Negative wire sizing as it relates to the Electrodecus system.

[Justin]

Does the negative wire from were all the PV modules combine into one wire need to be 1.25 or 1.56 the panels ISC. I have 3 DSSR50 with (3x 450W/13.82 ISC and one 330/10.33 ISC) as well as one DSSR20 with a single 450W/13.82 ISC panel for a total ISC of 169.19 amps.

Can I use a 4/0 wire (169.19 x 1.25 = 211.49) or do I need 262 MCM (169.19 × 1.56 = 263.94). Each DSSR50 has a 63 amp breaker and the DSSR20 has a 20 amp breaker. So based on the circuit protection after the charge controllers I should be able to use 4/0 on the positive (63 + 63 + 63 + 20 = 209 amps). I also have a 225 amp fuse on the 4/0 cable before the 300 amp shunt.

The negatives combine outside the cabin. I combine the negatives there so I could use 1/2 a surge protector for the negative (had to combine the individual arrays there). There are 7 positive array cables. Each surge protector can do two wires so four surge protectors total. The positive array cables combined into one cable downstream of the DSSR5s/20 of course. The location for that is inside the cabin closer to the battery.

What size do I make the negative cable? I struggled to find the answer online. Most situations have the negative going to a mppt after the combiner box. My positive and negative wires are combined in two different places. Will this be a problem?

[Dacian Todea (electrodacus)]

1.25 x the Isc is what you can expect as peak and it will not be for long seconds or at most a few minutes. It will drop fast to 1 or max 1.1x Isc

So if the insulation on that wire is at least 75C probably is 90C then 4/0 will have no problem with this current and fusing.

[Justin]

Should the negative have a fuse or breaker. I'm assuming it shouldn't because it's the grounded conductor?

[Dacian Todea (electrodacus)]

You have fuses and breakers on the positive side so you do not need any fusing on the negative.