Help with solar pv polarity

[Algarve Sparky]

So I have completed a rewire on a house that had stood empty for several years, vandals had stripped the place including pulling all of the cables from the tubes.

So rewire was a case of replacing cables, board, sockets and switches.
However the place is no longer connected to the electricity grid and the new owner had a €20k solar system, inverter and a rack of 9 batteries installed even before we turned up.

My question, the solar guys cabled everything up and as we were starting supplied us a feed from the inverter, we connected into our new board and as circuits were pulled in we connected them, tested and carried on.

Its all up and running now but I cannot for the life of me get my head around why the Neutral in the house seems to be the live phase ( volt stick ) and on a meter get 240v between Neutral and earth nothing between live and earth ( via ground rod )? if I switch the cables around the issue remains ?? the output from the inverter seems to always want the neutral side of our board / cabling to be the live what ever way the output is connected.

It feels very odd and now we have a back up generator to bring on line which will auto start if the inverter sees the solar charge low as well as the batteries, how can I know which way to align the phase output from the generator and the solar?? ...help guys

 

[marconi]

So I have completed a rewire on a house that had stood empty for several years, vandals had stripped the place including pulling all of the cables from the tubes.

So rewire was a case of replacing cables, board, sockets and switches.
However the place is no longer connected to the electricity grid and the new owner had a €20k solar system, inverter and a rack of 9 batteries installed even before we turned up.

My question, the solar guys cabled everything up and as we were starting supplied us a feed from the inverter, we connected into our new board and as circuits were pulled in we connected them, tested and carried on.

Its all up and running now but I cannot for the life of me get my head around why the Neutral in the house seems to be the live phase ( volt stick ) and on a meter get 240v between Neutral and earth nothing between live and earth ( via ground rod )? if I switch the cables around the issue remains ?? the output from the inverter seems to always want the neutral side of our board / cabling to be the live what ever way the output is connected.

It feels very odd and now we have a back up generator to bring on line which will auto start if the inverter sees the solar charge low as well as the batteries, how can I know which way to align the phase output from the generator and the solar?? ...help guys

Please tell me the details of the inverter.

 

[Algarve Sparky]

Please tell me the details of the inverter.

See attached the inverter details, I realised after writing this the back up generator issue was not a problem as it connected to the input side of the inverter so that parts is up and running so happy with that, the polarity issue remains the same though.

 

[marconi]

I need the make and model number please.

 

[Algarve Sparky]

I need the make and model number please.

Axpert VM III 5kw Hybrid Inverter - Cellcronic

Axpert VM III is a third-generation off-grid hybrid inverter that comes with company fitted battery wire and AC DC Distribution Box. Its detachable LCD control module can be turned to a remote panel. It’s also integrated with Bluetooth interface ready for mobile monitoring and supports USB...

cellcronic.com

 

[marconi]

Thank you. I will read up on this inverter today.

 

[Algarve Sparky]

Thank you. I will read up on this inverter today.

Thanks buddy

 

[marconi]

Are lightning surge protectors connected between array dc cables and earth electrode?

is inverter chassis box connected to earth electrode?

Are frames of solar panels connected to earth electrode?

what type of panels?

what potential differences exist between live ac or dc conductors and earth electrode when you use an approved voltage tester AVT rather than volt stick or multimeter?

This hybrid inverter is a transformerless type which means there is no galvanic isolation between the dc and ac circuitry. There will be inevitable ac and dc leakage currents to earth which will in combination determine the potentials of the dc and ac conductors with respect to earth.

I have found the manual for the inverter to read and will be in touch later or tomorrow. The AVT test results would be helpful if you can do it.

 

[pc1966]

A quick look at the manual says this:

11. GROUNDING INSTRUCTIONS -This inverter/charger should be connected to a permanent grounded wiring system. Be sure to comply with local requirements and regulation to install this inverter.

However, it is not clear if they are referring to the chassis (which should obviously be grounded) or the AC neutral line which is (by the definition of "neutral") grounded at some point, with that point being the definition of the TT/TN-S/TN-C-S sort of earthing arrangement.

I don't know the rules in Portugal, but in the UK you are only allowed to have a single connection between neutral and earth, and that is always done by the DNO (power supply company) for any mains power, or if you have a sizeable backup generator then you would do it there but you must have a transfer switch that switches neutral as well as the line conductors so the N-E link is always outside of your installation and at the source of power.

