Table one of Ch 9 says if we have one conductor we can fill the conduit to 53%, 2 conductor to 31% and more than 2 conductors the conduit can be filled to 40%.
My question is why 31% for 2 conductors and 40% for more than 2 conductors? what is rational behind it.

An IAEI instructor once told me it is because of the heat dissipation. But he did not explain in details why?

Thanks.

Be kind to your neighbor, he knows where you live