Axpert invertors

[Marvo]

And what do you think am I?

1) The regulations about this is very clear IMHO,
2) If you know how electricity work (especially from the transmission / distribution side of things), you'd have clear understanding of why this is required,
2.1) When you're Inverter is in "bypass" mode, the load is connected to your existing Neutral/Earth bond, regardless of where it has been made, be it in your DB, main junction, street cabinet, hell even at your sub station...
2.2) When you're inverter is in battery mode, it is NO LONGER CONNECTED to the Neutral/Earth bond that pre-existed (be it in your DB, main junction, street cabinet, hell even in your sub station...)
3) Seeing that your load can be disconnected from the distribution/transmission, and in doing so loose it's earth/neutral bond, a new one MUST be created.

Without going in too much detail, all this grounding ensures that the AC wiring is kept near earth potential, and won't drift up to 12 KV due to a fault in the distribution transformer.

A (american unfortunately) video explaining all of this in a bit more detail available at https://www.youtube.com/watch?v=-n8CiU_6KqE (a simpler version at https://www.youtube.com/watch?v=0MQR-tT7DLg. We DO bond in the sub panels (after the inverter), because the Inverter BREAKS the Neutral connection (which is already bonded) when it operates in battery mode. When looking at the video, please keep in mind this is to explain the THEORY behind WHY it is being done, not HOW to do it (take note of the discussions regarding broken connections - this is what your inverter does in battery mode - it DISCONNECTS from the supply)...

https://www.youtube.com/watch?v=ZL8zrkahuL0 A simple summary. And lastly, a very nice animation explaining the history behind it, and WHY it is being done https://www.youtube.com/watch?v=k3OHzKz0qNc (short and sweet)... This last one, actually summarizes it very nicely.

I hope that this now clears it up...

EDIT: And on a side note, I never have, and never WILL encourage, nor endorse an unqualified person messing about in any electrical installation either.

I have a vague idea about electricity but every day is a school day.

If you bond the neutral and the earth on the output side of the inverter, unless the inverter provides electrical isolation between its input and output then when it's in bypass mode (Eskom supply is present) you will have created an unwanted neutral - earth connection.

Yes, when the inverter goes into battery power mode then that N-E connection is necessary to tie the neutral to zero volts and prevent it 'floating' but as soon as the power is restored then that extra N-E bond becomes surplus because the N+E are already bonded on the council side before the point of supply.

IMHO installing a permanent N-E bond that's present when power is restored would be a departure from the connection scheme shown in Amdt 8 Diagram S3 page 357.

Also SANS10142 6.1.6 The neutral conductor shall not be connected direct to earth or to
the earth continuity conductor on the load side of the point of control.

 

[savage]

Also SANS10142 6.1.6 The neutral conductor shall not be connected direct to earth or to
the earth continuity conductor on the load side of the point of control.

For a "standard" installation with one point of supply, yes, absolutely. Just on this, the definitions say:

3.56
point of control
point at which a consumer can, on or in any premises, switch off the
electrical installation from the electricity supplied from the point of supply

3.58
point of supply
point at which a supplier supplies electricity to any premises

When your inverter operates in battery mode (be it your inverter, UPS, or generator), you BECOME the point of supply.

As the bond is made after the Inverter's output (load side of the genset), but before the breakers that isolate the load (dbl pole breaker on the load side of the inverter, before distributing off to your various circuit breakers), your are not yet on the load side of the point of control in terms of the installation - you are just on the load side of your generator, or the point of supply. This is why I always preach dbl pole breaker on your main supply AND load to/from your inverter to your DB.

I know this is complicated, but you need to think from the point of view that you are becoming your own little Eskom, in that you generate and supply your own power. You become the point of supply.

Yes, when the inverter is in bypass mode, technically, the inverter will be part of the point of control - I don't argue this at all. Alternative points of supplies (i.e. generators, UPSes, Inverters, etc.) are for this very reason, treated differently according to SANS10142, and hence are special circumstances dealing with this specifically. That is why you will see that throughout SANS10142, various exceptions and various other requirements that are stipulated SPECIFICALLY for when dealing with generators (alternative points of supply). Frankly, you have an entire section (7.12) dealing with Alternative Supplies for this very specific reason.

