When you zip-tie 10 current-carrying conductors together in a conduit, they trap heat. The NEC requires a "bundling derating factor" – often as low as 70% for 7-9 conductors. A cable that is perfectly rated in free air is dangerously undersized inside a packed raceway.
The most common mistake is thinking that cable sizing is only about current carrying capacity (ampacity). It’s actually a balancing act of three competing physics problems: copper cable sizing
NEC (National Electrical Code) and IEC standards agree: A cable should not be continuously loaded (3+ hours) above 80% of its rated ampacity. When you zip-tie 10 current-carrying conductors together in
$I_z \ge I_b / (k_1 \times k_2 \times k_3)$ The most common mistake is thinking that cable
Real-world example: A 15A pump, 200 feet from the panel on 120V. Using 14 AWG (common for 15A) gives a 7.2% voltage drop. That pump will fail. You must jump to 10 AWG to drop to 2.8%.
Check the $6 \text mm^2$ cable.