(12) Panel 6S2P Design Questions: MC4 Splitters x Combiner Box? Wires or Cables? Conduits or not?

[Old_Skewler]

Here is the (12) panel design I am working with, two parallel strings of (6) panels in series each. Panels to be Canadian Solar HiKu6 400W @ 108 cells connected to a Victron 250/70 MPPT & 48V battery bank with 15 kWh capacity.



I have a few lingering questions that I could use some help of feedback with:

1. MC4 cable\ing and MC4 splitters seems to be cheaper than running (2) sets of cables down the house to a combiner box but I believe the combiner box is worth the extra price in terms of safety (fuses) and functionality (disconnects). Is this correct? Or is it overkill for this small installation? I ask this because most of the combiner boxes I've seen seem to be for more than 4 strings... And If I were to use splitters on the roof I would have to only run (1) set of cables down the roof instead of (2) sets.

2. Assuming I go with the combiner box on the side of the house, how should I run the (2) sets of MC4 cables along the roof/side of the house? I suspect the answer is in a conduit. If so, should I be able to run the (4) cables inside one conduit on the roof? Or should I expect to run two conduits on the roof?

Thanks in advance!

 

[timselectric]

I wouldn't use a combiner box. It's a waste of money in my opinion. I would recommend a disconnect near the SCC.
Cables should be in conduit. If more than one circuit. They can be in the same conduit.

 

[Zwy]

Here is the (12) panel design I am working with, two parallel strings of (6) panels in series each. Panels to be Canadian Solar HiKu6 400W @ 108 cells connected to a Victron 250/70 MPPT & 48V battery bank with 15 kWh capacity.

It works better if you put up a link to the datasheet.

View attachment 152091
I have a few lingering questions that I could use some help of feedback with:

1. MC4 cable\ing and MC4 splitters seems to be cheaper than running (2) sets of cables down the house to a combiner box but I believe the combiner box is worth the extra price in terms of safety (fuses) and functionality (disconnects). Is this correct? Or is it overkill for this small installation? I ask this because most of the combiner boxes I've seen seem to be for more than 4 strings... And If I were to use splitters on the roof I would have to only run (1) set of cables down the roof instead of (2) sets.

2 parallel strings do not need a combiner box.

2. Assuming I go with the combiner box on the side of the house, how should I run the (2) sets of MC4 cables along the roof/side of the house? I suspect the answer is in a conduit. If so, should I be able to run the (4) cables inside one conduit on the roof? Or should I expect to run two conduits on the roof?

Thanks in advance!

You can run 2 sets of cables if desired inside one conduit. This allows smaller wire size per cable set and less power loss. Each string would only be 12.99A instead of 26A.

 

[Old_Skewler]

I wouldn't use a combiner box. It's a waste of money in my opinion. I would recommend a disconnect near the SCC.

Understood. If I don't go with the combiner box then I should be able to use MC4 splitters at the roof level, correct?
Then run (1) set of MC4 cables down the house and 25 feet over to the battery shed. At this point I would add a PV DC disconnect inside the shed. Would this be acceptable?

Lastly, if I don't go with the combiner box, I suspect I would need to add some sort of safety device (inline fuses?) by the panels, on the roof? Could you share which components/device I should consider for this installation if I remove the combiner box from the system?

Cables should be in conduit. If more than one circuit. They can be in the same conduit.

Cool, got it.

 

[timselectric]

Understood. If I don't go with the combiner box then I should be able to use MC4 splitters at the roof level, correct?

Yes
Try to put them where you can easily access them later. In case you need to troubleshoot an issue.

Then run (1) set of MC4 cables down the house and 25 feet over to the battery shed. At this point I would add a PV DC disconnect inside the shed. Would this be acceptable?

Yes

Lastly, if I don't go with the combiner box, I suspect I would need to add some sort of safety device (inline fuses?) by the panels, on the roof? Could you share which components/device I should consider for this installation if I remove the combiner box from the system?

I used a DC breaker for the disconnect.
Two birds with one stone.
But over current protection isn't required for 2 or less strings in parallel.

 

[Old_Skewler]

It works better if you put up a link to the datasheet.

Fair enough!

2 parallel strings do not need a combiner box.

Great! It feels like it simplifies the installation.

You can run 2 sets of cables if desired inside one conduit. This allows smaller wire size per cable set and less power loss.

Understood! Okay, what do you think makes more sense in my application: I have approximately 80 feet run from the panels at the roof to the battery shed, where the MPPT goes. Where would you place the parallel-string Y-splitter: at the roof near the panels (hence1 set of wires left to run 80 feet to shed) OR place the Y-splitter inside the shed, requiring 2 sets of wires to run 80 feet to the shed?

 

[Old_Skewler]

Yes
Try to put them where you can easily access them later. In case you need to troubleshoot an issue.

Yes

I used a DC breaker for the disconnect.
Two birds with one stone.
But over current protection isn't required for 2 or less strings in parallel.

Amazing! Just incredible how this little thing called internet actually works sometimes! It has taken me at least two weeks just to figure out where I was stuck and how /what to ask for help...

Thanks again!

 

[Zwy]

Fair enough!


Great! It feels like it simplifies the installation.


Understood! Okay, what do you think makes more sense in my application: I have approximately 80 feet run from the panels at the roof to the battery shed, where the MPPT goes. Where would you place the parallel-string Y-splitter: at the roof near the panels (hence1 set of wires left to run 80 feet to shed) OR place the Y-splitter inside the shed, requiring 2 sets of wires to run 80 feet to the shed?

I'd look at wire price and availability first. 10AWG can handle the 26A, 14AWG can handle the 12.99A.