Axpert earthing query

[Wisey]

Hi Everyone

And thanks to the administrator for accepting my profile on this site.

I have the following equipment to be installed:

4 x 48V 5KVA Axpert inverters

24 x 250Ah 12V Sonic batteries (6 strings of 48V) 

42 x 250 Watt PV panels

1 x 20KVA Diesel generator 

Only yesterday, through this site (and not the supplier) I learned the Axpert inverter cannot be certified compliant unless it is classified as a 'UPS'. Please see attached wiring diagram sent by the supplier.

For me this is catastrophic from a safety POV and obviously the lack of connection capability to the municipal Earth to qualify for the COC.

My questions please:

1) Does anyone know of a way around the common earthing issue and a method of tying into the municipal earth?

2) I understand the thermal magnetic trip switch on the earth leakage relay (Chint 63A) is obviously not connected to municipal earth. So is there any reason it is insufficient as a protection mechanism in the event of the specified 30Ma rating and thermal increase in the conductor. Can it be relied upon (obviously after being tested) to provide adequate earth leakage protection from the Axpert inverter ?  

Thanks in anticipation of your responses

All the best

Wisey  

 

 

 

 

[Jaco De Jongh]

Firstly, Welcome Wisey

36 minutes ago, Wisey said:

1) Does anyone know of a way around the common earthing issue and a method of tying into the municipal earth?

I am not sure I understand this question, but earthing should be done as this picture shows. With the wires from the main DB/Supply to the inverter you can run an earth wire not less than halve the size of the main current carrying constructor and connect that to the earth terminal. From that terminal i normal bridge the earth wire to the casing of the inverter. You shouls see the screw with an earth indicator next to it, normally on the bottom of the casing. 

42 minutes ago, Wisey said:

2) I understand the thermal magnetic trip switch on the earth leakage relay (Chint 63A) is obviously not connected to municipal earth. So is there any reason it is insufficient as a protection mechanism in the event of the specified 30Ma rating and thermal increase in the conductor. Can it be relied upon (obviously after being tested) to provide adequate earth leakage protection from the Axpert inverter ? 

Chint should be sufficient. The best way is to test it. If it doesn't trip it should be fine. If the RCD cant work with the inverter is will fairly quickly heat up or simply trip. Just remember. you will need one on the input side as well as the output side of the Inverter. 

[___]

There seems to be many issues muddled up together.

Yes, there are questions about the legality of connecting the Axpert's input to the grid, because it is unclear if the internal transfer switch inside the unit is SANS compliant. Technically this makes it illegal for grid connection even as a UPS.

You can however use another changeover switch on the output, and I found out yesterday that apparently this is what some installers now do (they use a simple ABB changeover contactor, which is technically not completely quite right either, but it is mechanically interlocking and has proper clearance gaps).

But the question relating to this legality is separate from the question of earthing, which I believe is rather the question about bonding earth and neutral while running from the inverter. The newer models can use the dry contact relay to switch another relay/contactor that establishes the bond when it disconnects the grid. If you have such a model, then it's a matter of buying some hardware and wiring it up.

If the bond is in place, then a downstream RCD will work correctly, as it operates only on the difference in current in the conductors.

I think this might be a good time to note that an RCD will work EVEN without the N-PE bond, it just takes significantly higher fault currents and/or multiple earth faults before it does. The reason you make the bond is to ensure that a single fault is sufficient to trip the RCD. Without the bond a single fault might go undetected until a second fault shows up.

[Gnome]

9 hours ago, Jaco de Jongh said:

Chint should be sufficient. The best way is to test it. If it doesn't trip it should be fine. If the RCD cant work with the inverter is will fairly quickly heat up or simply trip. Just remember. you will need one on the input side as well as the output side of the Inverter. 

Such an RCD doesn't exist. Unless you mean "modified sine wave" which should really read stepped square wave approximating a sine wave. Any RCD will work with an "Axpert", the sine wave output is completely indistinguishable from Eskom power.

The RCD needs to work on-grid and off-grid. The off-grid is something you especially need to test. By that I mean disconnected the input live and neutral and check that the RCD still trips when you produce an earth leakage. Simplest way to do that is to connect the earth to neutral after the RCD and see that it trips.

