IEC Cable Sizing

I would also be curious to know the answer to this.

Please let me know

Thanks

It depends on location.

NEC or IEC? Electrical Standards Listed by Country - E&S Grounding

My experience is that IEC is much more "relaxed" than NFPA 70 (as are many regulations in Europe compared with NFPA).

We Americans like the overkill safety factor.

“IEC is much more relaxed.”

It depends on where you are under the IEC banner. BS7671 is quite strict on earthing (grounding) requiring earth loop impedance testing and documentation, testing that the NEC doesn’t require.

Down here in NZ we are mostly IEC.

We wouldn't be required here to oversize a motor feeder by 125%. The feeder would be dimensioned based on motor FLA and feeder length where appropriate. The cables that are used here are broadly the same csa vs amapcity as in NEC-land too.

Another key difference is in the circuit breakers. For a motor circuit, the preferred circuit breaker (for smaller motors which can be protected with miniature circuit breakers) is a D-Curve which trips magnetically at 5x - 10x rated current and so can buck motor starting currents better than the C-Curve which is used for most other loads.

If in doubt, consult a qualified local Electrician. To do otherwise invites the risk of a measure of unpopularity with the facility's fire insurance cover provider.

Talk to the AHJ, as in authority having jurisdiction. When it comes down to it, their opinion is the one that matters. If you are in the US, you will most likely fall under the NFPA guidelines, I would hazard to guess Canada (and maybe Mexico?) would be similar. Outside of the Americas, you will most likely will fall under IEC purview. I can tell you, opinions from the internet are worth exactly what you paid for them. Get in touch with the local authorities. They can guide you better than we can.

Let's take an induction motor of 100 hp/460 V [122 A and 122*1.25=152 A]

and 75 kW 400 V [142 A rated].

Comparing NEC Table B.310.15(B)(2)(8) with IEC60364-5-52 Table A.52-5 (52-C4)

NEC 2 AWG[33.63 mm^2]161 A IEC 35 mm^2 144 A

The calculation theory are close: Nehrer&MacGrath vis-a-vis of IEC 60287.

NEC exudes the fragrance of democracy :less theory more practical.

So, the IEC is close to theoretical results while the NEC it is more practical.