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Inverter Connection to DB - Help needed


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Hi, 

I have an Axpert 5KVA inverter that I want to connect to the DB board to run the lights and plugs. It was installed at my previous place and was pretty straight forward (Output and Input of 220 volt and then DB board connections, nothing was connected in between, this is how I inherited it and worked flawlessly for 3 years.) , however I have requested several quotes from various electicians and its nearly more to install than to actually buy the system. (pricing is around the 8 - 10K for the installation and parts ) 

My question revolves around the connectivity of the Inverter to the grid and also the batteries. It seems all electricians build in manual cut over switches between in the inverter and the grid, which they argue is to protect the inverter or grid connection as well as surge protectors

The other is a fuse box between the batteries and in the inverter for the same reason, but I am not sure how there can be an overload/short between the batteries if they are connected correctly in series. (4 x 90ah deep cycle lead/acid). 

Ultimately however if this is the correct way, then I will head that advice, or the advice of the forum as I am not an electrician and get the parts from Communica or similar and potential build that system myself as I have a bit of an issue paying huge labour and parts costs for a pretty straight forward process. 

As always, thanks for the advice in advance. 

 

 

 

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Hi,

Connection to your DB all depends on the space available within your current DB. 

Inverter AC Input:

There should be a seperate circuit breaker feeding the inverter.  This circuit breaker is normally connected straight to the mains CB and is not connected to the Earth Leakage.  Surge Protection is highly advised.

Inverter AC Output:

This is highly dependent on the space available in your current DB.  The output from the inverter should feed into a main CB rated accordingly to your cable size and inverter output current.  From the main CB you should have a second earth leakage.  From the Earth Leakage you then supply power to the individual CBs for the circuits you wish to power.  In most cases the DB doesn't have sufficient space for the additional mains CB, surge protection and earth leakage.  This would then require you to install a seperate sub-db specifically dedicated to the inverter output circuits.

Manual Change over switch:

Highly advised to install a manual change over switch.  This would allow you to change over the AC output should the inverter requires maintenance or replacement.

Battery Fuses:

It is highly advised to install battery fuses.  This protects your cables and batteries from the overcurrent and shortage situations.

Please familarize yourself with the SANS specifications as you will have to comply in order to obtain a COC

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1 hour ago, Bloubul7 said:

Inverter AC Input:

There should be a seperate circuit breaker feeding the inverter.  This circuit breaker is normally connected straight to the mains CB and is not connected to the Earth Leakage.  Surge Protection is highly advised.

I'm no expert but I would've thought that the feed to the inverter should be protected by the earth leakage too?
My grid feed comes into the DB to the earth leakage first, then to an isolator, then on to the usual CBs, that's how it was from when we moved in. Personally I would bring the grid feed into an isolator and then to the earth leakage, but I'm not an electrician so just making an assumption...

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4 hours ago, javadog said:

manual cut over switches

The Change Over switch is not a requirement, but it does make things much easier if you want/need to switch off the inverter (batteries replacement, inverter fix, etc.) In a scenario where you do not have this switch and there is any problem, you will not be able to power the lights/plugs until you rewire it to bypass the inverter. If you have the switch, then you just flip it to bypass the inverter and all can continue. They cost about R300-R800 depending on the brand and where you buy them.

 

4 hours ago, javadog said:

fuse box between the batteries

This is not optional. The fuse is the same safety device as a Circuit Breaker (CB is a fuse you can reset). They protect your cables from too much power flowing through so that the cable does not heat up, melt and start a fire. The reason we use fuses for the battery connection is that CB for the amps that the batteries give is just too expensive. Make sure it is a DC fuse with an Amp rating that is below what your battery cable can handle. (Normally this will be a 125A 56V fuse - they go for R500-R700 including a fuse holder)

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Hi Every one 

Thank you for the feedback!!!

 so from what I understand. 

Outgoing: I will need to add a CB into the DB board connect that the Inverter ( take a connection from earth to 'power; that and then remove the other connections to lights and plugs)

Incoming: I will need a CB which runs into an earth connection and from there powers the various other CB (Lights + Plugs) 

Batteries: I will need to buy a place a fuse box between batteries and inverter to protect that connection. 

Manual override switch ultimately is optional but would be between the outgoing connection between DB and inverter and incoming.

If I understand this correctly, I will basically be creating a loop from DB -> outbound -> Switch ->  Inbound as opposed to

DB -Outbound - -> Inverter  -> inbound.

And now lets hope it all fits, below is an image of my db board. The first breaker to the right of earth is the geyser, the rest are lights and plugs, stove is gas and oven has its own breaker not on the board.

 

 

DB Board.jpg

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The neutral for your inverter must also be connected before the Earth Leakage otherwise the EL will trip when it notices an inbalance between the live and neutral. 

The neutral from your inverter output should go into a seperate neutral bar

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 Good day to all you fantastic guys that have replied  to this question .  As they say a picture is worth a thousand words can any one supply a single phase wiring diagram.  It does not have to be fancy any  well labeled / description of the components on hand draw diagram would be great . It does not have to show the whole DB board  just the basic inverter connections with change over switch  and required circuit breakers A snap shot with you phone will be magic . Many thanks in advance Regards Gordon..

