Hi

I have a issue with two axpert Max 1 8Kw (parrallel configuration).

My grid residual current breaker (500ma 63A) trip when the two inverter return to grid mode and i don't know why (on battery mode no problems).

Each inverter grid input is protected by a 300ma 16A residual current breaker (that is required for transformerless inverters that don't have galvanic isolation) and a 16A current breaker. The two 16A residual breakers also trip when the inverter return to grid mode (but no the two classic 16A breakers).

The earth of each inverter is wired from grid earth (no separate earth).

Someone have an idea of where is the problem ? The inverters are too big for the breakers ? A faulty earth ? Grid power is too low ?

Any help will be very appreciated 🙏

Best Regards

Francis

On 2026/03/11 at 8:55 AM, fhocorp said:

Each inverter grid input is protected by a 300ma 16A residual current breaker (that is required for transformerless inverters that don't have galvanic isolation) and a 16A current breaker.

Are you saying that each inverter's grid input has a residual current breaker in series with a classic breaker?

Or is the classic breaker on the inverters' outputs (heading to the loads)?

16A seems marginal for an 8kW inverter, especially on the AC input, where you might have 8kW of loads plus several kilowatts of AC charging. That could explain the 16A RCDs breaking, and that might somehow cause the 63A breaker to trip.

I'll grant you that this is a long shot.

It might be worth replacing the bypass relays (contactors?) in one of the inverters to see if that helps. Perhaps just the neutral changeover relay, as that switches earth to the inverter's neutral output. If that is slow or arcing or stuck, it might cause current imbalances that trip the RCDs.

Also check the earth and neutral wiring of the premesis carefully. Just a little neutral current carried by an earth wire somewhere will unbalance active and neutral currents and cause RCDs to trip.

Edit: Also check for screws missing on the main boards near these bypass relays. The earth connection to the changeover neutral relay usually goes through a hex screw and its threaded standoff, via the metalwork to the inverter's earth terminal.

Edited March 15Mar 15 by Coulomb

On 2026/03/15 at 5:18 AM, Coulomb said:

Are you saying that each inverter's grid input has a residual current breaker in series with a classic breaker?

Or is the classic breaker on the inverters' outputs (heading to the loads)?

16A seems marginal for an 8kW inverter, especially on the AC input, where you might have 8kW of loads plus several kilowatts of AC charging. That could explain the 16A RCDs breaking, and that might somehow cause the 63A breaker to trip.

I'll grant you that this is a long shot.

It might be worth replacing the bypass relays (contactors?) in one of the inverters to see if that helps. Perhaps just the neutral changeover relay, as that switches earth to the inverter's neutral output. If that is slow or arcing or stuck, it might cause current imbalances that trip the RCDs.

Also check the earth and neutral wiring of the premesis carefully. Just a little neutral current carried by an earth wire somewhere will unbalance active and neutral currents and cause RCDs to trip.

Edit: Also check for screws missing on the main boards near these bypass relays. The earth connection to the changeover neutral relay usually goes through a hex screw and its threaded standoff, via the metalwork to the inverter's earth terminal.

Hi @Coulomb thanks for your reply.

On 2026/03/15 at 5:18 AM, Coulomb said:

Are you saying that each inverter's grid input has a residual current breaker in series with a classic breaker?

Yes, it is like that.

On 2026/03/15 at 5:18 AM, Coulomb said:

Or is the classic breaker on the inverters' outputs (heading to the loads)?

I have also a 63A residual breaker for AC outpout, it is placed after the two C32A classic breaker for each inverter outpout ( i get inspired by your setup)

On 2026/03/15 at 5:18 AM, Coulomb said:

16A seems marginal for an 8kW inverter, especially on the AC input, where you might have 8kW of loads plus several kilowatts of AC charging. That could explain the 16A RCDs breaking, and that might somehow cause the 63A breaker to trip.

Yes, your are right. I am waiting for my 2 RCD Type B 40A residual breaker. Since my inverter never charges the batteries from the mains grid (execpted in emergency case when also my gasoline group is also used for charging) the main grid usage never get more that 20A in classical situations. I have choosen the 40A caliburn just for safety. I will never use 63A breaker for main input because my 6mm2 input cable could'nt handle it.