We can really argue about this until kingdom come if you want. This is how I install them and over the years I more than likely installed more than 200 UPS/Generator systems, and I think close to about 30 inverters...

Yes, when the inverter goes into battery power mode then that N-E connection is necessary to tie the neutral to zero volts and prevent it 'floating' but as soon as the power is restored then that extra N-E bond is no longer functional because the N+E are already bonded on the council side before the point of supply.

Then install a N/C relay on the bond, so that the relay is only open when the inverter has supply voltage (neutral is connected), and closed when the supply is disconnected (when the inverter's supply is off) if that makes you feel better. Hopefully you won't get any feedback surges, but then again whether there's feedback surges or stray voltages, it's just as dangerous to you, and your equipment.

If you do feel that strongly about it (and I don't agree with this), then you would need to ISOLATE the earths as well (before & after the inverter), in that the earth before the inverter, and the earth behind the inverter (which is now bonded to two "separate" neutrals) do not form a continuous circuit. That means a dedicated earth spike, far enough from your existing earth spike, so that current cannot flow between the two earth spikes through the ground. So whether the inverter is in bypass mode, or battery mode, the earths are not connected at all, and therefore no "unwanted" earth/neutral connection.

This BTW, is called an Isolated Earth. It's mostly how Hospitals are wired (amongst other things), and the requirements there become SO strict (there are numerous changes / differences), that no one EXCEPT a Master Installation Electrician may work on the installations...

Just for the record, but I've had about a 3 hour long discussion about this exact same thing with a Master Installation Electrician, with close to 30 years experience In Diagram S3 on page 357, they have ASSUMED that the UPS has an internal Neutral/Earth bond (And this means Incoming Neutral, Incoming Earth, Outgoing Neutral, Outgoing Earth - all four - is bonded together). We KNOW that the Axpert does NOT have an internal Earth/Neutral bond. That's the difference here. It's the same with generators. Some HAVE internal Earth/Neutral bonds, and some DON'T.

As an electrical contractor / installer, you need to KNOW what you are installing, and HOW to install it. That's really the bottom line here. Testing whether equipment is internally bonded or not, or testing whether a generator / inverter has a V-O-V Ground (which makes it illegal to connect to a fixed electrical installation), is really a 2 second job and child's play for anyone that is actually worth it to have a basic wireman's license in any case.

I don't think this get's much clearer however...

7.12.3.1.3 Where alternative supplies are installed remotely from the installation, or from one another, and where it is not possible to make use of a single neutral bar which is earthed, the neutral of each unit shall be earthed at the unit and these points shall be bonded to the consumer's earth terminal (see 6.12.4). The supply from each unit which supplies the installation or part of the installation, shall be switched by means of a switch that breaks all live conductors operating substantially together (see annex S), to disconnect the earthed neutral point from the installation neutral when the alternative supply is not connected (see also 6.1.6).

I think you need to watch this - it's long, but -very- informative. It really explains a lot of the how's, but more importantly, the WHYs...
[video=youtube;mpgAVE4UwFw]https://www.youtube.com/watch?v=mpgAVE4UwFw[/video]

Yes, it's american and based on american standards, but the theory stays the same. electricity, is electricity, is electricity.

 

[DollyAAAA]

Then there's no need to bond THAT neutral again - just measure it to be sure. A simple volt reading between neutral & earth, if you don't get 0V, then it's not bonded, in which case you can proceed to bond it. Only bond the neutral from the Inverter's load side, if your supply is already bonded (i.e. don't bond twice, especially not in two separate locations - it will make fault finding / troubleshooting very difficult). You need to do the bonding before any earth leakages. If your inverter's supply is after a earth leakage, you can't bond either (e/l will trip in bypass mode), hence why I'm always preaching that the inverter's supply should NOT be behind a E/L device.

Yeah, I was referring to my inverter's output neutral bonding. Already verified that my Eskom supply IS bonded and that my Axpert wasn't bonded internally (see previous posts - I've measured the floating neutral in battery mode). You have also confirmed this. So the ONLY bonding that I have done is right on the output of the inverter, as per your recommendation.

