thereof)?

 

2. Once completed, I could possibly then install the earth/neutral bond relay (at the now new common feed for both neutral and earth just after exiting the inverters)?

 

The only reason I need to do this is because 95% of the month, I am running in complete ISLAND mode and only switch back to Eskom when the weather is really horrible.

 

I plan to completely phase out the other 5% as well, by connecting the generator with auto-start signaling when PV generation is seriously struggling, but until such a time that I am 100% in ISLAND mode I cannot hard-wire the earth and neutral bond, and it makes me feel uneasy having the floating neutral issue when Eskom does drop-off.

 

Edited October 21, 2021 by RabidBunny

[RWI]

I am not directly familiar with your system but I believe that South Africa implements the Terre-Neutral-Combined-Separated earthing system TNC-S in which the neutral and protective earth conductors are combined on the utility side but separated on the customer side (see attached).  Your diagrams appear to confirm this.

If this is the case then you probably don't have your own earth system with earth stakes and all earths are connected to the incoming supply earth only.  Hence if you install a relay to connect N to E on the islanded load side of the inverters you are in fact connecting the Ns together through the earth system.  It would be the same situation on the diagram provided by PowerUser unless you wanted the UPS power to be floating.

In some similar TNC-S systems such as Australia and NZ they have a MEN (multiple earth to neutral) addition where a local earth system can also be connected to the neutral giving multiple earth to neutral connections.

I had a quick look at your standards to see if there was anything on solar systems and it appears that this is in draft from at the moment.  I have however attached the diagrams from the draft which show the neutrals all connected together.

Hope that this is of some help.

[BritishRacingGreen]

I have ittle knowledge of official COC standards and best-effort recommendations .So I can only apply first principle logic here. I see this neutral to earth bonding issue appear from time to time on forum threads. 

For me proper earth leakage detection is of utmost importance to protect lives in my home as well as equipment. To ensure this I need, inter alia,  neutral properly and securely bonded to earth before my earth leakage detector.

Any earth fault detected , will result in the ELD tripping . Being tripped , and being double poled ( i assume many if not all ELD) are double poled) the downstream neutral will not be earthed anymore and  will loose it's property as being a neutral. However since there is no power on this circuit anymore, it bears no danger ( fail-to-safe) . 

For me , this means that any device downstream from the MCB or ELD  that is re-generating energy, cannot rely on the Neatral to be at earth potential anymore ( MCB or ELD could be tripped) .  Logic then states that a so called island or micro grid , must reconstruct all protective measures in the event of grid supply absent , in order for the island to conform to protection/safety requirements . This means that I need to hard bond a local earth to what is labbeled as the inverter neutral output , wether done by failsafe relay or other mechanism. 

Based on this , I would ideally love to wire my inverter  on the incoming side of mains , bypassing MCB and ELD , but I assume that one of the reasons for not doing so, is to protect the circuit  between mains and the inverter input.

Please correct me where my logic fails, hence the need for my post.

 

 

[RWI]

ELCBs are old type voltage devices and are not generally used now.  The safety protection devices used in domestic installations and other places today are RCD/RCCB and are current devices.  They measure the current difference between the two wires supplying the device and trip if this is more than a certain value typically 30 mA for domestic installations.  They will therefore work even if there is a high impedance between N and E (not good ground) and if there is no connection at all it is not technically unsafe if one wire is connected to ground unintentionally (fully floating system).  A good N to E connection is however required to trip on earth fault unless you have an IT system (very high impedance earth) used in parts of Europe.

The important thing is that if the system is designed for a hard connection between N and E then this is always maintained preferably by passive means and not relying on actuated devices.  

[Gerrie]

On 2021/10/21 at 10:38 PM, RabidBunny said:

When Eskom drops out, both inverters go into ISLAND mode and the L & N is cut between Eskom and the changeover, causing the floating neutral.

When Eskom drops out the bonding relay is supposed to switch on and create the bond. If you don’t have that bonding relay in place when there is a earth fault on a plug your earth leakage can not see the fault and will not trip. I suppose you don’t have to install two bonding relays but at least one on the master inverter and that should cover the bonding issue unless the master and slave’s output’s are separated and feeding different section in your DB then it might be better to install a bonding relay for each inverter.

[Gnome]

Never, EVER connect the neutral of two power sources to each other.  There is no country in the world where that is legal.

