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Cable size from DB to Inverter


kobus joubert

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51 minutes ago, kobus joubert said:

Will 2.5 flat twin +earth be ok or should I go at least 4mm flat 2+earth?

What is the max the inverter can produce? That is the cable size that you should install.

My case electricians installed a 10mm2 cable. Subsequently installation changed, now I have the 10mm2 cable spare. Ai tog.

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42 minutes ago, The Terrible Triplett said:

What is the max the inverter can produce? That is the cable size that you should install.

It's a bit more complex than that. It depends also on what kind of inverter is installed.

First scenario, arguing for thinner wire: In my own setup I have a transfer switch capable of passing 50A, so if I want to use the full capacity, I should install cable that can handle 50A. I don't have a need for the whole 50A, so I have instead opted for 4mm Surfix (which limits me to 32A), and installed breakers on either side to limit me to 32A.

Second scenario, arguing for thicker wire in some cases: Even though my 3KVA inverter is capable of only around 14A on its own, I have to consider the max current that it needs to pass in bypass mode (which in my case is 50A, or however much I want to use).

Third scenario, also arguing for thicker cable in some cases: I Have a Victron inverter that can do PowerAssist, so that the power in is not necessarily equal to the power out. Even if the input of the inverter has a breaker limiting it to 25A, I still need a suitable breaker (or a thicker cable) on the output side if I want to use this feature. So in some scenarios the cable on the output side and the corresponding breaker might be larger than the one on the input side.

In the end the question pretty much comes down to: How much power is this cable expected to carry. You can size it smaller than the inverter (if you don't expect to use the full capacity), and you must size it larger than the inverter power if there is a bypass switch and any potential that more power might pass that way, but overall, the important part is that whatever decision you make, you add breakers to make it safe.

1 hour ago, kobus joubert said:

Will 2.5 flat twin +earth be ok or should I go at least 4mm flat 2+earth?

2.5 is too thin, I believe it is only good up to around 20A. At least 4mm is required. Also note that not all Surfix is created equal, I recently noted that some brands are rated for 32A and others for only 28A.

There is also the matter of how long the cable will be. SANS specifies maximum voltage drops and you might have to go thicker if the cable is too long.

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The distance is about 8 meters between DB and Inverter.

Like I said, we only have a 30 Amp connection from the Municipality.

We do not trip their 30A breaker supplying the house when we use their AC in the house.

Therefore we will not exceed 30 A through the Inverter AC connection.... or am I missing something 

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5 minutes ago, kobus joubert said:

The distance is about 8 meters between DB and Inverter.

Like I said, we only have a 30 Amp connection from the Municipality. 

Right, and as I recall you don't have a hybrid inverter. You still have to use at least 4mm. I'm not an electrician, but if I plug those numbers into a random drop calculator, it says you're below 1% drop so you will probably be fine.

@Jaws seems to be the man to ask about these things though 🙂

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7 minutes ago, kobus joubert said:

Is the Axpert not a Hybrid Inverter ?

Not by the correct definition of the term, no. Although I've had in depth arguments about this with people who insisted that it was (based on a different definition of Hybrid).

A hybrid inverter is like a grid-tied inverter, but it can also do battery storage and work off-grid if there is a failure. It can "mix" power so to speak, so when the battery is low or there isn't enough PV, it would take the difference from the grid. Examples are the Victron Multiplus, the Goodwe inverters, Voltronic InfiniSolar range, Imeon inverters, and so on. The Axpert can't do that.

Some people define Hybrid as "can also charge the batteries and power the loads from the grid". Others interpret Hybrid as "has a solar charger and an inverter in one unit". Hence the arguments.

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Depending on how easy it would be to replace in future, for whatever reason, I would go one size bigger than the minimal need - purely  cause if you need it, it's there already. i.e. if you say only need 32A now, what will you do when you suddenly need say 50A? Life happens. I got two more kids since I installed my initial system and consequently had to upgrade in order to cater for our changed lifestyle.

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  • 2 weeks later...

I have a 20m run from inverter to DB, I only have a 3Kva 2.4 kw inverter but I installed 6mm cable. My plan is to install 2x 5kva inverters later. The wife want to keep the oven 

During my research the 6mm can only carry 42A when in conduit with a voltage drop op 7.9mv/A/M. in free air it can do 63A.

10000w/220= 45A 

for 5000/220=21A the 4mm cable will be fine. If you do not plan to upgrade the system. 

 

 

image.thumb.png.d070f847b9035e70402444213ac68e3c.png

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  • 4 years later...
  • 9 months later...

Good day I aslo have a 3.5KW 24V inverter system. AC input and output is connected on 2.5mm Surfex cable. During loadshedding max watts I am using is 500W. Don't use the maximum watts of the inverter. Sometimes you forgot about loadshedding then you use the kettle where you use 2.2KW for a few minutes. Have read most of the commons. What is the best size for AC input and output for the inverter. I know it depend on for size of inverter and load you want draw from the inverter.

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So best is to look at the SANS current carrying capacity of different sized cable in different installations and then use the appropriate one based on the size of the inverter(s) you have installed.

 

Below is multicore & single core.

 

CableWireCurrentratingsSANS(Multicore).png.c13b3ef51d37d3ac4a7017a62d110bfc.png

CableWireCurrentratingsSANS.thumb.png.ee9b967b77c3cd69fe46aaa64bb439eb.png

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