If it doesn't trip the earth and neutral need to be bonded at inverter output terminal. But if your inverter itself is connected via an RCD branch that will cause the breaker to open, so obviously that means the earth neutral bond needs to happen on a circuit not protected by an RCD

The test button alone is likely not sufficient testing.

I also can't help but notice you say nothing about circuit breakers. I assume you know that an RCD doesn't provide over current protection. The 63a rating simply means it can handle up to 63a before exploding on you

Edited October 24, 2018 by Gnome

[Jaco De Jongh]

1 hour ago, Gnome said:

Such an RCD doesn't exist. Unless you mean "modified sine wave" which should really read stepped square wave approximating a sine wave. Any RCD will work with an "Axpert", the sine wave output is completely indistinguishable from Eskom power.

That is what I thought as well .. please read This.

And this is not the first time I experience something like this. 

 

[___]

1 hour ago, Gnome said:

The test button alone is likely not sufficient testing.

RCD testers are like R250 :-)

[Jaco De Jongh]

1 hour ago, Gnome said:

I also can't help but notice you say nothing about circuit breakers.

Sorry didnt see that part in the question. 

1 hour ago, Gnome said:

I assume you know that an RCD doesn't provide over current protection.

No sorry I did not know that. I am use to ordering RCD's / RCCB's and RCBO's (Earth Leakages) with or without overload protection, depending on the application. With overload its normally just more expensive. When i use one without overload protection, I use a main breaker with it.  

Although we say RCD's we can refer to RCBO or Earth leakage , Chint have With or Without Overload protection. I am not sure which one Wisey has. 

[Wisey]

Geepers...thanks for the input everyone.

A helluva lot to digest and process and will do so over the next few days

As you can no doubt tell, I am dabbling here. So I ask you to please be patient with my knowledge base.

1) Thanks Gnome, I am aware of circuit breakers and the Earth leakage (I have) does not provide overload protection

2) Jaco I currently have 'without overload protection' so obviously in Eskom DB and Inverter DB will have a range of breakers (10, 20 and 40 Amp) allocated to the various circuits and the relative load/conductor diameters as per code specs. Some circuits (Stove and Inverter Utility are Eskom circuits and are 40Amp breakers)

3)  Thanks Plonkster for the detail, I will certainly get back to you asap. The pricing looks very reasonable.

Great guys have a fine evening. The full moon is rising clearly over the Indian ocean and its time to have a chow.

All the best

Wisey  

[Gnome]

On 2018/10/24 at 6:10 PM, Jaco de Jongh said:

 That is what I thought as well .. please read This.

And this is not the first time I experience something like this. 

 

The RCD was almost certainly damaged/broken out of the box.

It is a 50Hz sine wave, there is literally nothing in this world to distinguish it from Eskom power.

Again I'm assuming it is not being powered by a non-sine wave inverter because that for sure will make it heat up in some configurations.

[Gnome]

On 2018/10/24 at 6:21 PM, plonkster said:

RCD testers are like R250 :-)

Yeah you get some from eBay even cheaper than that where it essentially just connects a known resistor but obv. that means you need a voltage within a specific range.

Overall I agree getting a tester is probably the best option

But hax are possible if needed

 

On 2018/10/24 at 6:33 PM, Jaco de Jongh said:

Sorry didnt see that part in the question. 

No sorry I did not know that. I am use to ordering RCD's / RCCB's and RCBO's (Earth Leakages) with or without overload protection, depending on the application. With overload its normally just more expensive. When i use one without overload protection, I use a main breaker with it.  

Ah sorry that was more aimed to OP I actually assumed you did know about them but assumed he knew.

Whenever you have a RCD/Earth Leakage it must also be protected by over-current protection. Typically they were separate because of complexity and it also gave the freedom to split out multiple RCDs over multiple breakers.

But for the Inverter situation I use a single RCBO for the inverter output.

Edited October 26, 2018 by Gnome

[Wisey]

On 2018/10/24 at 9:27 AM, plonkster said:

There seems to be many issues muddled up together.

Yes, there are questions about the legality of connecting the Axpert's input to the grid, because it is unclear if the internal transfer switch inside the unit is SANS compliant. Technically this makes it illegal for grid connection even as a UPS.

