Jump to content

Axpert Floating neutral


Edison
 Share

Recommended Posts

Buy a proper inverter that does it right...

OK, I'm kidding, well, half kidding. This question comes up twice a week 🙂

First Axperts (circa 2013) had no proper bonding in place.

Later versions had a firmware setting (38 I believe from a quick google) that could be enabled. This would then use the internal relay in the inverter to switch an external bonding relay that would tie T and N together when running islanded.

Later versions of the Axpert (2017 ish?) had a proper fix and bonds TN using the same relay that switches the neutral side of the grid connection.

I doubt there can be very many of the 2013 vintage Axperts still around, since they generally don't last that long, so you will probably have the firmware setting as mentioned.

If not, revert to the first sentence of this post 🙂

 

Link to comment
Share on other sites

6 hours ago, plonkster said:

Later versions of the Axpert (2017 ish?) had a proper fix and bonds TN using the same relay that switches the neutral side of the grid connection.

I'm only aware of the models that came with firmware version 73.00 that have this automatic neutral to earth relay connection. I just had a look at the latest Axpert MKS II firmware (version 71.82), and it doesn't even have setting 38 to enable an external relay. Somehow, they seem to have forgotten the need for this in some models.

At least the latest firmware version 74.40 for Axpert MKS PF1.0 with 58.4 V max have setting 38; I don't know if they have the relay connection or not. My guess is that the lack of setting 38 implies the lack of automatic relay connection.

Axpert MKS PF1.0 64 V max (firmware version 72.20) also has setting 38, I also don't know if they have the relay connection or not.

Axpert King firmware version 71.92 does not have setting 38.

It's easy to tell with a multimeter before installing; models with the automatic relay connection of AC-out neutral to earth will have AC-out neutral connected to earth when not powered up. When AC-in is connected to AC-out, the connection will be automatically removed (relying on the neutral-to-earth connection at the switchboard, which should always be there).

TLDR: Not all new models have the automatic neutral connection feature.

 

Link to comment
Share on other sites

1 hour ago, Coulomb said:

TLDR: Not all new models have the automatic neutral connection feature.

Right. So I suppose it is important to explain that this TN bonding isn't handled the same in every country, and as @Coulomb pointed out in the past, it is certainly less of an issue in Australia and NZ.

Even in South Africa, if you have a TN-C-S connection to your supplier, ie the main breaker in your kiosk (meterkast in Dutch) is single pole, and you install the inverter at this point, then you can simply connect the input neutral and output neutral together and be done. But the majority of South African installations are not like this.

So the options are:

1. Simply bond TN together on the output. This violates SANS (which requires that earth conductors should only carry fault current).

2. Connect the input and output neutrals together. This violates SANS (which requires that you don't rely on the council-side TN bond for islanded operation).

3. Install a contactor with normally-closed contacts that's powered by the grid, and use a NC contact to bond TN. When the grid fails, the contactor installs the bond. This is no good for systems with solar power, since those systems may change to islanded operation while the grid remains on.

4. Do nothing. Without the TN bond a singe earth fault may not be enough to trip an RCD (aka earth leakage), but in such a case a single earth fault also doesn't electrocute anyone. Only the second fault trips/electrocutes.

5. Open the inverter and modify it internally so that you can get a signal from the changeover relay, and use that to make your own bonding box. Voids warranty.

6. Replace the inverter with one that complies.

The first 4 are not compliant of course.

Link to comment
Share on other sites

  • 1 month later...

My Axpert(Synerji) MKS 5k with firmware 74 40 came with the N of the inverter internally connected to earth. This bothered me because I wired the N of inverter and of charger together in order to save 25m of N wire. It tripped the earth leakage protection in the DP. As the seller would not help me I opened the inverter. I found underneath the microprocessor board on the inverter board a screw labeled with the earth symbol and a symbol indicating that it can be removed. I removed it and the N to earth connection was gone.

I wired my system in that way that N remains always connected to grid N even when operating off grid with solar panels or battery. I now worked out a DP scheme with the inverter input connected to the earth leakage protection. As off grid operation shall be the normal operation mode I will always have this protection, even if the inverter switches to utility bypass mode.

Link to comment
Share on other sites

Relay, base for relay.

Wire it so that the normally closed is connected to ground, common is connected to inverter neutral.  Normally open is not connected to anything.  Coil is connected to utility power (NOT inverter output).

On 2020/08/18 at 8:24 AM, ___ said:

4. Do nothing. Without the TN bond a singe earth fault may not be enough to trip an RCD (aka earth leakage), but in such a case a single earth fault also doesn't electrocute anyone. Only the second fault trips/electrocutes.

It guaranteed will cause an earth leakage to stop working.  I can say this with 100% confidence because I've tested it on an Axpert inverter.  Even significant leakage has absolutely no effect.  It is hardly unique to Axpert inverters but I tested it for sh!ts and giggles anyway.  It will also result in any electronics that relay on ground for noise rejection to float at mains voltage.  For example, my Macbook charger connects the outer USB outer metal part to earth.  Without it connected to earth it is floating at line voltage, the amount of energy in joules is insignificantly but if you touch the charger and an actual ground at the same time, you can feel it sting.  This isn't unique to Macbook chargers, a lot of AC->DC adapters use decoupling capacitors for ripple rejection.

Similarly a lot of electronics with metal body relay on the protective earth and the earth wire is directly connected to body of the metal.  Plugs and light switches with metal bodies have earth connected to the metal parts.

Point being, you are massively understating the danger in a floating earth.  There are two significant risks, the first is that your earth wire is floating at some potential, in which case the risk of electrocution exists regardless of a fault.  The second risk is that any fault in the circuit will pull all the earth connections to that potential, that is crazy dangerous.

Edited by Gnome
Link to comment
Share on other sites

On 2020/08/18 at 7:08 AM, Coulomb said:

Axpert King firmware version 71.92 does not have setting 38.

I never saw that setting but regardless the neutral and ground are connected (tested this for obvious reasons).  I suspect they are doing this with a relay.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...