# Maximum mc4 cable run

DarkstormNH
Registered Users Posts:

**34**✭✭
is it safe to run 4 run of mc4 10 awg the lowest I can find to make a 120 feet run to combiner box?

voltage for two 325 watts panel in series would be 94 volts, please advise

voltage for two 325 watts panel in series would be 94 volts, please advise

0

## Comments

4,253✭✭✭✭The advise would be to combine at the panels and run a single line. I would guess you have 72 cell panels and the 94 volts is a VOC number? if you are calculating voltage drop I would use the VMP numbers.

34✭✭as far as the voc each panel voc is 47 volts I was going to make 2 string of 2 each 47*2=94 and run the two set of cables to the combiner

4,253✭✭✭✭Actually for just 2 strings you don't need a combiner box, you can just use a couple branch connectors;

4,253✭✭✭✭34✭✭258✭✭✭34✭✭PERFORMANCE UNDER STANDARD TEST CONDITIONS (STC)* Maximum power Pmax

325 Wp Open circuit voltage Voc 47.0 V Maximum power point voltage Vmpp

37.7 V Short circuit current Isc 9.28 A Maximum power point current

Impp 8.68

4,253✭✭✭✭With a VOC of about 94 with 2 panels in series, I would assume a VMP of about 74. So the amps of a string of 2 would be wattage 650/74=8.8 amps 2 strings would be 17.6 amps at 74 volts, with a run of 120 feet on 8 gauge wire.

Now I have the needed number to drop into a voltage drop calculator, like this one;

http://www.calculator.net/voltage-drop-calculator.html

Rendered results above that which would be desirable, but not too ugly.

The voltage is high enough that you will still be able to charge a 48 volt battery bank with a PWM charge controller. Assuming the VMP is correct or close.

You can swap out numbers here;

http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=2.061&voltage=74&phase=dc&noofconductor=1&distance=120&distanceunit=feet&eres=17.6&x=58&y=20

Using the NOCT (Normal Operating Cell Temperature) values for a 325 watt Canadian Solar panel, the voltage drop during real world use would be about 3%;

https://ressupply.com/solar-panels/canadian-solar-cs6u-325p-pt-maxpower-solar-panel-pallet?gclid=Cj0KCQjwm9vPBRCQARIsABAIQYeeu3SiaY4WT_aW2xcwf_5uYcJIBfFqmBs2GKlunBJtUOb4zlfIPY4aAms9EALw_wcB

The voltage drops when panels are hot and normal wattage will be about 75% of the panel's rating;

34✭✭using the calculator i get

## Result

Voltage drop:5.28Voltage drop percentage:

7.88%Voltage at the end:

61.72Please note that the result is an estimation based on normal condition. The actual voltage drop can vary depend on the condition of the wire, the conduit being used, the temperature, the connector, the frequency etc. But, in most cases, it will be very close.

4,253✭✭✭✭I did my calculations working backwards from the 650 watt string of 2 panels;

So my number represented all 4 panels."With a VOC of about 94 with 2 panels in series, I would assume a VMP of about 74. So the amps of a string of 2 would be wattage 650/74=8.8 amps 2 strings would be 17.6 amps at 74 volts, with a run of 120 feet on 8 gauge wire."