You can however use another changeover switch on the output, and I found out yesterday that apparently this is what some installers now do (they use a simple ABB changeover contactor, which is technically not completely quite right either, but it is mechanically interlocking and has proper clearance gaps).

But the question relating to this legality is separate from the question of earthing, which I believe is rather the question about bonding earth and neutral while running from the inverter. The newer models can use the dry contact relay to switch another relay/contactor that establishes the bond when it disconnects the grid. If you have such a model, then it's a matter of buying some hardware and wiring it up.

If the bond is in place, then a downstream RCD will work correctly, as it operates only on the difference in current in the conductors.

I think this might be a good time to note that an RCD will work EVEN without the N-PE bond, it just takes significantly higher fault currents and/or multiple earth faults before it does. The reason you make the bond is to ensure that a single fault is sufficient to trip the RCD. Without the bond a single fault might go undetected until a second fault shows up.

Good morning everyone

Please assist with the following.

My query on the earthing issue now is 1) does the below apply to all makes of the Axpert inverter? 2) Does this prevent tripping of the Inverter EL (which I am having a problem with) - all circuits and loads have been tested as fault free. 

 

SuperDIY posted the following on this forum and I was wondering if anyone has experimented and had success with this:

Quote SuperDIY: "The most promising option looks like this:

1) Live and Neutral inputs on the inverter(s) need to be connected before the main ELR

2) All Earth connections on all inverters and inside all DBs needs to be bonded.

3) ELR must be connected on inverter(s) output.

4) To ensure that ELR on inverter output will protect against leakage currents the following needs to be done:

  4.1) The Main Switch in the Main DB (from where the inverter is fed, must not break the Neutral. The other option is to connect the inverter input Neutral to before the Main Switch in the Main DB to ensure that the Neutral Earth bond before then Main switch is always in circuit.

  4.2) The Neutral input and Neutral output on the inverter(s) need to be bonded."

Unquote

Look forward to your input

All the best

Wisey

 

 

[___]

39 minutes ago, Wisey said:

Quote SuperDIY: "The most promising option looks like this:

I remember that thread. It was a really long time ago :-)

A quick bit of theory.

1. In most homes earth and neutral will be connected together, that is "bonded". This is done in order to tie one end of the supply to ground potential, otherwise both ends might float several thousand volts "in the air". Bonding it means you know the one is at 0V and the other is at 230V. It also means that a single earth fault (a path between either conductor and earth, be it directly or through a person touching it) is enough to trip an RCD. Without the bond a single fault might go undetected.

2. The earth conductor is only allowed to carry fault current, there must be no "operating" current on this conductor. The current flowing in this conductor will be very close to zero most of the time, but all installations has a tiny bit of standing leakage, be it through current leaking through the insulation, or EMI filters and such in modern installations.

3. If you make a second bond somewhere in your installation, you create parallel paths from that point on, and it allows operating current to run on the earth wire from there. This is therefore not allowed. You should have one and exactly one earth/neutral bond in the system at all times.

4. Most houses have either a TN-S or TN-C-S earthing system. TN is for Terra(earth) Neutral, which means neutral and earth is bonded. The S means the earth conductor is separate. The extra C indicates that it is combined up to a point, and then separate. For a TN-S system, the separate earth conductor runs all the way back to the transformer. For TN-C-S you might have two conductors running into the premises, and then there will be an earth spike and a bond where it enters the premises, and from that point on the earth conductor will be separate.

5. Rules remain the same though, no extra bonds. Those make earth loops.

Now we get to the nitty-gritty of what happens at the inverter.

1. When the inverter is in bypass mode, the live and neutral on the output is directly connected to the live and neutral of the grid, and since that neutral is already bonded, you're done.

2. When the inverter is in island/invert mode, it opens the switch that connects L and N to the grid, and your neutral becomes unbonded.

3. One way to fix it is to bond earth and neutral on the inverter output (before the transfer switch, in other words inside the unit). This isn't done in the Axpert, and there is a reason for it.

4. The transfer switch in the Axpert is not double-pole on both sides. It has a double-pole on the grid side, but only a single-pole on the inverter side. The neutral of the inverter is never disconnected. I believe this is one of the reasons it fails SANS regulations, you're supposed to switch both legs. Because neutral is never disconnected, an extra bond in this position will create a second Earth/Neutral bond whenever the inverter is in bypass. So you cannot fix it this way.

