240.21(C)(4)

[Dale001289]

Is there any reason to add 25% to transformer secondary conductors? For example the engineer is saying if the MCB is rated 1200A in the SWGR, you need the secondary conductors to be rated 1200A x 1.25% = 1500A. But I see no evidence of that in 240.21(C)(4)


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[infinity]

No. You can size the secondary conductors based on the OCPD where they terminate. You just cannot use the next size up rule for conductors 800 amps or less.

 

[petersonra]

Well, it is going to come out that way, or close to it if you use the maximum secondary ocpd rating.

Suppose you had a 1500 amp ocpd rating on the secondary. What would the rating of necessary conductors be.

 

[Dale001289]

No. You can size the secondary conductors based on the OCPD where they terminate. You just cannot use the next size up rule for conductors 800 amps or less.

Thanks infinity


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