How do I select 4160V cable for medium voltage feeder using Vacuum Contactor (V-Contact)protection. Is it the same rule like 125% of FLA? Please advise.
NEC 430-6 and 430-22 do not seem to exclude medium-voltage motors, but Table 430-150 does not have a 4000-volt column, implying the need to interpolate/extrapolate published values. The 90°C values in Tables 310-76 and 310-80 seem to safely be conservative. It may be desirable to avoid the 105°C column, for termination/splice reliability may become an issue.
For medium voltage motors and controls, skimping on cable sizes and connectors would seem far more suicidal than for low voltages.
In spite of complain with NEC 430, voltage drop at full load and starting should be considered while selecting the conductor size to feed an electric motor.
