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Advice please: Hooking up battery backup to main DB


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Hi,

I'm in the planning stages of a DIY UPS backup system for our house, and I would like to ask your advice please. At some stage I will add solar, but for now I just want battery backup for the essential loads.

The plan is as follows:

1) Replace the 60A grid isolator in the DB with a 60A transfer switch.

2) Connect the one input of the transfer switch to the grid

3) Route grid power to the AC input of a Victron Multiplus II 5kVA inverter (hooked up to a couple of Pylontech batteries) in the garage.

3) Route the "non essential loads" output of the Victron back to the other input of the transfer switch.

4) Remove all essential loads from the main DB and connect them to the "essential loads" output of the Victron in a new DB in the garage.

My questions are:

1) Are there any glaring problems (safety and regulatory) with this plan?

2) Is it allowable to use 16mm^2 wire for live and neutral and 10mm^2 (or less?) for earth between the inverter and main DB, or must everything be 16mm^2?

3) Is it allowable to put both AC pathways between the inverter and main DB in the same conduit?

I'm an electrical engineer by training, but I am ashamed to admit that I have no practical experience and my knowledge of the electrical codes is limited. (I've been in software development ever since leaving university 20 years ago).

Thanks for your help!

Pierre

 

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On 2020/02/15 at 3:30 PM, PierreJ said:

I'm an electrical engineer by training, but I am ashamed to admit that I have no practical experience and my knowledge of the electrical codes is limited.

I have two software degrees! I'm far less qualified 🙂

On 2020/02/15 at 3:30 PM, PierreJ said:

1) Replace the 60A grid isolator in the DB with a 60A transfer switch.

Make sure the installation has overcurrent protection. In most modern installations the "main switch" is also an overcurrent protection device. If it is, you cannot just replace it with a change-over that has no such protection.

Additionally, I still have a gut feeling that won't be allowed, because it breaks what I might call the rule of common expectations. Most people expect the power to be off if the switch is down. With a changeover this won't be the case. Usually you need a main switch for the inverter, a main switch for the grid, and a changeover between the two. Both main switches have to marked and when they are off the installation must be unpowered.

On 2020/02/15 at 3:30 PM, PierreJ said:

2) Is it allowable to use 16mm^2 wire for live and neutral and 10mm^2 (or less?) for earth between the inverter and main DB, or must everything be 16mm^2?

The earth wire must be able to carry the full fault current, which basically means it need to be sized large enough to take whatever the main breaker can throw at it, 60A in this case. It would be best to size it the same as the live and neutral wires.

On 2020/02/15 at 3:30 PM, PierreJ said:

3) Is it allowable to put both AC pathways between the inverter and main DB in the same conduit?

Yes.

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My advice to you ...if you interfere with the integrity of the electrical installation anyway ...make sure you have a mate who can inspect and pass the modification/backup system...or contact your local sparkie and ask him to oversee the project and test and issue a COC when completed. 

I am not going to go into details ...but what i will tell you... if you doing "off grid"  DIY solar...inverter installations etc and you dont interfere with the integrity of the electrical installation in anyway ...that's is one thing ...as soon as you link the system into the property electrical installation...make sure you understand all the SANS 10142 regs and are aware of the consequences...it is no longer a DIY project..

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23 hours ago, Pietpower said:

Don't know the Victron inverters but I think you normally add a circuit breaker to DB1 to feed the inverter and the inverter then feeds DB2 with your essential loads.

What I've done in the past, and seen others do, is you feed DB2 from DB1. You must have an isolator in DB1 so you can issolate DB2. Then as per regulations you stick a big notice on DB2 that shows it is fed from the main DB.

Then in DB2 you put a changeover switch. The one side of the changeover is fed directly from the supply that comes from DB1. You also feed the input of the inverter from here (through an issolator that disconnects both L and N, and must have overcurrent protection).

The other side of the changeover switch is fed from the inverter output. Again, through a breaker that allows you to isolate and has overcurrent protection.

Then the common side of the changeover feeds an RCD... and then your backup circuits feed from there.

Edited by plonkster
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1 hour ago, Pietpower said:

The changeover in DB2 will transfer loads to the inverter

By changeover I mean one of these:

Selection_473.png.b1d428cb10804d17427d7ca9a24edb85.png

1 hour ago, Pietpower said:

What reasoning do you feed the backup circuits in DB2 from DB1 as opposed to feeding via the inverter unit?