Neutral bonding means a relay that connects the neutral output of the inverter to the ground wire of your home.  The simplest way to do this is using a 220v coil SPDT relay.  The common connects to your ground and the Normally Closed (NC) connects to your neutral.  The relay coil is powered from your Utility power (ie. Eskom).  When the utility power cuts out the relay turns off and the normally closed and common terminal is connected.  Thus your ground and inverter neutral is "bonded".  When utility power comes back, the relay switches back on disconnecting them.

Note that this doesn't work perfectly because the inverter may switch at different times than the actual utility disconnecting.  So really the only way to do this in a complaint manner in pretty much every country in the world that requires it, is to have the relay switched by the inverter.  So when switching to inverter power, it powers a relay which bonds.

As to why this bond needs to be created:  Your home's ground wire is floating in respect to the inverter.  Meaning they are two different power sources and no way for current to flow between them.  Bonding creates a path.  There are different earthing systems.  South Africa implement many different kinds, there isn't just one kind in South Africa.  Some earthing systems have a stake driven into the ground at your installation.  Others have a ground wire coming from the utility. It is a complex subject.  Doesn't really change the fact that a bonding relay is required.  If you don't have a ground bond, your Earth Leakage doesn't work.  I mean apart from the fact that your installation becomes insanely dangerous

 

Edited October 24, 2021 by Gnome

[RWI]

This is a complex issue with many different opinions and experiences.  I do not intend to get into an esoteric discussion on this Forum.

[HannesZ]

This discussion was help full. Can anyone please suggest a Relay that I can use to connect the output of the inverters N to the earth when in Island mode as per https://www.sunsynk.org/post/automatic-neutral-earth-bond

 

I have found this https://www.acdc.co.za/pages/product-individual?JQX-50F 40VDC but as I have two 5.5K in parallel I would prefer a 63A 230VAC relay due to al the CB's being 63A to protect the wires. Preferably one that does not cost the sacrifice of my  first born son. I have grown fond of this one....

Edited October 27, 2021 by HannesZ

[PowerUser]

6 hours ago, HannesZ said:

This discussion was help full. Can anyone please suggest a Relay that I can use to connect the output of the inverters N to the earth when in Island mode as per https://www.sunsynk.org/post/automatic-neutral-earth-bond

 

I have found this https://www.acdc.co.za/pages/product-individual?JQX-50F 40VDC but as I have two 5.5K in parallel I would prefer a 63A 230VAC relay due to al the CB's being 63A to protect the wires. Preferably one that does not cost the sacrifice of my  first born son. I have grown fond of this one....

You don’t need 40A relay for that. 10A is enough. You can order a Weidmuller relay from Voltex:

https://www.voltex.co.za/product/weidmuller-d-series-220vac-10a-8-pin-relay-with-led-2-c0/
 

this model comes with or without LED - whatever suits you. Make sure, you order the base for it too. 
 

Running 2 inverters in parallel, I would assume, you only need to install one on the master. But rather confirm with someone familiar with parallel installations or ask SunSynk. 

Edited October 27, 2021 by PowerUser

[Gnome]

On 2021/10/27 at 2:09 PM, HannesZ said:

This discussion was help full. Can anyone please suggest a Relay that I can use to connect the output of the inverters N to the earth when in Island mode as per https://www.sunsynk.org/post/automatic-neutral-earth-bond

 

I have found this https://www.acdc.co.za/pages/product-individual?JQX-50F 40VDC but as I have two 5.5K in parallel I would prefer a 63A 230VAC relay due to al the CB's being 63A to protect the wires. Preferably one that does not cost the sacrifice of my  first born son. I have grown fond of this one....

I used one exactly like that.  Worked well until I got my new Axpert King which automatically does its ground thing.   But yeah the 63a is probably overkill

[RabidBunny]

Thanks for the replies everyone!

 

Summary:

I only have one earth/neutral bond at the meter-box (municipal); when the grid drops off - I lose the bond which causes a floating neutral (due to it not finding it's way back to earth).

 

Resolution:

I've proceeded to install an earth-spike close to the inverters and will soon be connecting it to a 4 pole contactor (2NO/2NC) that will establish the required bond (while the grid is dropped off).

 

Question:

Is there a way to "reverse" the ISLAND mode trigger?

