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:
teria are met. Of critical importance is the use of certain robust design criteria outlined in NEI 00-01, Revision 4, Appendix B.1, that ensure HIFs do not persist in an electrical system for extended periods of time. These criteria include the use of properly coordinated protective devices as outlined in IEEE 242, “IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems” (Ref. 115), and the use of proper protective devices that are designed and constructed according to applicable industry standards and applied within their vendor ratings. Additionally, appropriate testing and maintenance should be performed on these protective devices by following accepted industry guidelines and specific vendor recommendations for maintenance and testing. The consensus position of the panel was that the guidance in NEI 00-01, Revision 4, Appendix B.1, can be safely applied to fire safe-shutdown methodologies throughout the plant. 5.3.4 Open Secondary Circuits on Current Transformers Current transformers (CTs), a subgroup of instrument transformers, are used throughout AC electrical distribution systems in nuclear power plants to monitor current levels at select locations (e.g., cable, bus bar) and provide a signal from their secondary winding that is proportional to the current flowing through the main (primary) winding. In many cases, the protective relays and indicators associated with the CT are located at the same locations as the CT. For these cases, the secondary circuit is typically confined to the switchgear or equipment containing the CT. In other instances, the secondary circuit of the CT may provide a signal to remotely located protective relay(s) or indicator(s) (e.g., differential protective relays and remote ammeters). As such, the secondary circuit may span many fire areas within a nuclear power plant. These latter cases present a potential safety concern as an open circuit in a CT’s secondary can cause high crest