On 2026/03/15 at 5:18 AM, Coulomb said:

It might be worth replacing the bypass relays (contactors?) in one of the inverters to see if that helps. Perhaps just the neutral changeover relay, as that switches earth to the inverter's neutral output. If that is slow or arcing or stuck, it might cause current imbalances that trip the RCDs.

When the inverter where installed, i have reversed the fans and check for the relays and i don't find any issue like that. Also the screws for neutral to earth and they are in place.

Each inverter AC output is wired in 6mm2.

Maybe a faulty breaker or like you said, a undersized breaker. But that doesn't explain why the grid main AC breaker of the house that are 120A sized is tripping...

Thanks for your help

Best Regards

Hi

I received my 40A Type B residual breakers this week.

I have installed them, and tried a bypass mode to grid. The new breakers triped.

My 2 axpert max inverters get to much power when going to grid mode ?

Little precision : i am in triphased in my grid installation, but i can't use all the phases due to technical issues so the inverters input is only on one phase. Since i have 12Kva in triphased, i could have only 20A max per phase. How much the axpert max handle at startup at grid mode ?

My old 5Kva axpert King inverters doesn't have to much issue with grid. There is a way to reinstall a 5Kva with it's output dirrectly connected to the axpert max grid input (and of course it's grid input to the grid breakers) ?

I suspect that my grid installation doesn't support the axpert max. Actually, the only way to connect my max to the grid is this way :

• Completely shutdown inverters

• Disconnect PV input and grid input

• Startup the 2 inverters

• Connect the grid input

• Wait for the inverters to connect to grid

• Connect the PV inputs

But even with this method, the breakers trip.

Any ideas @Youda ? 😕

The new breakers pictures are in attachements

4 hours ago, fhocorp said:

Hi

I received my 40A Type B residual breakers this week.

I have installed them, and tried a bypass mode to grid. The new breakers triped.

My 2 axpert max inverters get to much power when going to grid mode ?

Little precision : i am in triphased in my grid installation, but i can't use all the phases due to technical issues so the inverters input is only on one phase. Since i have 12Kva in triphased, i could have only 20A max per phase. How much the axpert max handle at startup at grid mode ?

My old 5Kva axpert King inverters doesn't have to much issue with grid. There is a way to reinstall a 5Kva with it's output dirrectly connected to the axpert max grid input (and of course it's grid input to the grid breakers) ?

I suspect that my grid installation doesn't support the axpert max. Actually, the only way to connect my max to the grid is this way :

• Completely shutdown inverters

• Disconnect PV input and grid input

• Startup the 2 inverters

• Connect the grid input

• Wait for the inverters to connect to grid

• Connect the PV inputs

But even with this method, the breakers trip.

Any ideas @Youda ? 😕

The new breakers pictures are in attachements

When tripping g a 120A MCB on the AC supply to the house you have a serious problem.

The new residual breakers could be tripping on a short or an earth fault current.

The whole installation should be checked out. It does not seem we have any clues what you can do

This is a classic of one need to test and have measurement in order to be guided in the right direction.

50 minutes ago, Scorp007 said:

When tripping g a 120A MCB on the AC supply to the house you have a serious problem.

The new residual breakers could be tripping on a short or an earth fault current.

The whole installation should be checked out. It does not seem we have any clues what you can do

This is a classic of one need to test and have measurement in order to be guided in the right direction.

Yes, it is possible. The earth is not good on the house, i am in location and the owners don't want to repair the installation so...i am embarrasted like that...

That does't explain why a 5Kw is working and a 8Kw not. The length and the size is a criteria for the issue ?

Best Regards

18 minutes ago, fhocorp said:

Yes, it is possible. The earth is not good on the house, i am in location and the owners don't want to repair the installation so...i am embarrasted like that...

That does't explain why a 5Kw is working and a 8Kw not. The length and the size is a criteria for the issue ?

Best Regards

I doubt it is related to the size. Bad earthing to me would just mean very unsafe and human can be electrocuted when touching a live wire.

On your point by point around switching do you get tripping before switching on any loads?