 

[ray-zin]

We have a 5KVA, with 3000W panels and 240Ah battery bank and I run the whole house, excluding stove off it.

I see that you are in the JHB area. Did you have a contractor install your axpert etc? - If so... would you mind sharing who? (Also... would you recommend them?)

thanks. R.

 

[savage]

You have also confirmed this. So the ONLY bonding that I have done is right on the output of the inverter, as per your recommendation.

hehe, ok Can't remember everything about everyone You should be fine then.

 

[knoop]

I can't say when (it's too early days), but I will be getting rid of my Axpert 5KVA at some point (want an Infini rather - better with the PV), and I'll more than likely add another 100Ah or 200Ah to my system as well at that stage.

What advantage does the Infini have over the Axpert? Can it be bought online locally?

 

[savage]

What advantage does the Infini have over the Axpert? Can it be bought online locally?

The Infini syncs with the grid (but does not feed back if configured not to do so)... This has advantages.

Axpert:
If you have a 1kW load running, but you are only able to get 800W from PV (i.e. you're 200W short), the entire 1kW load is switched into bypass mode (i.e. pulled from Eskom), or it adds the missing power from battery - potentially draining your batteries just before load shedding is scheduled to start. i.e., it pulls from only one supply in order to facilitate the load.

Infini:
If you have a 1kW load running, but you are only able to get 800W from PV (i.e. you're 200W short), the remaining 200W is pulled from Eskom. i.e., it pulls from all supplies simultaneously in order to facilitate the load.

If you use a lot of power during the day (i.e. work from home / stay at home moms / etc), then it becomes more viable for something like the infini, as it doesn't 'switch off' your PV when the load becomes too great - it supplements it.

 

[knoop]

Gotcha, that sounds like what I need. Thank you.

 

[DollyAAAA]

The Infini syncs with the grid (but does not feed back if configured not to do so)... This has advantages.

Axpert:
If you have a 1kW load running, but you are only able to get 800W from PV (i.e. you're 200W short), the entire 1kW load is switched into bypass mode (i.e. pulled from Eskom), or it adds the missing power from battery - potentially draining your batteries just before load shedding is scheduled to start. i.e., it pulls from only one supply in order to facilitate the load.

Infini:
If you have a 1kW load running, but you are only able to get 800W from PV (i.e. you're 200W short), the remaining 200W is pulled from Eskom. i.e., it pulls from all supplies simultaneously in order to facilitate the load.

If you use a lot of power during the day (i.e. work from home / stay at home moms / etc), then it becomes more viable for something like the infini, as it doesn't 'switch off' your PV when the load becomes too great - it supplements it.

Very well explained.

You get what you pay for, though. More functionality/quality, more dosh. My Axpert does what I want from it right now (bridge the load shedding gap), but the Infini is a far better solution if you're trying to become more independent from Eskom or save on your Eskom bill.

Savage, quick question: If you run 2.5mm[SUP]2[/SUP] house wire through a 20mm conduit (typical plug circuit), are you limited to a 20A breaker if the cable run is only say 10m? Can you up the breaker for shorter cable runs? I believe somewhere in the SANS standard there is a table for this sort of calculation.

 

[Marvo]

For a "standard" installation with one point of supply, yes, absolutely. Just on this, the definitions say:

3.56
point of control
point at which a consumer can, on or in any premises, switch off the
electrical installation from the electricity supplied from the point of supply

3.58
point of supply
point at which a supplier supplies electricity to any premises

When your inverter operates in battery mode (be it your inverter, UPS, or generator), you BECOME the point of supply.

As the bond is made after the Inverter's output (load side of the genset), but before the breakers that isolate the load (dbl pole breaker on the load side of the inverter, before distributing off to your various circuit breakers), your are not yet on the load side of the point of control in terms of the installation - you are just on the load side of your generator, or the point of supply. This is why I always preach dbl pole breaker on your main supply AND load to/from your inverter to your DB.

I know this is complicated, but you need to think from the point of view that you are becoming your own little Eskom, in that you generate and supply your own power. You become the point of supply.

My issue with the E-N bond isn't when the inverter is the point of supply, What you say above is correct.