Because I need somewhere to put the changeover. Given that space is usually constrained in DB1, which is why people do this stuff in the first place, it just makes more sense 🙂

Edit: Just to be clear, I do feed DB2 via the inverter. The changeover is left in the "inverter" position during normal operation, and the AC power from DB1 only makes a short "stop over" in DB2 in order to 1) connect to the grid side of the changeover switch and 2) to put in an additional breaker to protect the input cable of the inverter.

The idea is that it should be possible to issolate the inverter completely without leaving DB2 without power.

 

Edited by plonkster
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On 2020/02/23 at 9:03 AM, plonkster said:

Make sure the installation has overcurrent protection. In most modern installations the "main switch" is also an overcurrent protection device. If it is, you cannot just replace it with a change-over that has no such protection.

Where the grid power enters the DB there's a 60A breaker on the live wire followed by the L+N isolator. Not sure why there's both a breaker and an isolator, because the isolator also has overcurrent protection. The 60A breaker is humongous compared to all the other breakers, and is also rated at 6kA (whereas the isolator and all the other breakers are 3kA), so perhaps whoever installed it liked the idea of the extra protection.

 

On 2020/02/23 at 9:03 AM, plonkster said:

Additionally, I still have a gut feeling that won't be allowed, because it breaks what I might call the rule of common expectations. Most people expect the power to be off if the switch is down. With a changeover this won't be the case. Usually you need a main switch for the inverter, a main switch for the grid, and a changeover between the two. Both main switches have to marked and when they are off the installation must be unpowered.

Good point. I have severe space constraints in the main DB, so I will have to get creative to fit all the stuff in.

 

On 2020/02/23 at 9:03 AM, plonkster said:

The earth wire must be able to carry the full fault current, which basically means it need to be sized large enough to take whatever the main breaker can throw at it, 60A in this case. It would be best to size it the same as the live and neutral wires.

The current earth coming in from the earth spike is 10mm^2 and the live and neutral are both 16mm^2, but I have enough experience working with electricians to know that just because it is currently like that doesn't make it legal. It poses another challenge for me though, and that is how I'm going to fit  3 x 16mm^2 wires through a 20mm gland. (2 x 16mm^2 and 1 x 10mm^2 is already a very tight fit.)

 

Thanks for the help.

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On 2020/02/23 at 10:51 AM, Pietpower said:

Why do you want to install a changeover/transfer switch if you are installing a new DB (call it DB2) for all the essential loads.?

Do you feed the inverter from the grid direct or from DB1?

The grid enters the house in DB1, so I don't have much choice - I have to route power from DB1 to the inverter. 

 

On 2020/02/23 at 10:51 AM, Pietpower said:

Don't know the Victron inverters but I think you normally add a circuit breaker to DB1 to feed the inverter and the inverter then feeds DB2 with your essential loads.

If you feed the inverter from DB1 then the inverter feed back to a transfer switch it sounds like you are creating a loop connecting the output of the inverter to the input?

I want to run the non-essential loads from the second AC output of the inverter, so if the grid is up and the sun is shining that I can also use solar to power the non-essential loads. I could leave the non-essential loads before the inverter (i.e. not loop back the inverter output to DB1), but then I would have to install a current meter in DB1 for the inverter to know how much power the non-essential loads are using. I don't want to feed in power to the grid.

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8 hours ago, isetech said:

My advice to you ...if you interfere with the integrity of the electrical installation anyway ...make sure you have a mate who can inspect and pass the modification/backup system...or contact your local sparkie and ask him to oversee the project and test and issue a COC when completed. 

I am not going to go into details ...but what i will tell you... if you doing "off grid"  DIY solar...inverter installations etc and you dont interfere with the integrity of the electrical installation in anyway ...that's is one thing ...as soon as you link the system into the property electrical installation...make sure you understand all the SANS 10142 regs and are aware of the consequences...it is no longer a DIY project.