Hi Francis @fhocorp ,Thanks for the latest update and for addressing @Scorp007 point directly. You’re correct to highlight the key question: why does the older 5 kW Axpert King handle the grid reconnection without tripping the RCDs, while the parallel pair of 8 kW Axpert Max units cause significant leakage trips even tripping the main 120 A breaker? And whether cable length and size play a role. Why the 5 kW King behaves better than the 8 kW Max in parallel This difference is common and not surprising for these Voltronic models.

• The Axpert King 5 kW is generally a bit gentler on the grid reconnection. Its internal relays, control logic, and neutral earth bonding changeover are tuned differently often with slightly slower or smoother timing. Many users report that the King series has fewer nuisance RCD trips during bypass switching compared to the Max series.

• The Axpert Max 8 kW has a higher power rating, larger internal components, and different firmware behaviour. When two units run in parallel, they must synchronise their relays almost perfectly. Even a small mismatch in relay timing a few milliseconds between the master and slave can create a larger neutral-earth current pulse during the changeover. The higher power capability also means any transient imbalance can involve more current, making the leakage spike bigger and more likely to trip sensitive or even 40 A Type B RCDs and upstream breakers.

• It’s not necessarily that the 8 kW is faulty, but the parallel combination plus higher power amplifies the exact transient that the single 5 kW King can hide more easily. Your poor house earth as you mentioned makes the system even more sensitive to any earth current spike.

Is cable length and size a factor? Yes, it can contribute, but it is usually secondary, not the main cause.

• Longer or undersized cables on the grid input side increase impedance. This can make the voltage sag or the inrush current spike during reconnection slightly worse, which in turn can stress the relays and increase the chance of arcing or imperfect neutral switching means a bigger leakage pulse.

• Your earlier mention of 6 mm2 cable and low grid charging max 20 A per phase on a single phase setup suggests the cables may be marginal when the two 8 kW units try to connect simultaneously. The 5 kW King draws less peak current on reconnection, so the same cables cope better with it.

• However, if the magnetic breakers never trip, the issue is still primarily the short duration residual (leakage) current, not sustained overcurrent. Cable length and size would mainly affect the severity of the transient rather than create it from nothing.

Recommendations considering the latest points given the poor house earth and the clear difference between 5 kW King and 8 kW Max.

1. Do the temporary bypass test on the 40 A Type B RCDs as suggested before. This will quickly tell us whether the pulse is so large that it affects the main breakers even without the input RCDs.

2. Try the King buffering idea you mentioned feed the grid input of the two Max 8 kW units from the output or a spare grid passthrough of one 5 kW King. Let the King connect to the main grid first. Many users find this smooths the transition dramatically because the Max units then see a more stable source.

3. Address the earth quality even if the owners don’t want major repairs, a local electrician could at least improve the earth connection at your distribution board or add a temporary supplementary earth rod for testing. A high earth impedance makes every leakage pulse worse.

4. Consider S type time delayed RCDs on the grid inputs to the Max pair 100 mA or 300 mA S type. This is still the most common successful fix for Max parallel reconnection trips.

5. Cable check If the input cables to the two Max units are significantly longer or different in length from each other, try to make them as short and symmetrical as possible. Upgrading to thicker cable 10 mm2 on the grid input side could reduce any contribution from impedance, especially if you ever draw more grid current.

If the bypass test or King buffering still shows trips on the main breakers, then the combination of poor earth plus large parallel transient may require a proper on site measurement of leakage current during the switch with a clamp meter that reads mA.This explains the 5 kW vs 8 kW difference quite well it’s the combination of parallel operation, higher power, and the specific relay behaviour of the Max series, made worse by marginal cables and weak earthing.Please keep us posted on the results of the bypass test or the King buffering attempt. If you can also note the approximate cable lengths and sizes to each inverter, that would help refine the advice further.
PowerForum Store

46 minutes ago, Scorp007 said:

I doubt it is related to the size. Bad earthing to me would just mean very unsafe and human can be electrocuted when touching a live wire.

On your point by point around switching do you get tripping before switching on any loads?

Hi thanks for your answer. Yes, tripping happen when inverter switch to grid mode, when no load on it. One of the inverters even show a F09 error that could be solved by restarting completely the inverter (disconnect loads, battery and grid).

