Document: NRC Regulatory Guide
Document ID: 8e45dce1-e1e7-4415-b1dd-7e2a610e545b
Document Type: regulatory_guide
Title: Fire Protection for Nuclear Power Plants (Rev. 4)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2023/ML20231A835.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.189
CFR Part: 
CFR Title: 

Content:
of Associated Circuits of Concern The shutdown capability may be protected from the adverse effect of damage to associated circuits of concern by the separation and protection guidelines of Regulatory Position 5.3 of this guide (or Regulatory Position 6.1.1.1 for cables inside a noninerted containment) or, alternatively, by the following methods, as applied to each type of associated circuit of concern. 5.4.4.1 Common Power Source It may be necessary to coordinate a load fuse or breaker (i.e., interrupting devices) with a feeder fuse or breaker to prevent the loss of the redundant or alternative shutdown power source. IEEE Standard 242 provides detailed guidance on achieving proper coordination. To ensure that the coordination criteria are met, the following should apply: a. The time-overcurrent trip characteristic for all circuit faults associated with the interrupting devices (breakers or fuses) of the circuit of concern should cause the interrupting device to interrupt the fault current before initiation of a trip of any upstream interrupting device that will cause a loss of the common power source. b. The power source should supply the necessary fault current for enough time to ensure the proper coordination without loss of function of the shutdown loads. The acceptability of a particular interrupting device can be demonstrated by meeting the following criteria: a. The interrupting device design should be factory tested to verify overcurrent protection, in accordance with the applicable UL, ANSI, or National Electrical Manufacturers Association standards. b. For low- and medium-voltage switchgear (480 V and below), periodic testing of circuit breakers and protective relays should demonstrate that the overall coordination scheme remains within the DG-1359, Page 88 limits specified in the design criteria. This testing may be performed as a series of overlapping tests. c. Molded case circuit breakers should periodically be manually exercised and inspected to ensure