I'm trying to only have the inverters send the ATS 230VAC signal (if the inverters are running on-grid); so that I can have the contactor "disconnect" the local inverter bond and rely on the meter-box (municipal) bond.

 

^ since I will only be "on-grid" once or twice a month; in order to extend the contactor life by not energizing it 99% of the times (when not needed).

Edited November 10, 2021 by RabidBunny

[Beat]

On 2021/10/24 at 5:50 PM, Gnome said:

Never, EVER connect the neutral of two power sources to each other.  There is no country in the world where that is legal.

I did exactly that. In order to save some 22m of 6mm² wire I pulled only one neutral and connected neutral in and out on my Axpert MKS 5K together. It worked well for now 1½ years. I see no technical reason why not. But I admit regulations are regulations, no matter how reasonable they are. So in order to conform with them I plan to pull in an additional wire.

That rises the question about earth bonding of the insulated inverter loads. I found out that this inverter has an earth feature built in. See schematic below. R are the relays that switch from battery (inverter) mode to utility bypass mode. That means no external measures needed. There is a removable screw that allows to disable that feature (see picture below). For my interconnected neutrals I had to take it out. I will have to put it back in. It is a pity that there is no documentation about it. It is even in contradiction with program setting 38. I do not know if other Voltronics models also do  have this feature. Mine is the MKS 5K built in April 2019 with firmware 74.40. It can be determined by ringing between the inverter neutral terminal and earth terminal when unit is disconnected and electrically dead.

Edited November 16, 2021 by Beat

[Gnome]

2 hours ago, Beat said:

I did exactly that. In order to save some 22m of 6mm² wire I pulled only one neutral and connected neutral in and out on my Axpert MKS 5K together.

I'm confused, do you not have an earth wire running to your inverter, is that what you are saying?

2 hours ago, Beat said:

 I pulled only one neutral and connected neutral in and out on my Axpert MKS 5K together.

Definitely not legal.

2 hours ago, Beat said:

But I admit regulations are regulations, no matter how reasonable they are

These regulations for inverter installs are pretty universal around the world.  Multiple engineers have thought this through and come up with a set of "rules" that they believe are important to follow.  Since they don't make extra money by having you NOT connect these two neutral conductors from different power sources together, let's assume they made that decision not because they wanted to make "rules" but instead because there are fundamentals involved that make it the right decision.

To challenge something like the regulations, you should start by first understanding WHY they made that decision.  Be able to explain it thoroughly and then through the process of rationalisation advocate for why it isn't relevant in your case.

That is the engineering way.

The YOLO way is, I don't understand it, but who cares, it didn't blow up right now.

Now I say the above with respect, if you want to do it differently, it isn't like I can stop you   I also don't care too much.  But recommending it to others would be where I would get offended.  That is how anti-vaxxing became a thing.

2 hours ago, Beat said:

That rises the question about earth bonding of the insulated inverter loads. I found out that this inverter has an earth feature built in. See schematic below. R are the relays that switch from battery (inverter) mode to utility bypass mode. That means no external measures needed. There is a removable screw that allows to disable that feature (see picture below). For my interconnected neutrals I had to take it out. I will have to put it back in

So if you probe between the inverter input neutral and output earth, is there continuity after you screw that in?

I'll admit I didn't know about that screw and this could be a very useful thing to know about!

Edited November 16, 2021 by Gnome

[KLEVA]

As per @Beatabove, I did exactly the same on my old Axpert 10kW, bugger the regulations. It worked and stopped any floating earth issue in my case.

The concern is more whether you can trust the the municipal N/E is actually earthed if you are "islanded". Despite being certified and knowledgeable with various SANS codes, and hearing all the rules and regulations, my personal thoughts are as follows:
* Ground/Earth your Municipal supply yourself (properly to make sure it is valid) as close as possible to your incoming supply (ie: Assume Municipality is unEarthed)
* Wire your Earth connections to that common point (before invertor so N & E are common throughout your home and to the invertor)
* Unless the Nuetral from the Municipality suddenly becomes live, this will stay a common ground/Earth, so bond the 2 together at that point.
* If the Municipal Earth becomes live for some wierd reason, then the Voltages will be in relatively minimal distances, or you will end up in a floating 110V. (In which case start fighting with them about reperation if stuff blows up!), but seriously the normal invertor would just shut off.
* Almost all invertors would have already switched over due to the bad incoming voltage and will switch back to "island" mode, so your local E & N would still be bonded, and isolate you.