The input grid wire is 2,5mm3. Replacement to 6mm3 is planned next month

1 hour ago, Powerforum Store said:

Hi Francis @fhocorp ,Thanks for the latest update and for addressing @Scorp007 point directly. You’re correct to highlight the key question: why does the older 5 kW Axpert King handle the grid reconnection without tripping the RCDs, while the parallel pair of 8 kW Axpert Max units cause significant leakage trips even tripping the main 120 A breaker? And whether cable length and size play a role. Why the 5 kW King behaves better than the 8 kW Max in parallel This difference is common and not surprising for these Voltronic models.

• The Axpert King 5 kW is generally a bit gentler on the grid reconnection. Its internal relays, control logic, and neutral earth bonding changeover are tuned differently often with slightly slower or smoother timing. Many users report that the King series has fewer nuisance RCD trips during bypass switching compared to the Max series.

• The Axpert Max 8 kW has a higher power rating, larger internal components, and different firmware behaviour. When two units run in parallel, they must synchronise their relays almost perfectly. Even a small mismatch in relay timing a few milliseconds between the master and slave can create a larger neutral-earth current pulse during the changeover. The higher power capability also means any transient imbalance can involve more current, making the leakage spike bigger and more likely to trip sensitive or even 40 A Type B RCDs and upstream breakers.

• It’s not necessarily that the 8 kW is faulty, but the parallel combination plus higher power amplifies the exact transient that the single 5 kW King can hide more easily. Your poor house earth as you mentioned makes the system even more sensitive to any earth current spike.

Is cable length and size a factor? Yes, it can contribute, but it is usually secondary, not the main cause.

• Longer or undersized cables on the grid input side increase impedance. This can make the voltage sag or the inrush current spike during reconnection slightly worse, which in turn can stress the relays and increase the chance of arcing or imperfect neutral switching means a bigger leakage pulse.

• Your earlier mention of 6 mm2 cable and low grid charging max 20 A per phase on a single phase setup suggests the cables may be marginal when the two 8 kW units try to connect simultaneously. The 5 kW King draws less peak current on reconnection, so the same cables cope better with it.

• However, if the magnetic breakers never trip, the issue is still primarily the short duration residual (leakage) current, not sustained overcurrent. Cable length and size would mainly affect the severity of the transient rather than create it from nothing.

Recommendations considering the latest points given the poor house earth and the clear difference between 5 kW King and 8 kW Max.

1. Do the temporary bypass test on the 40 A Type B RCDs as suggested before. This will quickly tell us whether the pulse is so large that it affects the main breakers even without the input RCDs.

2. Try the King buffering idea you mentioned feed the grid input of the two Max 8 kW units from the output or a spare grid passthrough of one 5 kW King. Let the King connect to the main grid first. Many users find this smooths the transition dramatically because the Max units then see a more stable source.

3. Address the earth quality even if the owners don’t want major repairs, a local electrician could at least improve the earth connection at your distribution board or add a temporary supplementary earth rod for testing. A high earth impedance makes every leakage pulse worse.

4. Consider S type time delayed RCDs on the grid inputs to the Max pair 100 mA or 300 mA S type. This is still the most common successful fix for Max parallel reconnection trips.

5. Cable check If the input cables to the two Max units are significantly longer or different in length from each other, try to make them as short and symmetrical as possible. Upgrading to thicker cable 10 mm2 on the grid input side could reduce any contribution from impedance, especially if you ever draw more grid current.

If the bypass test or King buffering still shows trips on the main breakers, then the combination of poor earth plus large parallel transient may require a proper on site measurement of leakage current during the switch with a clamp meter that reads mA.This explains the 5 kW vs 8 kW difference quite well it’s the combination of parallel operation, higher power, and the specific relay behaviour of the Max series, made worse by marginal cables and weak earthing.Please keep us posted on the results of the bypass test or the King buffering attempt. If you can also note the approximate cable lengths and sizes to each inverter, that would help refine the advice further.
PowerForum Store

@Powerforum Store Hi i will try this. Did an Axpert VM III 5Kw could do the trick ? I didn't have a King 5K in spare actually for the test 😣

The axpert 5K could share the same battery bank of the max inverters or it must have separate battery ?

If the 5K could use the same battery bank, it could also be used only for charging the batteries from the grid if required. Enabling the grid input of the 5K could be done by an external relay. Also, the output of 5K could go to the max grid input for a complete "bypass mode" . Could you confirm that ?

