240.21(B), 240.21(B)(3), 240.21(C)(5)

[Dale001289]

I have an existing 480V feeder and want to tap off with feeder of equal size to a new dry-type transformer, 480-208/120V. The existing feeder is protected at 150AT CB (in MCC) and cable is #1/0. The installation is indoors. Proposed is #1/0 cable for tap conductors to the xfmr primary.
Are there any restrictions on the LENGTH of the tapped conductors?

Thanks in advance.

 

[Smart $]

#1/0 to #1/0 is a splice, not a tap. Please see definition of tap conductor in 240.2.

 

[infinity]

The original #1/0 feeder conductors are properly protected by the 150 amps OCPD, as Smart stated you're simply splicing on another set of #1/0's that will also be protected by the 150 amp OCPD so no tap rules apply.

 

[Dale001289]

The original #1/0 feeder conductors are properly protected by the 150 amps OCPD, as Smart stated you're simply splicing on another set of #1/0's that will also be protected by the 150 amp OCPD so no tap rules apply.

The xfmr is 45kVA at 3ph 480V on the primary = 54A x 250% = 135A, per 450.3(B) The existing breaker is 150AT, which is the next HIGHER size per 240.6....or do I need to round down to 125A, i.e. add a CB or fused disconnect on the primary side?

thanks in advance.

dale

 

[Smart $]

The xfmr is 45kVA at 3ph 480V on the primary = 54A x 250% = 135A, per 450.3(B) The existing breaker is 150AT, which is the next HIGHER size per 240.6....or do I need to round down to 125A, i.e. add a CB or fused disconnect on the primary side?

thanks in advance.

dale

Correct. You cannot go to next greater standard size on the primary when using primary and secondary protection.

Can you not just change out the 150A breaker with a 125A?

 

[Dale001289]

Correct. You cannot go to next greater standard size on the primary when using primary and secondary protection.

Can you not just change out the 150A breaker with a 125A?

I've presented this as an option; should get some feedback from Client by end of week.

Thanks for the advice.