Thanks for the advice. Initially I just wanted to pay someone for all the hardware and the installation and be done with it, however with the current loadshedding situation I've been finding it difficult to get installers to even quote me. The couple of quotes that I have managed to get so far don't seem reasonable to me. The hardware prices are at least 20% higher than what I can get myself as a member of joe public (I assume installers get a discount?), and I've been quoted labour charges in excess of R45k. Now I don't begrudge anyone trying to make a living, but we're talking big numbers here.

 

So the current plan is to buy the hardware and to install most of it myself in an entirely off-grid fashion, and then to pay someone to fix any mistakes that I've made, to hook it up to the grid, and also do all the paperwork with CoCT. I'm going to do the solar panels in 2S2P blocks and join the blocks up at the inverter, so the DC voltage on the roof will be less than 100V and I probably won't electrocute myself. I do have one big concern, and that is that I won't be able to find someone willing to sign off on a system that they did not install themselves.

 

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5 hours ago, PierreJ said:

Good point. I have severe space constraints in the main DB, so I will have to get creative to fit all the stuff in.

Hager makes a 32A double-pole DIN-mount breaker that fits in a single space. Unfortunately nothing larger, but for the inverter main switch (where 32A might be ample), it saves space if you use that one.

Also, regarding the earth cable and the others, you could install a lower-rated breaker for the sub-DB. If you install a 40A breaker, for example, you can use 10mm^2 wire without a problem. A 40A supply for circuits that are deemed "essential" and are inverter-powered during an outage... should be more than ample.

Another way to gain some space, since you already noted that it has a humongous 60A breaker in it, is to replace that with a single combination breaker. For example, for Samite rail there is the CBI QA-N-2(13) breaker, which is an issolator with overcurrent protection, 26mm wide. For DIN-rail, the aforementioned 32A Hager is the smallest form-factor I know of.

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9 hours ago, plonkster said:

Hager makes a 32A double-pole DIN-mount breaker that fits in a single space. Unfortunately nothing larger, but for the inverter main switch (where 32A might be ample), it saves space if you use that one.

My main DB is Samite, but I will definitely not be making the same mistake again, and the sub-DB will be DIN. So far I have been unable to find a Samite transfer switch, so it llooks like I'm going to have to use those wobbly Samite to DIN clips to get a transfer switch in there.

 

9 hours ago, plonkster said:

Also, regarding the earth cable and the others, you could install a lower-rated breaker for the sub-DB. If you install a 40A breaker, for example, you can use 10mm^2 wire without a problem. A 40A supply for circuits that are deemed "essential" and are inverter-powered during an outage... should be more than ample.

I would like to put all the loads (essential and non-essential) after the inverter, so I don't have to hassle with an external power meter. The 5kVA Multiplus can transfer up to 50A from input to output, and adding the 15A CoCT generation limit gets me up to 65A. I could route the earth cable separate from L+N. Is that legal?

I guess I should just bite the bullet and shell out the R1000 for SANS 10164. It just seems wrong to me that one should have to pay for access to a national standard, particularly one regarding safety.

 

9 hours ago, plonkster said:

Another way to gain some space, since you already noted that it has a humongous 60A breaker in it, is to replace that with a single combination breaker. For example, for Samite rail there is the CBI QA-N-2(13) breaker, which is an issolator with overcurrent protection, 26mm wide. For DIN-rail, the aforementioned 32A Hager is the smallest form-factor I know of.

Thanks, I will check it out.

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3 hours ago, FixAMess said:

Can you please provide a pic of what the official sticker/signage looks like? My local elec shop says he is not aware of this sticker.

It seems to be a new thing. When I recently sold my house, the electrician labelled the DBs with a label maker. The main one has a label saying "FED FROM OOSTERSEE BOX" and the sub-dB has a label "FED FROM MAIN DB". At my son's school I've seen similar labeling on DBs indicating where they were fed from, so naturally I assumed this is now regulation.

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On 2020/02/25 at 10:29 AM, FixAMess said:

This is  the BIG problem....It seems nobody wants to sign off on a system they did not install themselves....

Its simple you contact an electrical inspector who specialises in COC's ...tell him you are selling your house and need a COC for the sale ...if you do it this way ....you not only get the backup system signed off ...you also get a COC for the rest of the house... provided the house is up to standard...otherwise an inspection report is carried done and a list of all the repairs required is issued with a quote to repair.

