What size cable tube should I choose for photovoltaic panels

Why 10-American-Wire-Gauge (AWG) is selected as the standard for external connection of solar arrays due to the following:Oversized for safety & voltage dropLow resistance for solar current of 30 Amps per single panelThe voltage drop over distance is lowCable is flexible [pdf]
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How big is the cable of the photovoltaic area combiner box

Use 4–10 mm2, 600 V insulated cables. Strip 8 mm of cable insulation. Ground the combiner box by connecting it to the inverter. Use the grounding points marked with the Open the combiner box cover. [pdf]
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