Wiring a combiner box for quicker installation on site.

Lumisol · May 2017

Quick question:
In a combiner box is it acceptable to use wire guages based on the run of that particular wire only or should you stay consistant with the wires being connected to it as well?

Example: I will be using 8awg mc 4 wires to run about 15 feet with 89 volts @17 amps (max amps is 17 but the breakers are 2 10 amps for 20 amps on the line before shutoff) I would like to build the combiner box prior to the installation since it is in a remote off grid location and want to wire the negative lug to an mc4 on the side.
Now according to the charts, I could use as small as 14 awg to connect the connector to the lug (about 6 inches of wire) and I was wanting to ise 12 awg single strand romex for this short internal connection since I have a roll of it sitting around. The lugs will accept anything from 14 to 6 awg.
Would it be fine to use the smaller gauge inside for the short run from the connector to the lug and then the 8 awg for the long run?

westbranch · May 2017

Short answer, use the largest wire that you can fit in the CB that matches the final number of PV runs you will use for the Combiner to CC. Larger is never a problem but if you undersize ( @ minimum) you may have to replace it in the future...but do not oversize your B's... stick to the makers recommendation of amp rating.
The lugs will accept anything from 14 to 6 awg.
The manufacturers use 10Ga stranded AFAIK for almost all PV to combiner for a reason (safety) and you want to go smaller to 14 and 12?
I have nothing in my combiners smaller than 10ga solid, after that I use 8 ga stranded..

hth

Lumisol · May 2017

No, I was going to use what I had, if I am going to buy new, I'll buy the 6 awg that will just fit.
Do your combiners have a larger or smaller than 89 volts at 17 amps total combined in them?

westbranch · May 2017

that is almost the same output in the 2 array combiner - combination I have right now. 2 x [ 4 x 140W panels, 17.9V, 7.85A ] but we are at 3000 ft and see more V in the cool air...
ADD: in BOLD

Lumisol · May 2017

I am at 6500 feet at the mountain place. I have 4 290 watt panels. It can get to 80 degrees there in the summer.

westbranch · May 2017

Which CC are you going to use?
What is the coldest winter temp you get?
What did the string calculator tell you for the max # in series for those panels?
I calculate about 3.26A Imp per panel if 89 V is correct = 13.04A for all 4 combined.

Lumisol · May 2017

westbranch said:

Which CC are you going to use?
What is the coldest winter temp you get?
What did the string calculator tell you for the max # in series for those panels?
I calculate about 3.26A Imp per panel if 89 V is correct = 13.04A for all 4 combined.

http://string-calculator.morningstarcorp.com/#manufacturer=424&module=10510&product=0&vmin=55.2&vmax=56.2&tmin=5&tmax=86&tminunits=f&tmaxunits=f&preview=1&stringnum=2&modulenum=2

Wiring a combiner box for quicker installation on site.

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