5. In that old post you quoted, an easy way to get around it was quoted as simply bypassing the neutral switch on the grid side as well. This way the grid-side bond remains in place even when the inverter is in island mode. Of course this is also non-compliant, even if it does work.

6. The way other inverters do it, and also the newer Axperts, is they create a second bond only while they are in island mode, and remove it just before going into bypass. This is literally a relay between earth and neutral that is closed when the inverter disconnects the grid.

7. Axpert's do this by switching the "dry contact" relay inside. You are supposed to wire this to an external relay/contactor of a suitable rating to do the bonding. The bonding relay, in other words, is not built in.

All of this depends on your earthing system actually being TN :-)

[Wisey]

Hi Plonkster

Once again, thank you for the information. 

Yes, that post is 3 years old. 

Once again much to mull over and quite likely a few more questions to follow. Will offer some feedback and pics once complete.

All the best

Wisey

[flamegrilled]

On 2018/10/24 at 9:27 AM, plonkster said:

apparently this is what some installers now do

How do we know this is passing inspection?

[___]

2 minutes ago, flamegrilled said:

How do we know this is passing inspection?

I have no idea if it passes. I know the guy who supplies the ABB contactors to the particular installer in question (they sell a Axpert/battery combination package). I'm told that this is simple a DPDT changeover contactor that is normally used for lighting systems. It is mechanically interlocking in the physical sense, it is break before make by the same token, and it switches both Live and Neutral, so it is a step up from what the Axpert itself does internally. The gap is also large enough (I think, haven't looked at the specs). So it may pass... I simply don't know.

[flamegrilled]

3 hours ago, plonkster said:

ABB contactors

@plonksterThank you.

On the topic of earthing and earth spikes.

Can one have more than one.I assume 3 m apart and lots moisture surrounding it and at a dept of 3m?

I see a loosely connected earth cable on the Utility side box connected to the water supply(copper strap)

I cannot find an earth spike on the property? Could I purchase earth more spikes and sink it and link that to the house and the panels?

I still have metal electrical conduits in the roof.

 

[___]

21 minutes ago, flamegrilled said:

I see a loosely connected earth cable on the Utility side box connected to the water supply(copper strap)

I think that's just there to ensure that your copper piping is at the same potential, it's not an earth in itself.

22 minutes ago, flamegrilled said:

Can one have more than one.I assume 3 m apart and lots moisture surrounding it and at a dept of 3m?

I believe that is what electricians do if the resistance isn't low enough: They add more of them. Again... not an expert, just what I heard.

23 minutes ago, flamegrilled said:

I cannot find an earth spike on the property?

There might not be one. If the supply is TN-S, then you get your earth in a separate conductor from the transformer down the street.

 

23 minutes ago, flamegrilled said:

Could I purchase earth more spikes and sink it and link that to the house

Don't know. I think @pilotfish has stated in the past that he sees no problem with it, or hopefully this will summon him :-)

There are times when multiple earth points are allowed and it is called PME (protective multiple earth). Then there are other times people speak of a potential gradient (earth has resistance, a large current running through it such as a lightning strike creates a potential difference, which then shows up across the two earths and across the conductor). Overall my gut feeling is no: If you have a TN-S supply, don't sink your own. But it remains best to ask someone who knows more.

 

[flamegrilled]

On 2018/11/01 at 8:39 AM, plonkster said:

Most houses have either a TN-S

@plonksterThank you. I am assuming it is a TN-C-S earthing system. I can only see live and Neutral come up from the source to the MCB in the box in an armored sleeve.

I live in an area with overheads. I see 3 phases and a Neutral in the image.

[___]

1 minute ago, flamegrilled said:

I see 3 phases and a Neutral in the image.

Indeed. I'm out of my depth here. If I'm ever at the in-laws again (they have this arrangement too) I'll see if I can find the local earth spike. What I read on the topic says where the supply enters the premises, you will find an earth wire there and if you follow it you should find an earth spike.

On most houses in my area there is a big old removable cover on the other side of the wall where the distribution board and prepaid meter sits, and if you open it up, you usually find the big cable coming from the street. At my house, there are simply a couple of big wire nuts on it connecting it onwards into the DB... but if I had TN-C-S this is supposedly where I'd find a yellow and green wire snaking away towards something or somewhere...

