I have Sol-Ark 5K inverter, 22 x 230W (CS6P-230P panels). Also I bought Midnight Solar MNPV6 DC Combiner Box with 4 15amp DC breakers. From what I understand this box is configured as a junction box for 4 strings. Each string would be wired individually to 15amp DC breaker and wired via 146' cable lenghts to my inverter. I have a 4" conduit installed with the string in the trench ready for the cable pull. My ground mount is in place and I'm getting ready to install my panels. When I bought my Sol-Ark I had my 22 panels already purchased and based on that I was told to configure my panels in 2 x 6 and 2 x 5 strings (I am planning to ad 2 more panels to make this 4 x 6 panels in the future). Initially I was told to buy tec #10 4C wire to connect my 4 strings to Sol-Ark inverter. I am having trouble understanding how this would work. That is one of the main reasons I did not buy the cable yet. I've discussed this with a friend (electrician) and we've agreed that running 4 separate cables might be the best option. 4 x 10\2, 4 x 12\2, 14\2 ??? I understand that I'm running hight voltage DC from the my array to Sol-Ark, but my Imp is only 7.78 amps per string. I would appreciate any coments.
Please help with the cable size for multiple strings
- Thread starter AndrewSad
- Start date
Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 20,688
Wires have an ampacity rating, which is reduced for elevated temperature or large number of current carrying conductors in a cable or conduit.
In addition, 14 awg, 12 awg, and 10 awg have a max allowed design current. 30A in the case of 10 awg.
Look up NEC ampacity table to see the figures.
For PV, multiply the string (or array if strings paralleled) current by 1.56. That gives the current to use when selecting wire with at least that much ampacity.
Look up resistance of wire, times Imp of the string or array, to determine voltage drop. Under 5% would be good, but it is OK to have more drop than that, would just be more loss during peak times.
With 7.78 amps per string (Imp or Isc?), 10 awg will be sufficient ampacity for 2 strings in parallel. 12 awg maybe not quite.
With separate wires for each string, 12 awg and 14 awg do have sufficient ampacity.
My strings are around 380 Vmp, 7A Imp, 100' or so. I use 12 awg separate for each string, and combiner box is at inverter.
You can combine pairs at array, no fuses needed if 2 strings into each MPPT. You can run extra wires or larger wires now, allowing for future expansion.
In addition, 14 awg, 12 awg, and 10 awg have a max allowed design current. 30A in the case of 10 awg.
Look up NEC ampacity table to see the figures.
For PV, multiply the string (or array if strings paralleled) current by 1.56. That gives the current to use when selecting wire with at least that much ampacity.
Look up resistance of wire, times Imp of the string or array, to determine voltage drop. Under 5% would be good, but it is OK to have more drop than that, would just be more loss during peak times.
With 7.78 amps per string (Imp or Isc?), 10 awg will be sufficient ampacity for 2 strings in parallel. 12 awg maybe not quite.
With separate wires for each string, 12 awg and 14 awg do have sufficient ampacity.
My strings are around 380 Vmp, 7A Imp, 100' or so. I use 12 awg separate for each string, and combiner box is at inverter.
You can combine pairs at array, no fuses needed if 2 strings into each MPPT. You can run extra wires or larger wires now, allowing for future expansion.
The exact design will depend on which sol-ark 5k model you have, the 5K-1P-N 120volt or the 5K-2P-N 120/240volt. Also we need to consider the record cold temperature at your location, we need to make sure the open circuit voltage of the strings will not exceed to the inverter rating.
You will need strings longer then 5 or 6 panels to reliability stay above the minimum 150volts of the sol-arks nominal operating range.
With the 5K-1P-N inverter I would do strings of 7s2p and 8s1p, going to 8s2p and 8s1p when you add the additional 2 panels. With the 5K-2P-N I would do 2 strings 10s1p with just 20 panels.
With no more then 2 strings in parallel no breakers or fuses are needed, the 2 strings can be combined with a MC4 branch connecting or joined in a junction box.
With one sting in parallel 12 AWG wire is sufficient, with 2 strings in parallel 10 AWG will be needed.
You will also want a ground wire to bond the frames of the solar panels and metal structure, this wire will run with the PV wires and connect to ground at the inverter. The wire can be 10 AWG when in conduit, but must be 6 AWG when exposed for physical protection.
You will need strings longer then 5 or 6 panels to reliability stay above the minimum 150volts of the sol-arks nominal operating range.
With the 5K-1P-N inverter I would do strings of 7s2p and 8s1p, going to 8s2p and 8s1p when you add the additional 2 panels. With the 5K-2P-N I would do 2 strings 10s1p with just 20 panels.
With no more then 2 strings in parallel no breakers or fuses are needed, the 2 strings can be combined with a MC4 branch connecting or joined in a junction box.
With one sting in parallel 12 AWG wire is sufficient, with 2 strings in parallel 10 AWG will be needed.
You will also want a ground wire to bond the frames of the solar panels and metal structure, this wire will run with the PV wires and connect to ground at the inverter. The wire can be 10 AWG when in conduit, but must be 6 AWG when exposed for physical protection.