My concern is about that N-E bond remaining after Eskom supply is restored. This is the time it would be in breach of the regs and this is when it could possibly introduce a hazardous condition within the boundaries of the customer installation.

Yes, when the inverter is in bypass mode, technically, the inverter will be part of the point of control - I don't argue this at all. Alternative points of supplies (i.e. generators, UPSes, Inverters, etc.) are for this very reason, treated differently according to SANS10142, and hence are special circumstances dealing with this specifically. That is why you will see that throughout SANS10142, various exceptions and various other requirements that are stipulated SPECIFICALLY for when dealing with generators (alternative points of supply). Frankly, you have an entire section (7.12) dealing with Alternative Supplies for this very specific reason.

Special attention has been given in the 10142 regs to installations with alternative supplies because back-up generators and UPS's/inverters are notorious for introducing hazards that are unlikely to occur on a standard installation. The persistent N-E bond that we're discussing within the installation is one of these hazards.

We can really argue about this until kingdom come if you want. This is how I install them and over the years I more than likely installed more than 200 UPS/Generator systems, and I think close to about 30 inverters...

I think this method of installation is contentious, and there are relevant regulations that back this up so it's definitely a valid debate. I'm not looking for an argument, I'm just expressing concerns.

Then install a N/C relay on the bond, so that the relay is only open when the inverter has supply voltage (neutral is connected), and closed when the supply is disconnected (when the inverter's supply is off) if that makes you feel better. Hopefully you won't get any feedback surges, but then again whether there's feedback surges or stray voltages, it's just as dangerous to you, and your equipment.

This isn't about making me feel better but this is the direction I'm thinking but firstly lets get surges and transients out of the way. Bonding the N+E within an electrical installation (after the point of control) isn't and never has been a recognized method of preventing surge damage on a residential installation.

The direction this debate is taking me is that this issue is identical to the issues with cheap camping/site type generators with no N-E bond being used for residential back-up supplies. Neither these generators nor the Axpert inverters are inherrently designed to be connected this way.

If you do feel that strongly about it (and I don't agree with this), then you would need to ISOLATE the earths as well (before & after the inverter), in that the earth before the inverter, and the earth behind the inverter (which is now bonded to two "separate" neutrals) do not form a continuous circuit. That means a dedicated earth spike, far enough from your existing earth spike, so that current cannot flow between the two earth spikes through the ground. So whether the inverter is in bypass mode, or battery mode, the earths are not connected at all, and therefore no "unwanted" earth/neutral connection.

It would be preferable if the internal switching of the inverter included switching of the E-N bond when it changed modes of operation. I'm not an expert on these particular inverters but it doesn't sound like this is the case. This bond being persistant after Eskom power is restored is not legal within the existing regs. Yes you could install the Axpert as a TT earthed arrangement with a rod outside the sphere of influence of the existing T N CS (PME) installation but it wouldn't achieve anything without isolating the bond during bypass mode.

This BTW, is called an Isolated Earth. It's mostly how Hospitals are wired (amongst other things), and the requirements there become SO strict (there are numerous changes / differences), that no one EXCEPT a Master Installation Electrician may work on the installations...

I'm confused by this, you're referring to an IT earthing arrangement?

Just for the record, but I've had about a 3 hour long discussion about this exact same thing with a Master Installation Electrician, with close to 30 years experience In Diagram S3 on page 357, they have ASSUMED that the UPS has an internal Neutral/Earth bond (And this means Incoming Neutral, Incoming Earth, Outgoing Neutral, Outgoing Earth - all four - is bonded together). We KNOW that the Axpert does NOT have an internal Earth/Neutral bond. That's the difference here. It's the same with generators. Some HAVE internal Earth/Neutral bonds, and some DON'T.

I'm not sure what to say to this. Assuming something is a dangerous way to approach it and assuming that something has been assumed is really dangerous to the power of two. If the regulations intended the assumption of an internal N-E bond within the inverter they would have shown it as a dotted line inside the inverter that's depicted in the drawing.

