Solar cables size to MPPT . Combiner ?

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Herve RV Nizard asked Aug 3, '19

Solar cables size to MPPT . Combiner ?

9 x 270 w solar panels in 3S 3p

Max 42v - 9a

MPPT 150/100

I generally use 10awg (2,5mm) solar panel cables . This system has 9 panels in 3 series of 3.

If i wire and use Y MC4 (without a combiner box), I could have only 1 pair of solar panels cables from the roof to the MPPT which is 90 feet away.

This pair will roughly support 120 v and 27a at max. I am a bit worried with the size of the cables .

Would you think 10awg is large enough for this ? Or would you consider preferably:

1/ a combiner box close to the roof and then a larger cable to the MPPT ? May be 6 mm.

2/ or leave 3 pairs so each will be 120v/9a which is more acceptable for this size of cable ?

Thanks for your input.

MPPT Controllers wiring system design

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Answer 1 · 2019-08-03T17:54:19Z

wkirby answered · Aug 03, 2019 at 05:54 PM

I'd prefer option number 1.
More than two strings in parallel warrants a fuse for each string, hence a combiner box.
If a fault develops in one string, then the other two strings could deliver 18A into the faulty string and potentially set them of fire since they are only supposed to carry 9A each string.

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Answer 2 · 2019-08-03T19:19:22Z

Herve RV Nizard answered · Aug 03, 2019 at 07:19 PM

@wkirby . thanks. What size cable would you recommend for the 90 ft from the combiner to the Mppt ?

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Answer 3 · 2020-05-20T10:56:41Z

Simon Phillips answered · May 20, 2020 at 10:56 AM

I am installing a 6 Panel ( string ) set up to a combiner box in parallel on a boat ( shading issues dictates this ) but similar concept my max run is 43 feet , I am considering using 8 Awg for this long run due to loses but 10Awg maybe ok , I personally would not want to use 10Awg for 90feet ( 30m ) but then I have only 30volts to play with at 120v a volt or two lose extra probably is not critical but depends on your application and whether it is money making or just serving your needs

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