Transformer secondary conductors protection 240.21 (C)

[zemingduan]

I want to make sure I understand the 240.21(c) correctly, so I ask this question. Do all design below comply with 240.21 (C) ? This is not an industrial installation. The transformer primary fuses are 80E.




In my opinion, all the three design meet the table 450. 3 (A). Someone think, in design 1 the 3000A secondary conductors are not protected by any OCPD and in design 2 the 3000A switchboard bus is not protected by any OCPD. But I think design 1&2 meet 240.21(c) (2) since the 240.21(c) (2)(1) (b) doesn't require the secondary conductors must terminate in a single circuit breaker or set of fuses.

I think NEC should add the wording " The secondary conductors shall terminate in a single circuit breakers or set of fuses" to 24.21(C)(2) as similar wording as 240.21(C)(6)(2) if they require a separate OCPD for the 3000A secondary conductors in design 1 and the 3000A bus in design 2. Let me know your ideas!

 

[zemingduan]

The total calculated loads feed by the transformer is less than 3000A.

 

[jim dungar]

In my opinion, all the three design meet the table 450. 3 (A).

There is no reason to even look at 450.3. The OP was about 240.21(C).

All of the designs meet 240.21.

But 450.3 is satisfied because the primary side is less than 125%, therefore the secondary side is immaterial.