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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Photovoltaic panel cable fixing

Fixing Loose Connections: A Step-by-step GuideStep 1: Ensure Safety Switch off the PV system before you begin the processStep 2: Locate the Loose Connection This could be within a junction box, at a connector, or between a cable and an inverterStep 3: Tighten the Screw Terminal . Step 4: Check Friction-fit Connectors . Step 5: Re-check the Connection . Step 6: Monitor the Repaired Connection . [pdf]