I'm sorry if this is a duplicate, but I don't see my reply from 4 hrs ago. My Sol-Arc is 120/240V, model Sol-Ark-5K-48-ST. According to spec sheet I've found online: MPPT voltage range is 150-425V, max DC current per MPPT 10A/10A. It could get down to -40C at times, so I'd like to play it safe and compensate for that. I have looked at the specs of my panels Vmp 29.6V, Voc 36.8V, Imp 7.78amp and Isc 8.34amp, and I have looked at some formulas that tell me to multiply my Voc by 1.25 for max possible voltage. I might be getting 46V per panel. Is 4 strings with 2x6 and 2x5 panels be OK? As I mentioned I'd like to ad 2 more panels, so I might be able to reconfigure this to 3 strings of 8 panels each. Is it Ok to have 3 strings on this inverter? I would appreciate any suggestions on how to configure this in the best possible way.
Thank you! Thats exactly what I believe I should do after doing more research. I just realized last night tha I should be using Vmp for calculating minimum string voltage. Also my panels are 10 years old, so they might be producing less. I'll be connecting all the panels with a ground wire, and to the ground rod at the panels. I'm still not sure what cable should I use to connect my 3 strings to the inverter. I'm thinking 3 runs of 12\2 underground rated should be ok?
12 AWG is fine for individual strings, if you want to combine the 2 strings at the array you would need to use 10 AWG instead. 7x12 AWG, or 2x12 AWG and 3x10AWG, or 5x10AWG, would all be acceptable options. Even with a ground rod at the array code still requires are ground wire to be run with the PV circuits to bond all the grounds together.
I have talked to Sol-Ark support, and they have confirmed 10 Amp limit per MPPT on my inverter. So, my plan to run 3 strings of 8 panels each might not be best for my inverter. With 2 strings of 8 panels on first MPPT my input current would be ~16 Amps, so 6 Amps would be wasted. I don't know why they sold that model with an option to input 4 strings. The support guy could not answer that question. His suggestion was to run 2 strings with maximum panels per string. I have 22 panels, and according to https://www.sol-ark.com/solar-panel-sizing/SolarPanelSizing.html calculator I can use max 11 panels per string. I'm not buying those 2 extras panels and will just stick with 22 panels that I have. I am still debating the wire size. With 2 strings of 11 panels each Isc is 8.34 Amp per string, 146 feet (45m) distance. What are my least expensive options for a wire? I think I can use 2 runs of 12\2. How about using 12\3 cable and combining the negative at the array? I think I will still use Midnight Solar box that I already have. In that box there are 4 fuses for PV+ (since I was supposed to have 4 strings) and a common negative bar for PV-. Also, there is a grounding bar, that I was going to connect to my panels, grounding rod at the array, and ground wire to the inverter. With that box the negatives are getting combined at the array, so this looks like it might be an option. I would appreciate any suggestions.
Thank you for you replies. 14\2 I can find at Home Depot is only rated for up to 300V. They have 14\1 rated for up to 600V. Each of my strings might be running higher than 300V. Installing multiple 14\1 would be more time\effort, but this might be something I need to do. Also, for the ground wire between the array and the inverter should I use 14\1, 12\1 or heavier wire?
Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 20,688
14/2? Or 14/2 + ground? What kind of wire? Link?
We normally use PV wire exposed; that is water and UV resistance.
In conduit, I use THHN/THWN, which is rated to 600V, for PV home runs.
I've used UF, 12/2 + ground between PV panels, before MC connectors were a thing.
We normally use PV wire exposed; that is water and UV resistance.
In conduit, I use THHN/THWN, which is rated to 600V, for PV home runs.
I've used UF, 12/2 + ground between PV panels, before MC connectors were a thing.
My array is a ground mount. I have a 4" conduit already in the ground. I don't want to spend more than I have to for the cable. I have found this: https://www.homedepot.ca/product/southwire-14-1-rw90-300m-electrical-wire-white/1000400185. Also, they sell it by the meter. I need 45m per run.
Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 20,688
For conduit, individual wire is the way to go.
"RW90" Looks like you're in Canada, may have different names for wire.
that one says UV resistant, which is fine, though not needed within conduit. Also wet, needed for underground conduit.
In the US I use THWN, which is good for wet locations.
That one is white; I would get black if a single color, and use phasing tape to label. I've run enough I get spools of several colors. You may find that one full reel of black is cheaper.
Run a wire for ground as well, to bond PV panel frames to inverter.
"RW90" Looks like you're in Canada, may have different names for wire.
that one says UV resistant, which is fine, though not needed within conduit. Also wet, needed for underground conduit.
In the US I use THWN, which is good for wet locations.
That one is white; I would get black if a single color, and use phasing tape to label. I've run enough I get spools of several colors. You may find that one full reel of black is cheaper.
Run a wire for ground as well, to bond PV panel frames to inverter.
Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 20,688
That 60C is for the wet application, but 90C when dry?
Unlike AC circuits (where breaker trips for a short), size the ground wire of a PV array to carry continuous current. Because it won't get shut off.
For one PV string that is OK wired in 14 awg, same gauge for ground definitely fine.
If many PV strings, would have to consider whether multiple strings shorted could put current in it.
Unlike AC circuits (where breaker trips for a short), size the ground wire of a PV array to carry continuous current. Because it won't get shut off.
For one PV string that is OK wired in 14 awg, same gauge for ground definitely fine.
If many PV strings, would have to consider whether multiple strings shorted could put current in it.
