I have recently had two stings of 3 X 330 watt PV's installed, and I have been alerted that the feed cables to the inverter from the DB board may be too light?

Please refer to the image below. The photo shows two 4mm cables from each string of 3 panels coming into the DB (4 cables 4mm) and 2 x 4 mm cables leaving the box to feed the inverter.

I have 6 panels at present but the db has been wired for 18 panels, and I am concerned that the inverter-feed cables from the box are too light, not only for now but certainly  for when we add more panels?

Comments and advice would be much appreciated

Edited November 12, 20195 yr by Bushtracker
notify me of response

the output will definitely be too light later when you add much more. what is worse is the colour coding 😛 

Why did you opt for 2 strings of 3 panels that are connected in parallel in the DB?

Why not 1 string of 6 panels??

4 minutes ago, Richard Mackay said:

Why did you opt for 2 strings of 3 panels that are connected in parallel in the DB?

Why not 1 string of 6 panels??

maximum input voltage?

Maybe.

Bushtracker needs to let us know what the max voltage is for the inverter.

But I would connect as many panels in series that the inverter could handle.

1 hour ago, Richard Mackay said:

Maybe.

Bushtracker needs to let us know what the max voltage is for the inverter.

But I would connect as many panels in series that the inverter could handle.

I'm betting it is 145

14 hours ago, Bushtracker said:

not only for now but certainly  for when we add more panels?

What is the distance from this Combiner to the Inverter?

 

EDIT: You are aware that your lightning arrestors is not connected and offers no protection currently?

Its a pity that the installer plans to run all positive wires through one isolator/breaker and all the negative wires through the other. Effectively you will never be able to isolate one string at a time. Once you switch off either of the 2 breakers/isolators, all the strings are isolated. 

The fuses in this setup will not have any effect even after adding 6 strings as 3 strings will be combined on each of the 4 incoming connections of the 2 PV breakers. 

This Combiner  is designed for 6 strings in and 3 strings out. I would wire this completely different. 

1. Remove the bride pieces above the Fuse holders, 
2. Take each string to its own + and - fuse holder.
3. Combine the fuses at the bottom
4. then take the combined feed through on 63 A Breaker/isolator to your inverter. 
5. Use one surge arrestor for the + wires after combining them and the other surge arrestor for the - wire after combining them . 

That way , you can isolate each string individually, your have fuse protection in a multi string setup, Something you dont have now as the combining will happen before the fuses, and currently the current of the string is divided over 3 fuses. And lastly, you will have one Isolation point to isolate all the strings at once when you need to work  on the inverter 

I have spotted the same that Jaco have spotted. And how do you know what wire from the pannels is + and -. 

Thank you all for your advice and comments!

13 hours ago, Richard Mackay said:

Why did you opt for 2 strings of 3 panels that are connected in parallel in the DB?

Why not 1 string of 6 panels??

I can't answer this, neither did I query it with the installer. Will have to go back to him

 

12 hours ago, Richard Mackay said:

Maybe.

Bushtracker needs to let us know what the max voltage is for the inverter.

But I would connect as many panels in series that the inverter could handle.

The max voltage for the inverter is 145 v (see photo below)

1 hour ago, Jaco de Jongh said:

What is the distance from this Combiner to the Inverter?

 

EDIT: You are aware that your lightning arrestors is not connected and offers no protection currently?

Its a pity that the installer plans to run all positive wires through one isolator/breaker and all the negative wires through the other. Effectively you will never be able to isolate one string at a time. Once you switch off either of the 2 breakers/isolators, all the strings are isolated. 

The fuses in this setup will not have any effect even after adding 6 strings as 3 strings will be combined on each of the 4 incoming connections of the 2 PV breakers. 

This Combiner  is designed for 6 strings in and 3 strings out. I would wire this completely different. 

1. Remove the bride pieces above the Fuse holders, 
2. Take each string to its own + and - fuse holder.
3. Combine the fuses at the bottom
4. then take the combined feed through on 63 A Breaker/isolator to your inverter. 
5. Use one surge arrestor for the + wires after combining them and the other surge arrestor for the - wire after combining them

That way , you can isolate each string individually, your have fuse protection in a multi string setup, Something you dont have now as the combining will happen before the fuses, and currently the current of the string is divided over 3 fuses. And lastly, you will have one Isolation point to isolate all the strings at once when you need to work  on the inverter 

 

The distance from the combiner to the inverter is 1metre.

 

Your inputs are most appreciated I will meet with the installer and endeavor to have the wiring rectified soonest

15 hours ago, Dex_ said:

the output will definitely be too light later when you add much more. what is worse is the colour coding 😛 

Thank you Dex I have taken note. So what would you recommend as a suitable (correct size) of cable for the output. I am assuming that the existing cable size for the inputs are OK ?

 

 

 

 

 

4 minutes ago, Bushtracker said:

The distance from the combiner to the inverter is 1metre.

Although 4 mm and 6 mm shows acceptable volt drop values over 1 meter, I would have used at least 10mm wire between my combiner and inverter. (Calculated on 18 x 330 watt panels)

34 minutes ago, Bushtracker said:

14 hours ago, Richard Mackay said:

Why did you opt for 2 strings of 3 panels that are connected in parallel in the DB?

Why not 1 string of 6 panels??

I can't answer this, neither did I query it with the installer. Will have to go back to him

No need, you can only do three in series with a 145Volt MPPT. 

3 hours ago, Jaco de Jongh said:

You are aware that your lightning arrestors is not connected and offers no protection currently?

yeah... and I would use green and yellow wiring from the ground terminal on the surge arrestor. Seriously, this is inside a DB board where there is no sunlight that degrades wiring, and the green/yellow panel wire is cheaper than the PV cable used here. That is in addition to losing the colour coding first-glance information that would come with such wiring.

Also don't understand why the fuses are bus-barred at the top. I can understand that it is a three string combined of which not all are used right now, but then kill the busbars as you indicated.

Finally, those look like Gewiss breakers. They are rated 50V per contact (assuming they are the same ones I have), so if you break both the positive and negative (as here) you're rated to 100V only. Find the data sheets and make sure they are rated high enough.

6 minutes ago, plonkster said:

Finally, those look like Gewiss breakers.

I did not even see this. What i did see and at first did not want to comment on, is the L/N sign on the Surge arrestor. I would have expected to see  a + & - .  I thing they have used AC rated surge arrestors in a DC combiner box. If i look at the component election, I would also expect them to have used AC fuses instead of DC fuses.

@Bushtracker  , that is something you need to check out. If these components are AC rated instead of DC rated, you've basically have no protection.