3 conductor cable question

[bigpapa400lb]

A 4600 volt4/0 three conductor copper cable is in isolated conduit in air. What is the maximum allowable rating of a circuit breaker used to protect the ungrounded conductors?

The answer says 1200 Amperes
Ref: Table 310.75 & 240.101(A)
What is confusing me 240.101(A) says that the breaker cannot be six times the ampacity of the conductor.

Table 310.75
4/0 255A 90 c (Column)
285A 105 c (Column)

How do you get the 1200A?

 

[Joe Villani]

3 conductor cable question

255 times 6 equals 1530

next standard size ocpd not exceeding 1530 amps is 1200 as per 240.6(A)

 

[chris kennedy]

255 times 6 equals 1530

next standard size ocpd not exceeding 1530 amps is 1200 as per 240.6(A)

...........

240.1 Scope.
Parts I through VII of this article provide the general requirements for overcurrent protection and overcurrent protective devices not more than 600 volts, nominal. Part VIII covers overcurrent protection for those portions of supervised industrial installations operating at voltages of not more than 600 volts, nominal. Part IX covers overcurrent protection over 600 volts, nominal.

 

[bigpapa400lb]

Thanks for the help