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xpim asked

Wire type and ferrules

I'm working on buying and installing a PV system and I'm running into some questions here and there.

I'll have 3 strings of 4 panels running at About 200V and 33A

I'll have 10mm wire coming out of the combiner box running into a MPPT 250/100 charge controller.


I'll have to run 15/20meter of wire from the combiner box to the solar charger and I'm having trouble finding a decent price for a really fine strand 10mm wire. I can find "regular" flexible copper wire with strands of about 0.5mm (maybe less but I rather have the worst picture...).


I've read the solar charge controller and wire information here and there and it seems that I need finer strands. I can also add ferrules since I even have a decent crimper for them but I'm afraid it's not the best choice.


How bad is it to use *not so fine* strand wire on the input?


On the charge controller output I'll be able to use the correct fone strand wire since it will be only about 1 meter at most.


Virtually every single other part on the system will use crimped wire terminals and they don't worry me as much.

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7 Answers
atebee avatar image
atebee answered ·

6mm solar PV has a current rating of about 70A depending on situation (free air etc). I would use this personally as it is double insulated. Also has fine strands.

I believe ferrules aren't recommend for terminations on the MPPT.

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nickdb answered ·

Do not use ferrules on PV chargers.

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jetlag avatar image
jetlag answered ·

I have a similar situation running a ~4kWp array on only 80V but up to 50A from a combiner box to the MPPT with 16mm² "standard" solar cable. This is outdoor rated and double isolated. I used ferrules in the combiner box, but on the MPPT, there are clamps that don't required ferrules. So there you can go directly with the blank wire into the MPPT.

You most probably won't find a better "fine" strand calbe for the solar connection. On the battery side, where the current is much higher then, you should use the best cable you can get.

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xpim avatar image
xpim answered ·

Relevant wire specs: Copper wire bare, finely stranded acc. to DIN VDE 0295 Class 5 / IEC 60228 Class 5

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xpim avatar image
xpim answered ·

I'm weary about dumping much more than 30A on 6mm wire... it would simplify a lot after the combiner box...

I always worry on losses/voltage drop and heat.

its going to be around 34A dead short after the combiner box... maybe I'm overdoing it?

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atebee avatar image atebee commented ·

You are overthinking it. 6mm has 70A capacity at 60C ambient temperature. So 34A in normal conditions is well within it's limits.

Voltage drop is like 2% at 34A which is nothing and you spend very little time operating at maximum current.


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xpim avatar image xpim commented ·

could add up do 20W on wire losses... its kinda low on a 5700W array I guess

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xpim avatar image
xpim answered ·

I have quite some time to overthink... the batteries are going to take another 30/40 days to arrive. I'm ordering other parts and preparing. when they arrive I have to check them and probably do a couple of full cycles... it seems PV wires are sorted out. thank you!

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xpim avatar image
xpim answered ·

on the output of the charger I'll use really decent fine strand copper wire the thickest I can get on the mppt controller (35mm according to the manual) on that side is a small lenght. its not hard to go for a decent cable.


same on the inverter and batteries. I'm going thicker with decent cables. most connections (virtually all) there will have crimped terminals.

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