shared neutral from combiner box?

[callmeburton]

Not sure if this is a "thing" or not ...
1 combiner box with 2 outputs to two separate charge controllers and 1 shared neutral ... like a 2-2-4 AL URD cable to blocks torqued to spec with copper going the rest of the way.

If someone did this would you calculate voltage drop using the 4awg wire with both loads?

I have only ever seen non-shared neutral wiring from combiner boxes and was wondering, since they tie to each other in the panels, if this was possible and if so what it would mean for voltage drop since you would have less cross sectional wire on the neutral side of the circuit.

 

[Zil]

Interesting question.
I would calculate the voltage drop in each 'leg' separate. Using the 2 combined amperes for the shared negative. then add the three together for the total estimated voltage drop. I hope the aluminum is very short.

 

[callmeburton]

Interesting question.
I would calculate the voltage drop in each 'leg' separate. Using the 2 combined amperes for the shared negative. then add the three together for the total estimated voltage drop.

would the estimate be all 3 combined?! the two 2awg wires would be carrying the current from PV to individual MPPT's so maybe add the 4awg (which has combined) to individual 2awg results for voltage drop for one MPPT charge controller ?

I think the voltage drop for 300ft, as a single set of conductors, with 2awg is 5.76 with my system on the hottest day of the year using ISC amperage levels ...
on the 4awg wire it would be 18.32 ... those combined is 24.07 ... 4awg as the single set the voltage drop would be 9.16.

So the answer might be one MPPT charge controller could see a 5.76, 9.16, or 24.07 drop ... or as you said all three combined which would be 29.83.

Worst case go with 4/0-4/0-2/0 URD ... even with the worst case with "all combined" it would only be 12.95

But to me it still seems like you would calculate this as a single set using the smallest gauge wire (2awg above) to get the total drop.

I hope the aluminum is very short.

These are large gauge wires so not too concerned with it being short. URD AL cable isn't too expensive when compared to copper right now.

 

[WYtreasure]

Welcome to the party Burton.

I look forward to seeing the answers to your questions

 

[callmeburton]

Welcome to the party Burton.

Thank you. We are going to be setting up our system this year and it should be interesting for sure. There are some other posts I plan to make soon which haven't been covered yet so I hope to contribute to the community where I can.