Best Regards

Edited March 26Mar 26 by fhocorp

Not being an electrician, please wait for feedback from our panel of experts on the following:

Do you have a neutral/earth bonding mechanism in/with your inverter?

Neutral and earth is normally bonded at the electricity provider (grid) side, most often either where power feeds to your house, or at the transformer, and this is the only bonding that should be in place. When "off-grid", you should have a system (either built-in to the inverter, or through a contactor or relay) to make this bond at your inverter (on the load side...) when the grid goes off. If this is omitted, or the wiring not done correctly, you could end up with a voltage on your neutral, and this could perhaps result in the rcb's tripping?

On 2026/03/26 at 7:37 AM, fhocorp said:

I received my 40A Type B residual breakers this week

These are RCCB's(Residual Current Circuit Breakers) they do not have overload protection they are rated for 40A. They will trip if your leakage current exceeds ~ 300mA. You have and earth fault or more that 1 earth fault exceeding 300mA. You need to get a multifunction tester and 1. Check the external earth loop impedance Ze it should be 0.35 ohms for TN-C-S earthing systems and 0.8 ohm for TN-S.

2. Use the multifunctional tester to measure your standing leakage current. By using the scale start with 1/2 and 100ma and work your way up until the RCCB trips. Also ensure you don't have more that 1 earth neutral bond between point of supply and point of consumption or any point beyond point of consumption.

On 2026/03/26 at 7:37 AM, fhocorp said:

Hi

I received my 40A Type B residual breakers this week.

I have installed them, and tried a bypass mode to grid. The new breakers triped.

My 2 axpert max inverters get to much power when going to grid mode ?

Little precision : i am in triphased in my grid installation, but i can't use all the phases due to technical issues so the inverters input is only on one phase. Since i have 12Kva in triphased, i could have only 20A max per phase. How much the axpert max handle at startup at grid mode ?

My old 5Kva axpert King inverters doesn't have to much issue with grid. There is a way to reinstall a 5Kva with it's output dirrectly connected to the axpert max grid input (and of course it's grid input to the grid breakers) ?

I suspect that my grid installation doesn't support the axpert max. Actually, the only way to connect my max to the grid is this way :

• Completely shutdown inverters

• Disconnect PV input and grid input

• Startup the 2 inverters

• Connect the grid input

• Wait for the inverters to connect to grid

• Connect the PV inputs

But even with this method, the breakers trip.

Any ideas @Youda ? 😕

The new breakers pictures are in attachements

Should you have a short curcuit or overload condition your main or sub thermal magnetic breaker will trip without the RCCB's been affected.

One example of a multifunctional tester.(cheapest)

Edited March 27Mar 27 by TaliaB

On 2026/03/16 at 7:47 PM, fhocorp said:

21 hours ago, Powerforum Store said:

If the bypass test or King buffering still shows trips on the main breakers,

Maybe a faulty breaker or like you said, a undersized breaker. But that doesn't explain why the grid main AC breaker of the house that are 120A sized is tripping...

Both conditions in the above statements should never happen. The only time you should trip the overcurrent breaker is in the event of a short circuit or serious overload. Curve C current breakers is rated for 5 to 10 times it rated current. The only instance any inverter could cause large current draw on the ac input when synchronizing to the grid is in the event of the dc bus capacitors not charge up but with battery or pv connected first connecting to grid should be a gentle change over as the inverter is already inverting on synchronization.

In the event of a 120A breaker tripping as described by the op there is a serious problem within the wiring and should be properly investigated and I will strongly advise to shut down the main incoming feed until problem is found as suggest earlier on by @Scorp007

7 hours ago, TaliaB said:

The only instance any inverter could cause large current draw on the ac input when synchronizing to the grid is in the event of the dc bus capacitors not charge up but with battery or pv connected first connecting to grid should be a gentle change over as the inverter is already inverting on synchronization.

I expect this

11 hours ago, TaliaB said:

These are RCCB's(Residual Current Circuit Breakers) they do not have overload protection they are rated for 40A. They will trip if your leakage current exceeds ~ 300mA. You have and earth fault or more that 1 earth fault exceeding 300mA. You need to get a multifunction tester and 1. Check the external earth loop impedance Ze it should be 0.35 ohms for TN-C-S earthing systems and 0.8 ohm for TN-S.