As an electrical contractor / installer, you need to KNOW what you are installing, and HOW to install it. That's really the bottom line here. Testing whether equipment is internally bonded or not, or testing whether a generator / inverter has a V-O-V Ground (which makes it illegal to connect to a fixed electrical installation), is really a 2 second job and child's play for anyone that is actually worth it to have a basic wireman's license in any case.

This is really the ground zero of where my questions are coming from. Is the Axpert not just another piece of equipment that's not suitable for installation as an integrated domestic back-up solution because the lack of a switched internal N-E bond means it can't meet the installation requirements in the regs?

 

[ray-zin]

Infini:
If you have a 1kW load running, but you are only able to get 800W from PV (i.e. you're 200W short), the remaining 200W is pulled from Eskom. i.e., it pulls from all supplies simultaneously in order to facilitate the load.

If you use a lot of power during the day (i.e. work from home / stay at home moms / etc), then it becomes more viable for something like the infini, as it doesn't 'switch off' your PV when the load becomes too great - it supplements it.

Hmmmm. i'm liking the sound of that. - Seems like the infini's are pricey.... but not all that much more than the axperts. (as they are priced now).

 

[savage]

Hmmmm. i'm liking the sound of that. - Seems like the infini's are pricey.... but not all that much more than the axperts. (as they are priced now).

Indeed. And as Dolly stated, it boils down to what your long term goals are. Generally when PV is involved, I advise customers against an Axpert, and rather opt for the Infini (or something else, bigger / better - they do exist). If your intentions are purely to get past Load Shedding - sure, there is nothing wrong with the Axpert. If however (as Dolly put it so nicely), you plan to reduce your your dependence on Eskom from a usage/billing point of view, the capabilities and functionality of the Inverter plays a much bigger role, and much more attention needs to be given to it.

Savage, quick question: If you run 2.5mm[SUP]2[/SUP] house wire through a 20mm conduit (typical plug circuit), are you limited to a 20A breaker if the cable run is only say 10m? Can you up the breaker for shorter cable runs? I believe somewhere in the SANS standard there is a table for this sort of calculation.

You are correct in that there are calculations to work this out, and potentially yes, you could possibly get away with a bit of a bigger breaker (although, from 20A, your next step is a 32A breaker, which is MUCH bigger). It's again one of those things however that will more than likely be frowned upon by industry however.

In cases such as this, it's really better in the long term to just stick to what is industry standard. At a cost of R50/R80 for a breaker, it will just save you the hours and hours of hassles in arguing over something that really is at the end of the day, trivial.

1.5mm cable - 10A Breaker
2.5mm cable - 20A Breaker

 

[DollyAAAA]

You are correct in that there is calculations to work this out, and potentially yes, you could possibly get away with a bit of a bigger breaker (although, from 20A, your next step is a 32A breaker, which is MUCH bigger). It's again one of those things however that will more than likely be frowned upon by industry however.

In cases such as this, it's really better in the long term to just stick to what is industry standard. At a cost of R50/R80 for a breaker, it will just save you the hours and hours of hassles in arguing over something that really is at the end of the day, trivial.

1.5mm cable - 10A Breaker
2.5mm cable - 20A Breaker

Cool, thanks. What is the next size up in terms of wire? 4mm with 40A breaker?

I'm really dreading replacing the wire...

 

[savage]

Cool, thanks. What is the next size up in terms of wire? 4mm with 40A breaker?

I'm really dreading replacing the wire...

1.5mm or smaller - 10A or smaller (1A, 2A, 6A, and a few others are options in terms of breakers - but $$$$)
2.5mm or 4.0mm - 20A or smaller
6.0mm or 10mm - 32A or smaller
16.0mm - 40A or smaller

63A is however used and "standard" for 10mm or 16mm cable - especially on the supply side, but this is due to the type of cable used, and how the cable is laid (buried). Over and above 10mm (16mm max), shouldn't be in any "average" residential installation, so I'm not going to bother going on with bigger cables... It does go up to like 500A on 300mm cable, or even 3kA on 4x630mm cable though

Remember, the fundamentals of a breaker is NOT to protect the equipment (that's what earth is for - equipment/system grounding), it's to protect the CABLE from burning / melting...