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Here's a basic diagram of my layout.
image.thumb.png.56248c94741cf577b7f86091f59231b3.png

I found out that it's crucial to have the inverter input feed from before the utility side earth leakage (RCD) else the RCD keeps tripping.
I put the inverter load output RCD before the change-over switch, just to avoid having 2 RCDs when changed over to utility, it's not normally a major issue though as far as I know...
The top of the following post has quite a nice diagram of the wiring setup...

 

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On 2020/08/12 at 3:01 PM, Louisvdw said:

This is not optional. The fuse is the same safety device as a Circuit Breaker (CB is a fuse you can reset). They protect your cables from too much power flowing through so that the cable does not heat up, melt and start a fire. The reason we use fuses for the battery connection is that CB for the amps that the batteries give is just too expensive. Make sure it is a DC fuse with an Amp rating that is below what your battery cable can handle. (Normally this will be a 125A 56V fuse - they go for R500-R700 including a fuse holder)

Hi, Is this a SANS requirement or good practice? Be it fuse or DC CB. Thanks

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Thanks for the diagram. Because I am an absolute novice with this. 

On your other diagram the earth seems to be its own circuit connecting only to Eskom power source. what closes the loop? 

I really appreciate all the help. I will head off tomorrow to start getting the needed switches etc. 

Thanks

 

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1 hour ago, javadog said:

Thanks for the diagram. Because I am an absolute novice with this. 

On your other diagram the earth seems to be its own circuit connecting only to Eskom power source. what closes the loop? 

I really appreciate all the help. I will head off tomorrow to start getting the needed switches etc. 

Thanks

 

Hopefully the below should explain the earth circuit, please don't close the loop as per diagram 2

iE8Ls.jpg

9162157_f520.jpg

Edited by Bloubul7
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So, final piece of advice needed. 

Basically if I follow all the advice I will need the following

I have a 5KVA ,48 volt inverter and 4 x 12v 95AH batteries in series

I have it that the system can put out 23 Amps max (5000w/220v = 22.2)

DB Board: 

1 x earth leakage CB (40amp) 

1x normal CB (40amps) 

Out side DB board: 

1 x manual change over switch

Inverter

1 x 100 amp DC fuse for the batteries, or do I need one on both positive and negative?

And then all the wiring and trunking and stuff

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9 minutes ago, javadog said:

do I need one on both positive and negative?

One is fine for the battery. Most put it on the positive side, but it will be fine on the negative as well.
If you ever add solar panels, you should fuse each wire (positive and negative)

The rest of your items looks fine, but rather make that a 125A DC fuse and make sure it is a 56V and not 32V(32v are much cheaper)

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8 minutes ago, javadog said:

1 x 100 amp DC fuse for the batteries, or do I need one on both positive and negative?

ensure your battery cables are correctly rated for the potential current draw, then use fuses rated under the cable spec, so that the fuse(s) blow before the cable heats up and ignites...
I believe it's okay to use a single fuse, I have only 1 fuse on my positive battery cable but I'm about to install a 2 pole battery disconnect with fuses on both poles.
I've been looking at the Keto (manufactured by Jean Muller) disconnect but also the Mersen
Keto - https://www.google.com/search?client=firefox-b-d&q=Fuse-switch-disconnector+KETO

Mersen - https://www.google.com/search?client=firefox-b-d&q=Battery+Disconnect+Mersen

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Awesome thanks, I see that there are inline fuse holders and then the one you mentioned in the google search. 

apart from price difference and fuse type, any benefits to the Mersen  for example

Ideally the fuses to batteries can live in a box on  the wall but just curious as there is quite the price difference

image.png.ec5ba0d8bb7da3208c4d4b121b9c73d1.pngimage.png.da82a33ad639ceec407daf4387e00147.png

 

 

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The likes of the Mersen and Keto also act as a convenient disconnect (switch) which is useful when attaching the cables to the inverter. When I first did mine I had a good fuse but no switch/disconnect so when I was attaching the cables to the inverter I got a nice arc between the inverter contact point and the bolt with the cable lug as it got close enough, got quite a fright.
A battery disconnect is actually a good idea, partly for what I just mentioned but also if you need to disconnect the battery from the inverter for some reason.

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On 2020/08/13 at 10:17 AM, Bloubul7 said:

The neutral from your inverter output should go into a seperate neutral bar

Hi Bloubul7

That line is still confusing me. So I cannot bring the neutral from thee inverter  into here?

image.png.f8d7f019d10f1f67262f9ad3a9c6de34.png

 

 

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19 minutes ago, javadog said:

So I cannot bring the neutral from thee inverter  into here?

It's best to keep the neutral separate for everything on the output of the inverter.
Your change over switch will link both neutrals when you bypass the inverter. 

The earth is the same for them all.

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46 minutes ago, Louisvdw said:

It's best to keep the neutral separate for everything on the output of the inverter.

It is not only best, it is required!

1. Because if you don't, your earth leakae will trip repeatedly, and
2. Because SANS-10142-1 requires it.

There are a few rare cases where you can share the neutral, but none of that applies here 🙂

 

Edited by plonkster
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