Then at that point your E & N are completely common, any variance can be traced internally to devices and will still trip the 30mA limit on your DB.

This is the cheap and nasty solution, but also understand that whatever relay system you try put in place will still take a few milliseconds to kick in. Not just equipment damage can occur, but also severe 110VAC could go through something/someone in that time. My thoughts are to bond them permanently as close as you can to the municipal input and inverter output.

My personal thoughts are just bond the input and output N & E together unless your system hates it, but at least bond the output of the invertor always back to E.

*** DISCLAIMER: These are my thoughts, please test each step properly. What works for my previous setups might not be suitable for your situation and installation. A qualified Electrician locally should confirm or deny my logic, and you will need a CoC anyway. The above information is my personal thoughts and not a qualified recommendation, consultation with a local master electrician is still recommended.

[BritishRacingGreen]

4 hours ago, Gnome said:

I'm confused, do you not have an earth wire running to your inverter, is that what you are saying?

Definitely not legal.

These regulations for inverter installs are pretty universal around the world.  Multiple engineers have thought this through and come up with a set of "rules" that they believe are important to follow.  Since they don't make extra money by having you NOT connect these two neutral conductors from different power sources together, let's assume they made that decision not because they wanted to make "rules" but instead because there are fundamentals involved that make it the right decision.

To challenge something like the regulations, you should start by first understanding WHY they made that decision.  Be able to explain it thoroughly and then through the process of rationalisation advocate for why it isn't relevant in your case.

That is the engineering way.

The YOLO way is, I don't understand it, but who cares, it didn't blow up right now.

Now I say the above with respect, if you want to do it differently, it isn't like I can stop you   I also don't care too much.  But recommending it to others would be where I would get offended.  That is how anti-vaxxing became a thing.

So if you probe between the inverter input neutral and output earth, is there continuity after you screw that in?

I'll admit I didn't know about that screw and this could be a very useful thing to know about!

@Gnome I do not agree or disagree with you regarding the anti-vaxxing , but you are right on  the money with your technical  statements,  and I hope your message reaches the intended . Because earthing arrangements are not trivial , to say the least, in terms of equipment and human safety.

[Beat]

17 hours ago, Gnome said:

I'm confused, do you not have an earth wire running to your inverter, is that what you are saying?

Not at all. Of course I do have an earth wire from the DB to the inverter and connected to its earth terminal. That's why I found out about that earth screw. Initially I temporarily wired the  inverter downstream of the ELD and that tripped because of the neutral interconnection. I first thought that there was something wrong with the inverter wiring, opened it and finally found that screw below the microprocessor board. After I removed it ELD no longer tripped.

 

17 hours ago, Gnome said:

So if you probe between the inverter input neutral and output earth, is there continuity after you screw that in?

No, you probe continuity between inverter output neutral and earth when unit is electrically dead. That screw is factory installed.

Edited November 17, 2021 by Beat

[Gnome]

9 minutes ago, Beat said:

Not at all. Of course I do have an earth wire from the DB to the inverter and connected to its earth terminal. That's why I found out about that earth screw. Initially I temporarily wired the  inverter downstream of the ELD and that tripped because of the neutral interconnection. I first thought that there was something wrong with the inverter wiring, opened it and finally found that screw below the microprocessor board. After I removed it ELD no longer tripped.

 

No, you probe continuity between inverter output neutral and earth when unit is electrically dead. That screw is factory installed.

Ah ok good to hear, but then you wouldn't have needed to run an extra wire.  As long as you have an earth wire running to your inverter you can just put a relay that would close when it is powered down to connect output neutral and earth.  Also BTW. you don't need to run 6mm.  If your supply wire is 6mm your earth wire can be 2.5mm.  The regulations allow a reduction in size of the earth conductor.  The best guide is to check what the size of the equivalent earth conductor is in twin and earth or surfix cable.  In both 6mm have a 2.5mm earth wire.

9 minutes ago, Beat said:

No, you probe continuity between inverter output neutral and earth when unit is electrically dead. That screw is factory installed.

Ah man, I meant to say output neutral.  Nice discovery!  This is super valuable info.  I had no idea this existed and I wish I did before for another install.  Thanks!