2. Use the multifunctional tester to measure your standing leakage current. By using the scale start with 1/2 and 100ma and work your way up until the RCCB trips. Also ensure you don't have more that 1 earth neutral bond between point of supply and point of consumption or any point beyond point of consumption.

Should you have a short curcuit or overload condition your main or sub thermal magnetic breaker will trip without the RCCB's been affected.

One example of a multifunctional tester.(cheapest)

thanks for you advice. The earth is coming from the mains. No other earth points.

I am expecting the issue found by @Powerforum Store about the parrallel inverters issue whe' they go to grid :

The Axpert Max 8 kW has a higher power rating, larger internal components, and different firmware behaviour. When two units run in parallel, they must synchronise their relays almost perfectly. Even a small mismatch in relay timing a few milliseconds between the master and slave can create a larger neutral-earth current pulse during the changeover. The higher power capability also means any transient imbalance can involve more current, making the leakage spike bigger and more likely to trip sensitive or even 40 A Type B RCDs and upstream breakers.

In this case, i will try to use a King 5K or Axpert VM III 5K for grind feeding. If it works, my grid input will be capped to 5000W max that are sufficient for all my load when i am on grid (i have more loads only in summer when my cooling system is working, and of course in summer i will be in battery mode due to good sunlight so it will be not a problem.).

Best Regards

Hi

Answer after my test.

I have connected a King 5K (found in a local detailer) to my installation and no problems for grid mode to battery mode. I have leaved the grid input of my axpert max disconnected. My King 5K recharge my batteries via grid (a relay connect the grid to the King only when the SOC of the batteries are out of 10%).

I will try to set a custom full bypass mode by connecting the output of my King 5K to the grid input of my 2 Axpert max. I will pry that the breakers does no trip and the King does not fry if mistake happen...(Ineed the in-out of each inverter is protected by breakers).

Best Regards

On 2026/03/26 at 12:42 PM, Powerforum Store said:

Hi Francis @fhocorp ,Thanks for the latest update and for addressing @Scorp007 point directly. You’re correct to highlight the key question: why does the older 5 kW Axpert King handle the grid reconnection without tripping the RCDs, while the parallel pair of 8 kW Axpert Max units cause significant leakage trips even tripping the main 120 A breaker? And whether cable length and size play a role. Why the 5 kW King behaves better than the 8 kW Max in parallel This difference is common and not surprising for these Voltronic models.

• The Axpert King 5 kW is generally a bit gentler on the grid reconnection. Its internal relays, control logic, and neutral earth bonding changeover are tuned differently often with slightly slower or smoother timing. Many users report that the King series has fewer nuisance RCD trips during bypass switching compared to the Max series.

• The Axpert Max 8 kW has a higher power rating, larger internal components, and different firmware behaviour. When two units run in parallel, they must synchronise their relays almost perfectly. Even a small mismatch in relay timing a few milliseconds between the master and slave can create a larger neutral-earth current pulse during the changeover. The higher power capability also means any transient imbalance can involve more current, making the leakage spike bigger and more likely to trip sensitive or even 40 A Type B RCDs and upstream breakers.

• It’s not necessarily that the 8 kW is faulty, but the parallel combination plus higher power amplifies the exact transient that the single 5 kW King can hide more easily. Your poor house earth as you mentioned makes the system even more sensitive to any earth current spike.

Is cable length and size a factor? Yes, it can contribute, but it is usually secondary, not the main cause.

• Longer or undersized cables on the grid input side increase impedance. This can make the voltage sag or the inrush current spike during reconnection slightly worse, which in turn can stress the relays and increase the chance of arcing or imperfect neutral switching means a bigger leakage pulse.

• Your earlier mention of 6 mm2 cable and low grid charging max 20 A per phase on a single phase setup suggests the cables may be marginal when the two 8 kW units try to connect simultaneously. The 5 kW King draws less peak current on reconnection, so the same cables cope better with it.

• However, if the magnetic breakers never trip, the issue is still primarily the short duration residual (leakage) current, not sustained overcurrent. Cable length and size would mainly affect the severity of the transient rather than create it from nothing.

