How is DC cable sizing and voltage drop calculated?

Easy PV returns the smallest cable cross-sectional area that achieves a voltage drop less than 1% of the voltage across the cable (or the largest cable if none do).

The voltage drop along a cable is the product of the current running through it and its resistance. We calculate cable resistances using the stranding class 1/1 and 2 values from the IEC 60228/BS 6360 stranding chart. 

Example calculation

InAdapt general,example we want thefrom cable resistancecalcs suchhere: that: 

I * R <  1% change 

In this example, we have current at 12 A.  Voltage at 157V so 1% is 1.57V So we have:

12A * R < 1.57V
R < 1.57 https:/ 12 = 0.1308

For the cable sizes in Easy PV (4, 6, 10 mm²), we have the following: 

Resistance at 20	Resistance at 40	Ohms per m (rather than km)
4.61	4.972346	0.004972346
3.08	3.322088	0.003322088
1.83	1.973838	0.001973838

/docs.google.com/spreadsheets/d/1me9UIuyPfioQQbOrTBsFxSda4AY5mMhxSHBCOlgdLqw/edit?gid=0#gid=0