My suspicion then is it relies on the incoming AC supply's neutral as a means of grounding for the resulting AC from the battery/solar source, so in the absence of a grid supply that ought to be grounded via a suitable rod, but I suspect you might have to ask the manufacturer of the inverter.

 

[marconi]

Are lightning surge protectors connected between array dc cables and earth electrode?

is inverter chassis box connected to earth electrode?

Are frames of solar panels connected to earth electrode?

what type of panels?

what potential differences exist between live ac or dc conductors and earth electrode when you use an approved voltage tester AVT rather than volt stick or multimeter?

This hybrid inverter is a transformerless type which means there is no galvanic isolation between the dc and ac circuitry. There will be inevitable ac and dc leakage currents to earth which will in combination determine the potentials of the dc and ac conductors with respect to earth.

I have found the manual for the inverter to read and will be in touch later or tomorrow. The AVT test results would be helpful if you can do it.

 

[marconi]

Further to my last question on type of panels: The manual says this:

WARNING: Because this inverter is non-isolated, only three types of PV modules are acceptable: single crystalline, poly crystalline with class A-rated and CIGS modules. To avoid any malfunction, do not connect any PV modules with possible current leakage to the inverter. For example, grounded PV modules will cause current leakage to the inverter. When using CIGS modules, please be sure NO grounding.

 

[marconi]

With the inverter completely disconnected ( L and N) from the main board, measure the insulation resistance of the house installation L-cpc and then N cpc - all house appliances disconnected/turned off and light switches off/lamps removed - cpc connected to earth electrode for these two tests. if you can remove all lamps do tests with light switches on.

It could be there is low IR L-cpc/earth compared with N-cpc/earth. When connected to Board the floating L and N from the inverter output will assume potentials with respect to earth dependent on the magnitude of the IR to earth - higher IR to earth will have higher potential to earth.* That the higher potential is always on the N side suggests low IR somewhere on the L side of house wiring. Or may be a faulty appliance with low IR in the same way.

* (The two house IRs form a potential divider connected across house wiring L and house wiring N with the midpoint connected to earth). So same result if output of inverter swapped over.

 

[Algarve Sparky]

Okay so the main grid network is totally absent, vandals took the cables across the field years ago, so there is no power, neutral or earth via the power company.

So the solar panel company basically fitted it all up and cabled to our board ( we connected it ) with a live neutral and earth ( maybe)

The solar company was a contractor from 250 miles away and they fitted it up, got paid and left never to return.
We looked through the system to help the client and determined the solar panel frames are earthed back to the inverter earth point, from this point the battery cases are earthed, from the same point is the cable they left for us to connect into the new board.

So we wired the house, as if it was connected to the mains network but basically the ouput from the solar is wired into the main trip ( single phase )

We ran a 16mm earth cable outside and placed 2 x earth rods set 5 meters apart, this also was connected in at the board.

We wired the back up diesel generator into the 230v input at the inverter and connected the auto start lead between the two.

The system works, came on line just fine, charges the batteries and supplied the whole house, one day whilst working there we let the batteries go low ( covered the solar panels) and late in the day the generator started up and perfect the batteries started to charge and the house was still powered.

So the only fly in the ointment as were is the polarity issue ?

Interestingly when we opened the inverter up the live and neutral outputs were connected the wrong way around, aha I thought, but no it made no difference correcting them, makes me think they were trying to solve the issue too??

Oh and there are no lightning arresters fitted, to be honest the whole solar pv panel thing here is very badly serviced, generally by wannabes who have jumped on to the band wagon as such, I am not wanting to get into it as we have plenty of work anyhow but as a spark I should get a working knowledge of it really.

Thanks in advance for any advise.

Ps will try a volt check between the ac and dc with my Martindale meter

 

[marconi]

Assume IR readings are 1MOhm and 22MOhm as shown in attached diagram then Neutral will always be 220V wrt to earth and Line 10V wrt to earth, even if inverter output swapped over.

You probably see same thing when generator powers home if its output is floating.

Be mindful that many white appliacnes like washing machines have mains electromagnetic interference suppression filters which connect across L, N and E so these need to be unplugged for IR tests. It is not unknown for these to fail but we can consider that later if necessary.

 

[Algarve Sparky]

Assume IR readings are 1MOhm and 22MOhm as shown in attached diagram then Neutral will always be 220V wrt to earth and Line 10V wrt to earth, even if inverter output swapped over.

You probably see same thing when generator powers home if its output is floating.