Recommendations considering the latest points given the poor house earth and the clear difference between 5 kW King and 8 kW Max.

1. Do the temporary bypass test on the 40 A Type B RCDs as suggested before. This will quickly tell us whether the pulse is so large that it affects the main breakers even without the input RCDs.

2. Try the King buffering idea you mentioned feed the grid input of the two Max 8 kW units from the output or a spare grid passthrough of one 5 kW King. Let the King connect to the main grid first. Many users find this smooths the transition dramatically because the Max units then see a more stable source.

3. Address the earth quality even if the owners don’t want major repairs, a local electrician could at least improve the earth connection at your distribution board or add a temporary supplementary earth rod for testing. A high earth impedance makes every leakage pulse worse.

4. Consider S type time delayed RCDs on the grid inputs to the Max pair 100 mA or 300 mA S type. This is still the most common successful fix for Max parallel reconnection trips.

5. Cable check If the input cables to the two Max units are significantly longer or different in length from each other, try to make them as short and symmetrical as possible. Upgrading to thicker cable 10 mm2 on the grid input side could reduce any contribution from impedance, especially if you ever draw more grid current.

If the bypass test or King buffering still shows trips on the main breakers, then the combination of poor earth plus large parallel transient may require a proper on site measurement of leakage current during the switch with a clamp meter that reads mA.This explains the 5 kW vs 8 kW difference quite well it’s the combination of parallel operation, higher power, and the specific relay behaviour of the Max series, made worse by marginal cables and weak earthing.Please keep us posted on the results of the bypass test or the King buffering attempt. If you can also note the approximate cable lengths and sizes to each inverter, that would help refine the advice further.
PowerForum Store

Hi @Powerforum Store tried the King 5K output to the grid input of the Axpert max and it works only when the king is in battery mode. When the king is in grid mode, the main breaker strike again, including the type B breakers on the way. I will stop my 2 axpert max for maintenance and searching if them have not a grounding fault inside....

I wonder if it could be a neutral wiring issue somehow.

17 minutes ago, Coulomb said:

I wonder if it could be a neutral wiring issue somehow.

@Coulomb It may be the case, but i couldn't validate this theory without checking the 2 axpert max

Also, one of my axpert max (always the same) sometimes get in fault 09 in the morning. I had to completely disconnect him from battery, grid and PV and completly restarting him. After restart it works normally. The issue appears 2 - 3 times in a month. Maybe a faulty caps or missing neutral screw inside... I will keep you informed about that.

Anyway, i have created a "home made" ATS (based on 2 relays, one for grid input and one for inverters output, with a 3 second timer for avoid grid voltage return to inverters output when switching) with a 5K wired on the grid input for having the telemetry and have the possibility to charge the batteries via the grid if required. If will share the wiring plan of my temporary install here very soon.

Best Regards

On 2026/03/26 at 6:37 AM, fhocorp said:

Hi

I received my 40A Type B residual breakers this week.

I have installed them, and tried a bypass mode to grid. The new breakers triped.

My 2 axpert max inverters get to much power when going to grid mode ?

Little precision : i am in triphased in my grid installation, but i can't use all the phases due to technical issues so the inverters input is only on one phase. Since i have 12Kva in triphased, i could have only 20A max per phase. How much the axpert max handle at startup at grid mode ?

My old 5Kva axpert King inverters doesn't have to much issue with grid. There is a way to reinstall a 5Kva with it's output dirrectly connected to the axpert max grid input (and of course it's grid input to the grid breakers) ?

I suspect that my grid installation doesn't support the axpert max. Actually, the only way to connect my max to the grid is this way :

• Completely shutdown inverters

• Disconnect PV input and grid input

• Startup the 2 inverters

• Connect the grid input

• Wait for the inverters to connect to grid

• Connect the PV inputs

But even with this method, the breakers trip.

Any ideas @Youda ? 😕

The new breakers pictures are in attachements

Yeah, I saw issues just like this in the past - RCD on the input side of inverter tripping when switching between modes. Not on every try, but pretty often.

Just to emphasize, these are RCDs, not MCBs. So it's not a spike or overcurrent, but in most cases the RDCs trip because of imbalance in current passing thru L vs N line. Which is normally caused by leakage current, or by shorting PE+N after the RCD.