[flamegrilled]

23 minutes ago, plonkster said:

the local earth spike.

@plonksterThe solar panels require earthing.I thought a new earth spike would do the trick.

[Jaco De Jongh]

1 hour ago, flamegrilled said:

I live in an area with overheads. I see 3 phases and a Neutral in the image.

@flamegrilled right on top of the pole is the 5th insulator with a wire barely visible, that is the supply earth. One of the reasons its installed above the others is to offer some kine of lightning protection. 

[___]

1 hour ago, flamegrilled said:

.I thought a new earth spike would do the trick. 

Again, I don't know. My preference is for the panels to have their own earth, so that lightening goes AWAY from the rest of the installation. But ask two different sparkies, they will argue for a bit, and then tell you to ask an engineer :-)

[pilotfish]

On 2018/11/02 at 4:02 PM, flamegrilled said:

The solar panels require earthing.I thought a new earth spike would do the trick

 

On 2018/11/02 at 5:51 PM, plonkster said:

Again, I don't know. My preference is for the panels to have their own earth, so that lightening goes AWAY from the rest of the installation. But ask two different sparkies, they will argue for a bit, and then tell you to ask an engineer :-)

So here is my opinion...

The short version is >>

Connect all earth terminals of EVERYTHING that has an earth terminal or requires earthing to your main municipal earth, using an earth wire of at least 1/2 the size of the main conductor, or 4mm for things that you are not sure of (TV antenna, sat dish, PV panels etc). After that do nothing because it is now earthed.

The long version >>

You have to be very sure of what you are doing to create a high quality earth using earth spikes. If you create a lousy earth, which you are almost certain to do, then you are creating more problems than you are curing.

Your municipal earth is probably 1ohm or less - it can be measured with an Earth Loop Impedance tester which is an expensive piece of kit, so either borrow one from a friendly electrician or pay your electrician to test it. It must allow double the amps of your main switch to flow in the event of a short circuit - so for a 60amp MCB it must allow more than 120amps to flow which would require an earth resistance of better than 2ohms in a 230V supply system.

I tried the spike route once at Cedar Lakes Estate where about a 200m long earth wire had been damaged in numerous places. Rather than digging up the entire estate I decided to go the earth spike route at the remote DB. The first spike gave me about 50ohms, the 2nd one dropped it to about 45ohms - five interconnected earth spikes later I was at about 35ohms - I guess about 100 spikes would have done it but by then I had decided that digging up the estate was looking like quite a good idea after all.

The problem with a poor earth connection is that it cant dissipate lighting currents which will cause earth voltage in the vicinity to rise massively - now you have a 300 kilovolts in the vicinity of your one lousy earth spike and 0 volts on all your correctly bonded equipment, and a lot of stuff converted to smoke in-between (I hope that you are not one of them).

[pilotfish]

Note that the above applies to a stand-alone earth spike - if you want to surround your home with earth spikes that are all connected back to your main earth terminal then that is all good.

[Wisey]

On 2018/11/02 at 5:51 PM, plonkster said:

Again, I don't know. My preference is for the panels to have their own earth, so that lightening goes AWAY from the rest of the installation. But ask two different sparkies, they will argue for a bit, and then tell you to ask an engineer

Agreed. The roof is aluminium corrugated. The corners will all be lightning protected by bonding to 1m copper earth spikes/rods, driven down to approx 1,5 metres. Panels and Combiner box earth bonded to those. This earth seperated from the AC side (Inverters and Eskom) for reason you point out above.  Unfortunately do not have an earth tester to measure the resistance. Relying on my outstanding relationship with Mother Nature for assistance with the objective risk.

[___]

9 hours ago, pilotfish said:

Connect all earth terminals of EVERYTHING that has an earth terminal or requires earthing to your main municipal earth, using an earth wire of at least 1/2 the size of the main conductor, or 4mm for things that you are not sure of (TV antenna, sat dish, PV panels etc). After that do nothing because it is now earthed.

Thanks for the concise answer. Also for the longer one, which explains it so well in humourous fashion.

The old farmer trick was to drive a long pipe into the earth in an area that tends to be wet a lot of the time... but it was never actually measured and done by the book. Makes you think...