If you're dreading this in terms of pulling through conduit...
- A fish line / pulling line is a MUST, and get a good quality one.
- Lubricant in the pipe (even Q20) helps ENORMOUSLY!
- If you have one person aiding in feeding the cables and one person pulling on the otherside, with a bit (ok a lot) of lube - it goes very easily... You may just be surprised.

 

[DollyAAAA]

It does go up to like 500A on 300mm cable, or even 3kA on 4x630mm cable though

At the factory where I work we have the city supply us with 120mm[SUP]2[/SUP] and 185mm[SUP]2[/SUP] aluminium cable for a 500A 3 phase supply.

Remember, the fundamentals of a breaker is NOT to protect the equipment (that's what earth is for - equipment/system grounding), it's to protect the CABLE from burning / melting...

^THIS^ is key. The breaker should be the weakest point, not the wire.

If you're dreading this in terms of pulling through conduit...
- A fish line / pulling line is a MUST, and get a good quality one.
- Lubricant in the pipe (even Q20) helps ENORMOUSLY!
- If you have one person aiding in feeding the cables and one person pulling on the otherside, with a bit (ok a lot) of lube - it goes very easily... You may just be surprised.

The cable pulling itself isn't so bad. It's taking out the DB guts to get my hands to where the conduit comes in. Then putting the damn thing back into the wall...

EDIT: "There's always time for lubricant" - cracks me up every time
[video]https://youtu.be/4wvbnR_cT0A[/video]

 

[Dimpie (JIGSAW)]

 

[ray-zin]

Indeed. And as Dolly stated, it boils down to what your long term goals are. Generally when PV is involved, I advise customers against an Axpert, and rather opt for the Infini (or something else, bigger / better - they do exist). If your intentions are purely to get past Load Shedding - sure, there is nothing wrong with the Axpert. If however (as Dolly put it so nicely), you plan to reduce your your dependence on Eskom from a usage/billing point of view, the capabilities and functionality of the Inverter plays a much bigger role, and much more attention needs to be given to it.

This is definitely my aim in future.

I was just looking at the InfiniSolar 3KW to see if it would suit my current needs.

My prepaid meter says I used 60kwh in the last 24 hours which (according to online calculators) equates to around 2700w per hour needed.

So am I correct in thinking that the 3000w of the InfiniSolar 3KW would mostly suit my requirements. (I'm aware that the 2700w would not be the peak hour and is only an average)

I do plan to reduce my usage in future (gas geyser and stove) and will have a very light load when running on battery only during load shedding.

 

[savage]

My prepaid meter says I used 60kwh in the last 24 hours which (according to online calculators) equates to around 2700w per hour needed.

So am I correct in thinking that the 3000w of the InfiniSolar 3KW would mostly suit my requirements. (I'm aware that the 2700w would not be the peak hour and is only an average)

That would be a bit of a big assumption IMHO. You more than likely require quite a bit less than that (which is not a big problem inverter wise, but could be a issue PV / battery wise). Those readings will include things like boiling a kettle, geyser, stove, etc.

Best thing would be to measure accurately what everything uses that you want to power from the Inverter, and plan the correct sized batteries and PV from there.

 

[ray-zin]

... Those readings will include things like boiling a kettle, geyser, stove, etc.

Best thing would be to measure accurately what everything uses that you want to power from the Inverter, and plan the correct sized batteries and PV from there.

Perfect. Thanks for your response.

I think we're on the same page. I was looking at my max (more or less) need inverter wise.

Now that I know what size inverter I'm looking at I can start planning budget wise.

PV's I'll worry about later. Battery window shopping (for load shedding) and calculations are next in my journey to solar enlightenment. (wallet lightenment too!)

Time to get out the old effergy and do some load shedding load investigations.

All the reading of these forums the last few months is definitely helping me understand better all the different components and complexities around this subject.

Thanks again.

 

[blacknight72]

Hi Savage, I am getting another contractor today to help me with the installation. Since you are using the same batteries as me (Trojan T125) can you please mention the settings you used in your Axpert for these batteries. Are there any settings relating to temperature for batteries? Most technicians are feeling that there is something wrong with the settings. There are few installers with any experience with Axpert in my town and the support from Mustek ( distributor) itself is rather disappointing.