Root cause:

• Internal grounding relay (PE+N) of the inverter must be closed in the off-grid mode, but open in the grid mode.

• When inverter is switching between modes and connects AC input to the grid before disconnecting internal PE+N relay, then RCD trips.

• Since it is unsafe to run off-grid mode with the internal relay open, the inverters are trying to minimize the time with PE+N relay open - and sometimes it happens that AC input is already connected while the PE+N relay is not fully opened yet. Then RCD trips.

• For inverters running in parallel it's even worse, as their mode switching logic is much more complicated.

The behavior depends on the logic incorporated in the inverter's firmware. Some models are doing OK, others are causing troubles.

The working solution is to put RCD at the inverter output, not at the input. RCD installed at the inverter input, especially when more inverters are running in parallel, is a free ticket for these troubles.

PS: For example, in my country, RCDs are mandatory for output circuits, like light, sockets, domestic appliances, water pumps, in order to protect users. If these circuits/devices are being fed by the inverters, then there's even more strict requirement - must use Type B RCD, the one that can detect DC currents. But, AFAIK, we have no requirement here to use RCDs for inverter inputs - just MCBs are sufficient.

On 2026/05/16 at 2:22 PM, Youda said:

Yeah, I saw issues just like this in the past - RCD on the input side of inverter tripping when switching between modes. Not on every try, but pretty often.

Just to emphasize, these are RCDs, not MCBs. So it's not a spike or overcurrent, but in most cases the RDCs trip because of imbalance in current passing thru L vs N line. Which is normally caused by leakage current, or by shorting PE+N after the RCD.

Root cause:

• Internal grounding relay (PE+N) of the inverter must be closed in the off-grid mode, but open in the grid mode.

• When inverter is switching between modes and connects AC input to the grid before disconnecting internal PE+N relay, then RCD trips.

• Since it is unsafe to run off-grid mode with the internal relay open, the inverters are trying to minimize the time with PE+N relay open - and sometimes it happens that AC input is already connected while the PE+N relay is not fully opened yet. Then RCD trips.

• For inverters running in parallel it's even worse, as their mode switching logic is much more complicated.

The behavior depends on the logic incorporated in the inverter's firmware. Some models are doing OK, others are causing troubles.

The working solution is to put RCD at the inverter output, not at the input. RCD installed at the inverter input, especially when more inverters are running in parallel, is a free ticket for these troubles.

PS: For example, in my country, RCDs are mandatory for output circuits, like light, sockets, domestic appliances, water pumps, in order to protect users. If these circuits/devices are being fed by the inverters, then there's even more strict requirement - must use Type B RCD, the one that can detect DC currents. But, AFAIK, we have no requirement here to use RCDs for inverter inputs - just MCBs are sufficient.

Hi. Thanks for your answer. Actually, i have placed a Axpert King 5000W for grid input. I have installed a "custom" ATS system for switching to grid or to battery input.

The system is composed of 2 relay :

• one for AC GRID input

• one for the AC Output of the 2 Axpert 8000W i use for solar and battery mode that works

  The relays are controlled by each AC input comming to the breakers. When the system is on battery, the output relay is ON, and the Grid Relay is OFF, so the house appliances are feed by the 2 Axpert 8000W (max 16Kw output because they are in parrallel).

  When the batteries are low, the 2 Axpert 8000W inverters will shut down. The AC ouput of the inverters is shutdown so the Inverter AC output relay in my system gos the the OFF position. The grid output relay is activated and AC output is feed by the grid (the Axpert King 5000W is wired in bypass mode for grid input to direct output, the usage of axpert King 5000W here is just for having the metrics of the grid usage only and since the Axpert King also have solar panels connected to him it reduces my grid usage).

I have add a timer for switching from grid to inverter output (3 seconds timer, during this time the house is completely with no AC, for allowing the relay to completely moving without spikes) since i am not very confident in my system and i don't want to risk a reverse current flow from the grid back to the inverters and burn them out.

Yes, this is a clumsy system but it is the only solution i have found actually for automating this system. The wiring of my house allow only 20A max for grid and we have to rewire completely the house but the owners don't want to make this at this time 😔

Edited May 18May 18 by fhocorp