Be mindful that many white appliacnes like washing machines have mains electromagnetic interference suppression filters which connect across L, N and E so these need to be unplugged for IR tests. It is not unknown for these to fail but we can consider that later if necessary.

That is what I wanted to hear, good to get it right in my head, I have spent the last +5 years getting my UK electrical practises converted to Portuguese ways yet still keeping safety and quality in mind, way too many builders here do electrical installs!

On the whole I like it, tubing houses from boards to every socket and switch makes for great / easy rewires.
Most of the commercial work we do is almost the same as UK but Solar, Omg I have seen some terrible work.

Thanks for you input and the sketch, very much appreciated.

 

[marconi]

There remains the question about whether to continue with floating ac lines viz L1 and L2 or whether to connect one L2 to local earth to produce L and N. As this home is off-grid and not serviced by a mains electricity supply the first step I think is to find out what the Portuguese wiring regulations say for sites with two sources of non-grid mains supply. I don’t get involved much with foreign wiring systems because I don’t know what I don’t know.

There will be others in the EF who can advise you should you wish. If most dwellings are earthed neutral then I would see advantage in making this place the same to avoid a surprise to electricians in the future and the use of single pole protection and switching accessories. Most home appliances assume LN not floating L1 and L2. The thinking required is where and how to make the L2 of the gennie and the inverter into an N. Some signage would be needed.

I stand ready to assist further with the polarity query.

Happy New Year. Please follow up and pictures are always enjoyed.

 

[Algarve Sparky]

Thank you again for input, as it happens I have a call back tomorrow as the client has a further issue arisen over the New year holiday.

His message reads

"Hi Jeff,
Have a strange issue when the geni is on and the inverter panel is show the two 230v inputs, as we use more power the 230v starts to reduce going as far down as 189v and then the geni built in trip activates "

Not sure what he means exactly so will go and look for myself and report back here what I find.

Thanks

 

[pc1966]

That sounds a lot like the generator is overloaded so its volts are dropping, but it might also be some feed-through limit of the inverter if it is acting like a UPS (i.e. input from PV and/or generator goes to battery first, and from there is converted to AC output).

Do they have any metering to show what demands they are placing on the system?

 

[marconi]

https://gbc-solino.cz/wp-content/uploads/2020/03/Axpert-VM-III_manual-20190201.pdf

(Re #18: The inverter display can show 230V ac power output).

When the inverter uses the utility input - in this case fed from the gennie - it is in bypass mode such that the utility input is connected to the output by a fast transfer switch. You can tell the power inout/output mode of the inverter by looking at the state of the LED lights and referring to page 13 of the inverter manual at link above.

The total power drawn from the gennie is not just the 230V ac output load; it also includes battery charging if this has been selected using the general setting - see page 16 onwards.

Please confirm first what is the power output priority - PROGRAM 1 page 16. I expect it to be SbU.

Now back to battery charging. The maximum utility (ie gennie derived) charging current can be preset - see page 18. If for example the maximum utlity charging current is 40A then the power required from the generator is 48V x 40 = 1920W or nearly 2kW. Depending on the state of the battery's charge, there may be times when the remaining power available from say a 2.8kVA gennie for the house load is only 2.8 - 2 = 0.8kW. As the battery charger progresses through its charging routine the charging current will reduce over time until it is only a nominal trickle current - then the full output of the gennie is available to power the house load. The gennie can the n be easily overworked if the battery is in a low state and the house load is high at the same time.

When you visit next, find out the kVA of the gennie and then have a look at PROGRAM 11 see page 18 and discover the maximum utility charging current. Also look at PROGRAM 2 page 16 to discover what is the total solar plus utility charging current limit.

What you can do to free up more power from the gennie is reduce the maximum utility charging current . Of course the battery will take longer to charge. In the applications I have used hybrid inverter with 3.4kVA gennie input I selected a charging current to produce 0.5kW - in your case a current of 500/50 = 10A - for a maximum load power of circa 1.5kW and a margin of 1.4kW to deal with fridge/freezer starts.

I hope this makes some sense. Please provide some numbers for the charge currents if you wish further help and gennie kVA and type.

 

[Algarve Sparky]

Sorry for slow reply, been flat out with installs, the generator problem has been resolved, the two core remote cable to start the genny automatically when low on sun load and low battery had an issue ( pulled in an underground tube 30 metres from the house ).

Still ongoing issues but not back on site till next month, the solar company still will not come back !