GreenNGold
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I was hoping someone could help me interpret Table 450.3(B) - Note 1 in the NEC.
The note states: "Where 125 percent of this current does not correspond to a standard rating of a fuse or nonadjustable circuit breaker, a higher rating that does not exceed the next higher standard rating shall be permitted."
What does it mean when they say: "a higher rating that does not exceed the next higher standard rating shall be permitted"?
I am looking at an example of a 12,470V/7200V - 277/480V, 300KVA transformer. The secondary current is 360.84 Amps (300KVA /(1.73*480)). If there is primary and secondary protection 360.84 * 1.25 = 451 Amps. Why do we chose 450A as the secondary protection rather than 500A?
When Note 1 is called out, how do we know to go to the next higher or next lower standard value?
Thank you.
The note states: "Where 125 percent of this current does not correspond to a standard rating of a fuse or nonadjustable circuit breaker, a higher rating that does not exceed the next higher standard rating shall be permitted."
What does it mean when they say: "a higher rating that does not exceed the next higher standard rating shall be permitted"?
I am looking at an example of a 12,470V/7200V - 277/480V, 300KVA transformer. The secondary current is 360.84 Amps (300KVA /(1.73*480)). If there is primary and secondary protection 360.84 * 1.25 = 451 Amps. Why do we chose 450A as the secondary protection rather than 500A?
When Note 1 is called out, how do we know to go to the next higher or next lower standard value?
Thank you.