circuit breaker sizing below 800A

[ENDIX]

based on NEC 240.4. C , state that the ampacity of the conductors shall be equal to or greater than the rating of the overcurrent device, that has rating 800 rated over.
is it mean that for current below 800 A, is allowed to use overcurrent device that greater than ampacity of the cable?? (except for cable size 10 AWG and smaller has state on 240.4 D)

thanks

 

[iwire]

is it mean that for current below 800 A, is allowed to use overcurrent device that greater than ampacity of the cable??

Yes.

Below 800 amps you may use the next larger standard size overcurrent protection size listed in 240.6

For instance 500 kcmil copper has a usable ampacity of 380 amps.

The next standard size overcurrent protection is 400 amps so we could use a 400 amp overcurrent device.

However the calculated / connected load can not exceed the rating of the conductors.

 

[busman]

Be sure you look at the requirements of 240-3(b).

There are 2 other conditions to be met.

Mark