# DC CONDUCTOR AMPACITY CALCULATIONS HELP

Registered Users Posts: 17 ✭✭
I used an online company to do my solar site plan packet for my local Building & Safety Department. They have done some calculations that look a little off to me. If anyone could help out with correct values, I would really appreciate it, the N.E.C. Tables 310 series are just confusing me. The image is from combiner boxes at array to inverters. It has (4) current carrying conductors @ 4AWG. ISC=9.11. There are 8 strings of 3 modules coming from each combiner box. I don't believe it has a bearing on the calculations, but I'll be using Schedule 40 1-1/4" PVC conduit. If more details are needed, let me know.

• Registered Users Posts: 4,496 ✭✭✭✭✭
"There are 8 strings of 3 modules coming from each combiner box".

To clarify - you have a total of 16 strings (16x3=48 panel)? These go two 2 combiner boxes, 8 strings per box. From each box they propose a pair of 4ga wires to charge controller/inverter(s).

The required ampacity line appears to be 4 strings per box, not 8 (9.11x1.25x1.25=56.94), which it seems to me would be for 24 panels, 8 strings total split 4 per box. How many panels are you getting?

As well as meeting code, voltage drop may be a factor if going any distance from array combiners to controller.
Off-grid.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
• Registered Users Posts: 137 ✭✭
ISC=9.11. There are 8 strings of 3 modules coming from each combiner box.
If there are 8 strings with an Isc of 9.11 being combined, shouldn't the required ampacity (after calculations) be greater than 8*9.11=72.88 A?
• Registered Users Posts: 17 ✭✭
Estragon,
my system will have 48 panels.
2-MNPV12 combiner boxes
2-GS8048A inverters
4-flexmax FM80 charge controllers
• Solar Expert Posts: 9,511 ✭✭✭✭✭
Putting panels in series and using a pair of 600V 80A charge controllers could simplify things a lot.   And save on wire cost.
Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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• Registered Users Posts: 4,496 ✭✭✭✭✭
In that case it appears the wiring will be inadequate, so heavier and/or more wires, and/or more conduit to reduce fill factor derating, and/or consider high voltage controllers.
Off-grid.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter