Mike Dolt Enterprises
Mike Dolt Enterprises
User: PJS3, Location: Lockport, IL
Asked on: Thursday, March 24, 2011 at 10:58 am EDT
Answered on: Tuesday, May 14, 2024 at 3:12 am EDT
Question: There is a debate between me and my colleagues regarding this section of the 2008 NEC.The scenario here involves an outdoor 3 phase, delta-wye transformer with conductors located outdoors that feeds into an ATS which is also located outdoors. The debate is whether or not over-current protection is required for the secondary conductors.Please join the discussion.
Section 240.21(B) of the 2008 NEC"Overcurrent protection for conductors of a transformer circuit shall be provided in accordance with 450.3 and 450.
4."Section 450.3(A)(1) of the 2008 NEC"Overcurrent protection shall be provided for each ungrounded conductor."Section 450.4(A)(1) of the 2008 NEC"Where the secondary of a transformer is delta connected and the primary is wye connected, the primary shall be considered a grounded system. The secondary shall be protected against overcurrent as specified in 450.3(A)."Based on these code sections, it is clear that over-current protection is required for the secondary conductors of an outdoor 3 phase, delta-wye transformer with conductors located outdoors that feeds into an ATS which is also located outdoors.
Additional Considerations
The over-current protection for the secondary conductors should be located as close as possible to the transformer secondary terminals. The over-current protection should be sized according to the transformer secondary current rating. The over-current protection should be installed in a readily accessible location. Flag for review