An important element of assessment is the length of the cable. Each meter of the cable causes a voltage drop proportional to the value of the current that runs through it, if cosf = 1 we have: V = IxR.
V = voltage drop, I = current, R = resistance of the cable. In the case of inductive loads (solenoid valves, motors, etc.) or with variable currents, the higher current peak must be considered to avoid even temporary loss of power, which could hinder the proper functioning of the equipment. The longer is the cable, the greater the #voltage #drop, the IEC allows maximum values drop from 3% to 5% of rated voltage. Greater values are admitted only for the current peaks (e.g.: engines starting), if they do not create functioning problems. To minimize the voltage drop the cable section should be increased. Here are some tables that can help to easily calculate the minimum theoretical cable section. See tables 3 and 4 on the page http://www.shield.net/files/catalogue/support/2.2.pdf.For example, an average continuous current 1 A with section 0,34 mm2 and cable length 10 m generates a voltage drop of 1,3 V, which is approximately 5% of 24 V.
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