Generator Feeder Cable Sizing ?

[Shazim]

If a standby generator is sized with a typical safety margin of 30%, knowing that there is no additional load in the future,
why is it that the feeder cables are still sized based on 115% of the generator size ? In my view this is an oversize and comes down to engineering economics.
Please share your views.

 

[augie47]

Note that the 115% applies to the conductors to the 1st overcurrent device so this is often in the generator itself.
Once you leave that 1st overcurrent device the feeder can be sized per Art 215 but must be protected at it's ampacity per 240.4