Hi everyone,

I recently purchased a Deye 8kW hybrid inverter (2025 model) and I have a question regarding the cable sizing used during the installation.

The Issue: The Deye manual specifies that a 10mm² twin and earth wire is required, paired with 50A breakers.

However, ive heard a few electricians say that 6mm² twin and earth (Nominal amp rating 51A) will work fine.

Planned Installation method:

• Cable Length: +/- 20m each way (Input and Output).

• Mounting: Running in the roof inside, each in their separate 20mm conduits, clamped to the roof beams.

• Breakers: 40A breakers at the combiner box, and 50A breakers in the main DB.

• Load: A CT clamp is installed, so the full household load is not passing through the inverter.

My Questions:

1. Given the 20m distance and conduit setup, do you agree that the 6mm² wire is sufficient?

2. I’ve heard suggestions to limit the max output to 7000W to prolong the lifespan of the inverter and reduce stress on the wiring. Is this recommended?

Any advice or insights would be greatly appreciated. Thanks!

Edited December 1, 2025Dec 1 by Potenza

Input or output to inverter? Input would typically be sized larger than output.

so the 6mm2 will work fine on the output but not the input to the inverter because it will pull current for both charging and supply of your house. That’s the max current that the cable will see.

So you MUST use the 10 on the input and you can use the 6 on the output. 6 is good for 40A if I’m not mistaken. Maybe a little more but it’s not enough to supply at full load and charge the battery simultaneously.

I don’t know if installing a current limiting breaker is enough for COC. That is use 6 on both input and output but have a 40/50A breaker to limit the current.

I personally would do it the right way. Use 10 and 6.

On the second point, yeah sure, less power means less heat so theoretically it could mean longer life for the semiconductors in the inverter. But then again, how often do people max their inverters? Rarely. So just use it normally in my opinion.

If the cable is sized right there is no such thing as stressing the cable. The only thing that fails over time is the insulation due to age or if you using the wrong class of insulation for the voltage. Otherwise don’t worry about the cable.

Edited December 2, 2025Dec 2 by Denns

Thanks Dennis

The 6mm wire is used for input and output

This is the inverter specs

Max AC input current 40A

Max AC output current 38.3A

Would you still suggest a 10mm for the input?

5 hours ago, Potenza said:

Thanks Dennis

The 6mm wire is used for input and output

This is the inverter specs

Max AC input current 40A

Max AC output current 38.3A

Would you still suggest a 10mm for the input?

I found this for the Deye 8kW (Seems to be similar to your inverter). Max passthrough current is 50A. Does not state what the max AC charging current is for your inverter. Is the 190A i see with the solar I am not sure, unfortunately. But looking at the SANS current handling ratings, 6mm2 is good for 49A max. The passthrough current of 50A already exceeds that. It still looks like you need the 10 on the input because the passthrough current of 50A does not include the charging portion of the batteries also. 10mm2 can handle 67A which is about 15kW. So it leaves you with 7/8kW to charge the batteries while simultaneously supplying full load.

11 minutes ago, Denns said:

I found this for the Deye 8kW (Seems to be similar to your inverter). Max passthrough current is 50A. Does not state what the max AC charging current is for your inverter. Is the 190A i see with the solar I am not sure, unfortunately. But looking at the SANS current handling ratings, 6mm2 is good for 49A max. The passthrough current of 50A already exceeds that. It still looks like you need the 10 on the input because the passthrough current of 50A does not include the charging portion of the batteries also. 10mm2 can handle 67A which is about 15kW. So it leaves you with 7/8kW to charge the batteries while simultaneously supplying full load.

Also look at the bright side of using 10mm2, You could potentially install a bigger inverter in the future. Would be limited by the 6mm2 on the output though.

16 hours ago, Potenza said:

However, ive heard a few electricians say that 6mm² twin and earth (Nominal amp rating 51A) will work fine.

16 hours ago, Potenza said:

1. Cable Length: +/- 20m each way (Input and Output).

2. Mounting: Running in the roof inside, each in their separate 20mm conduits, clamped to the roof beams.

The current rating (ampacity) of a 6mm² Surfix cable in a conduit installation is 36 Amps under standard South African installation conditions (Method 3 in SANS 10142-1). This value is the standard current rating, which is then subject to further derating factors based on specific installation conditions. While the 36A rating is for the conduit method, any deviation from the standard installation method (e.g., longer runs in thermal insulation) may require additional derating. 

The Deye 8kw has a passtrough rating of 50A that means it can pass 50A from input to output so the cable and breaker must be rated for the passtrough spesification and the breaker rated to protect the cable. The roof space can during summer exceed 30°C further derating the cable integrity. Stick to the OEM cable spesification and calculate the voltdrop and you would see using 10mm² cable for input and output would be the safe option. Safety is more important than cost.

