Document: NUREG-0800
Document ID: d9e9d0a9-6390-4154-94dc-7d5e6d8145cd
Document Type: srp
Title: A-C POWER SYSTEMS (ONSITE)
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052350489.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8.3.1
CFR Part: 
CFR Title: 

Content:
ite power system from the offsite power system when required. The scope of the review for independence extends from the supply breakers connected to the low side of the unit auxiliary transformers and startup transformers (referred to as the offsite or preferred power supplies) to the station safety-related distribution system. The number and capability of electrical circuits from the offsite power system to the safety buses are to be consistent with satisfying the requirements of General Design Criterion 17. Then, downstream of the offsite power breakers at the safety buses, the design must- satisfy the requirements for redundancy and independence of General Design Criteria 34, 35, 38, 41 and 44; that is, for onsite power system operation (assuming offsite power is not available), the I system safety function can be accomplished assuming a single failure. To determine that the physical independence of the preferred power circuits to the Class lE buses is consistent with satisfying the requirements of General Design Criterion 17 and IEEE Std 308, the 8.3.1-10 Rev. 2 - July 1981 physical arrangement drawings are examined to verify that each circuit is physically separate and independent from its redundant counterparts. In addition, the final feeder-isolation breaker in each circuit through which preferred power is supplied to the safety buses must be designed and.physically separated in accordance with the requirements for the onsite power system.. Following the loss of preferred power, the safety buses are powered solely from the standby power supplies. Under this situation, the design of the feeder-isolation breaker in each preferred power circuit must preclude the automatic connection of preferred power to the respective safety bus upon the loss of standby power. In this regard an acceptable design will include the capability for restoring preferred power to the respective safety bus by manual actuation only. In assessing the adequacy of the electrical ties