Document: NUREG-0800
Document ID: 81256f55-72dd-4777-9472-f373c71c4554
Document Type: srp
Title: AC POWER SYSTEMS (ONSITE)
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070550065.pdf
Revision Date: 2023-06
Chapter: 8
Section ID: 8.3.1
CFR Part: 
CFR Title: 

Content:
eted before June 1, 1973. Position C.3 of this Regulatory Guide does not recommend the sharing of onsite power systems between nuclear units for construction permit applications docketed after June 1, 1973. Further details of the review with regard to Position C.2 on sharing of the onsite power system between units are covered in item 4, below. [For new plants, sharing of diesel generators between units is not recommended.] B. The interconnections between redundant load centers through bus tie breakers and multi-feeder breakers used to connect extra redundant loads to either of the redundant distribution systems are examined to ensure that no single failure in the interconnections will cause the paralleling of the standby power supplies. To ensure this, the control circuits of the bus tie breakers or multi-feeder breakers should preclude automatic transferring of load centers or loads from the designated supply to the redundant counterpart upon loss of the designated supply (Position D.4 of Regulatory Guide 1.6). Regarding the interconnections through bus tie breakers, an acceptable design should provide for two tie breakers connected in series and physically separated from each other in accordance with the acceptance criteria for separation of the onsite power system, which is discussed below. Further, the interconnection of redundant load centers should be accomplished only manually. With respect to the interconnections through the multi-feeder breakers supplying power to extra redundant loads, the review relates to the use of the extra redundant unit as one of the necessary operating units (if the substituted-for-normal unit is inoperable). If this is the selected mode of operation prior to an accident concurrent with the loss of offsite power, it is verified by reviewing the breaker arrangement and associated control circuits to ensure that no single failure in the feeder breaker that is not connected to the extra redundant unit could cause the closing of this