Also ensure when purchasing Surfix Norsk or any electrical cable that it has the SANS or SABS marking on it. There is plenty of cables out their that consist of alloy conductors that increases the resistance/ km considerably. There is a non profit organization SAFEHOUSESA that explicitly warns about sub standard cables.

https://safehousesa.co.za/wp-content/uploads/2020/03/Safehouse_Combined-Guides-1.pdf

Edited December 2, 2025Dec 2 by TaliaB

Here is a good example of passtrough on a 5kw Sunsynk inverter by using all the power sources available the power on the ups side(output) is elevated far above 5000w.

Edited December 2, 2025Dec 2 by TaliaB

11 minutes ago, TaliaB said:

The current rating (ampacity) of a 6mm² Surfix cable in a conduit installation is 36 Amps under standard South African installation conditions (Method 3 in SANS 10142-1). This value is the standard current rating, which is then subject to further derating factors based on specific installation conditions. While the 36A rating is for the conduit method, any deviation from the standard installation method (e.g., longer runs in thermal insulation) may require additional derating. 

The Deye 8kw has a passtrough rating of 50A that means it can pass 50A from input to output so the cable and breaker must be rated for the passtrough spesification and the breaker rated to protect the cable. The roof space can during summer exceed 30°C further derating the cable integrity. Stick to the OEM cable spesification and calculate the voltdrop and you would see using 10mm² cable for input and output would be the safe option. Safety is more important than cost.

Also ensure when purchasing Surfix Norsk or any electrical cable that it has the SANS or SABS marking on it. There is plenty of cables out their that consist of alloy conductors that increases the resistance/ km considerably. There is a non profit organization SAFEHOUSESA that explicitly warns about sub standard cables.

https://safehousesa.co.za/wp-content/uploads/2020/03/Safehouse_Combined-Guides-1.pdf

Ah yes, I used the table for clipped direct. Not in conduit. Makes quite a difference for heat dissipation. Mine is in a conduit clipped to the wall, not inside, so my cable ratings are a little higher.

Edited December 2, 2025Dec 2 by Denns

Thanks for all of the advice,

I will rather then pay the extra bucks and get the 10mm cable then

Question 1

The passthrough rating, does that mean that the whole house load, passes through the inverter?

Question 2

This is the installation components that I found of a website of a reputable solar/ aircon company

They are offering the exact same inverter like mine, also 8KW

They are using 6mm cable 15m lengths, paired with 50A and 40A breakers in the combiner box

And they are issueing a COC for the installation is this legal?

45 minutes ago, Potenza said:

And they are issueing a COC for the installation is this legal?

No 6mm² cable needs to be paired with a 30A or 32A Mcb not 50A. Every company is cutting cost use 10mm2 input and 10mm2 output with 50A mcb. Victron spesifications for a MultiPlus-II 8000va stipulates 16mm² input and output cables. Don't take shortcuts to save a few bucks not worth it.9

Thanks Talia

Scary how some companies install undersized cabling

Especially if the client does not know anything about solar

Im going 10mm on my setup

8 hours ago, TaliaB said:

No 6mm² cable needs to be paired with a 30A or 32A Mcb not 50A.

Because it's a fire risk. Circuit breakers don't protect us, they protect the cable. If the cable is rated at 30A and you have a 25A breaker, the breaker will trip before the cable can overheat.

If the same cable is paired with a 40A breaker, then the cable can start heating up before the breaker trips (if it does).

8 hours ago, Potenza said:

Thanks Talia

Scary how some companies install undersized cabling

Especially if the client does not know anything about solar

Im going 10mm on my setup

Great!!

On 12/2/2025 at 3:48 PM, TaliaB said:

10mm² cable for input and output would be the safe option. Safety is more important than cost.

I am using 6 mm for 5000 W input and the cable is 4 floors length = 12 meter , do you think is it ok ?

1 hour ago, esmail-kassir said:

I am using 6 mm for 5000 W input and the cable is 4 floors length = 12 meter , do you think is it ok ?

You need to say what panels and how many as well as 1 or 2 strings in parallel to get the right answer.

At the face of it using 450+W panels in up to 2 strings the 6mm should be OK if the current is less than 30-32A.

On 12/2/2025 at 3:48 PM, TaliaB said:

10mm² cable for input and output would be the safe option. Safety is more important than cost.

I am using 6 mm for 5000 W input and the cable is 4 floors length = 12 meter , do you think is it ok ?

19 minutes ago, Scorp007 said:

You need to say what panels and how many as well as 1 or 2 strings in parallel to get the right answer.

At the face of it using 450+W panels in up to 2 strings the 6mm should be OK if the current is less than 30-32A.

we are talking about Grid AC input here