[Beat]

13 minutes ago, Gnome said:

Ah ok good to hear, but then you wouldn't have needed to run an extra wire.  As long as you have an earth wire running to your inverter you can just put a relay that would close when it is powered down to connect output neutral and earth.  Also BTW. you don't need to run 6mm.  If your supply wire is 6mm your earth wire can be 2.5mm.

That's what I did, earth wire is 2.5mm². No extra wire, just 6mm² each for phase in and phase out and also for neutral. So I will add another 6mm² neutral wire to separate utility neutral from inverter neutral. No need for a relay since that bonding is done with the internal earth screw.

25 minutes ago, Gnome said:

  Nice discovery!  This is super valuable info.  I had no idea this existed and I wish I did before for another install.  Thanks!

Yeh, as I wrote it's a pity that this is not documented. The setting 38 instructions are even totally misleading on the matter.

[Gnome]

1 hour ago, Beat said:

That's what I did, earth wire is 2.5mm². No extra wire, just 6mm² each for phase in and phase out and also for neutral. So I will add another 6mm² neutral wire to separate utility neutral from inverter neutral. No need for a relay since that bonding is done with the internal earth screw.

Aaah ok, now I get it.  Yeah def. best to install that, especially if you want a CoC

[Coulomb]

On 2021/11/16 at 11:45 PM, Beat said:

See schematic below. R are the relays that switch from battery (inverter) mode to utility bypass mode.

In my experience, Axperts with the automatic connection of AC-out N to earth are wired like this:

Note three single throw relays (some models have only 2), and one double throw relay. The extra throw contact is the connection from AC-out neutral to earth when the "safety" relay is off (battery mode). So AC-out neutral gets its earth either from that connection, or from the incoming neutral (either at the transformer, or at the main distribution board).

You do have the double throw relay:

Note how the writing on that relay is different to the others.

All models after about 2016 seem to have this extra contact on that relay.

On 2021/11/16 at 11:45 PM, Beat said:

There is a removable screw that allows to disable that feature (see picture below).

I don't believe that the screw is designed to make that feature optional. There are other screws with the same graphic. I suspect that those small blue capacitors near that screw use that screw to conduct switching transients to earth.

On 2021/11/16 at 11:45 PM, Beat said:

It is even in contradiction with program setting 38.

Setting 38 is about the function of the clean contact relay. I agree that it makes little sense to have that setting when the inverter does that function for you. Setting 38 is missing in many firmwares, for example in Axpert Kings.

[Beat]

2 hours ago, Coulomb said:

In my experience, Axperts with the automatic connection of AC-out N to earth are wired like this:

Thank you Coulomb for your precision and confirmation. I was expecting you to comment with your knowledge. My schematic is a simplification but functionally almost the same.

Yes I have seen that double trow relay, that's why I came to my conclusion. It's interesting that Voltronic inverters have that feature since 2016 but no documentation tells about it. It could have saved headaches and costs to many peoples that are looking for a neutral earth bonding solution. I firmly believe that this unique screw with its symbols printed on the board is meant to be removable to inactivate that feature when required. Anyway for normal application it should remain in place and serve for the automatic inverter neutral to earth bonding.

Concerning setting 38: I just only now checked on my remote panel and found out that this setting is not available in my firmware 74.40.

Edited November 17, 2021 by Beat

[Coulomb]

On 2021/11/18 at 2:58 AM, Beat said:

It's interesting that Voltronic inverters have that feature since 2016 but no documentation tells about it. It could have saved headaches and costs

I think that the general lack of proper documentation is appalling. But that's what you get with Axpert level price. For Victron-level price you expect more.

On 2021/11/18 at 2:58 AM, Beat said:

I firmly believe that this unique screw with its symbols printed on the board is meant to be removable to inactivate that feature when required.

On the only main  board to hand, from about 2013, I see three holes with the screw and earth-in-a-circle symbols near them. Including on the equivalent screw hole near the relays. But indeed this one has no copper pad under the board, so that removing that screw would indeed inactivate that relay, though also some EMI suppression I suspect.

On 2021/11/18 at 2:58 AM, Beat said:

found out that this setting is not available in my firmware 74.40.

Well, I guess that makes sense, at least.

[ Edit: trace -> copper pad ]

Edited June 27, 2022 by Coulomb