A backup system cannot be signed off unless there is a valid COC for the rest of the house... so either way you actually need a COC for the entire property in any case.

People do this all the time... they get a builder and his HAR (hit and run) contractors to complete a project ...then the owner contacts an electrical inspector  and tells him that the property is up for sale...COC is done for the entire house including the new installation and modifications if up to standard.

 

 

 

Edited by isetech
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On 2020/02/25 at 10:16 AM, FixAMess said:

Can you please provide a pic of what the official sticker/signage looks like? My local elec shop says he is not aware of this sticker.

The DB must be clearly labelled...the more info the better for everyone ...especially the people living in the house. 

The DB name.

Where it is fed from. 

You could put the size of the supply cable (optional) 

Identify each switch and circuit breaker. 

"in case of accidental leakage switch off the main switch" in 11 official languages is required (just kidding only english and afrikaans) 

 

 

 

 

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Ok, so I have come to the realisation that it's just not going to work to try and make space in the main DB in the kitchen to add changeover switches and whatnot. So what I'll have to do is to route the Eskom power from the main DB to the inverter DB in the garage, do what I have to do in the DB there and then route power back from the inverter to the main DB.

So the plan is to put in a 60A 2 pole isolator on the Eskom live and neutral in the main DB and call it "Main Switch (From Eskom, To Inverter)". The output connects to the inverter DB in the garage. In the garage I will have my surge protection, changeover switches, etc. The non-essentials output of the inverter I then route back to another 60A two pole isolator in the main DB called "Main Switch (From Inverter)". The earth leakage and all the loads in the main DB will connect to this second isolator.

Now the question is: Will this pass a CoC check? Do I need indicator lights or some kind of physical separation between the two isolators (for which I don't have space)?

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15 minutes ago, PierreJ said:

 The non-essentials output of the inverter I then route back

Your cable costs are going to be significant. I don't know how far you have to go with this rerouting, but at 60A and over some distance, we're talking some proper cabling.

In cases like this I advise people to install the energy meter in the main DB (for single phase that would be the ET112, which takes up only 64mm or two DIN spaces). Then all your non-essential loads are powered directly and not via a long detour, and you only need to size the cabling going to the garage for whatever current it will carry. The cost of the energy meter is  made up for in lower cable costs (an RJ45 cable to carry the RS485 comms is much cheaper).

Is there really no way to mount a sub-DB close to the current main DB?

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54 minutes ago, plonkster said:

Your cable costs are going to be significant. I don't know how far you have to go with this rerouting, but at 60A and over some distance, we're talking some proper cabling.

In cases like this I advise people to install the energy meter in the main DB (for single phase that would be the ET112, which takes up only 64mm or two DIN spaces). Then all your non-essential loads are powered directly and not via a long detour, and you only need to size the cabling going to the garage for whatever current it will carry. The cost of the energy meter is  made up for in lower cable costs (an RJ45 cable to carry the RS485 comms is much cheaper).

Is there really no way to mount a sub-DB close to the current main DB?

Fortunately the wiring distance between the two DBs is only about 10m, so at roughly R30/m for 16mm^2 wire I'm looking at about R1500 (2 x 10m live, 2 x 10m neutral and 1 x 10m earth), which I can live with.

My main DB is also Samite, so I would have to use those adapter clips for DIN equipment which looks bad. Furthermore I would like to have the option of switching the entire main DB between being an essential and non-essential load. I had our energy usage monitored over a month and we rarely go over 4kW (about 1 hour per week), so I might get away with hooking up the entire house to the essential loads output of the Multiplus. The Multiplus can sustain 4kW from battery and/or solar, and when there's Eskom power I can draw an additional 15A from the grid on top of that. When the grid is down and the sun isn't shining we would have to manage the loads.

In any event, are there any regulatory issues with routing power from the main DB to elsewhere and then back in the way that I am planning? Do I need power indicator lights? Would it complicate matters if I perhaps split loads in the main DB between Eskom and the Inverter output? In case things don't work out I might want to move the geyser directly to Eskom power (but then I'll also have to add an energy meter of course). I just don't have any space in the DB and on top of that some of the loads in the main DB are essential and others not. It being Samite is just the cherry on top.

Edited by PierreJ
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