Document: NUREG-0800
Document ID: a9242e96-646c-405b-bcbe-0f249e45b75c
Document Type: srp
Title: Appendix 7-A
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0525/ML052500544.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
owered in accordance with the guidelines of Reg. Guides 1.75 and 1.153. If non-safety power sources interface to the isolation device, the applicant/licensee should verify that the non-safety power is not required for the device to perform its isolation function. Maximum credible fault (MCF) requirements should be established by analysis of proximate circuits that are 1 credible sources of the fault, either through inadvertent application through human error or through a fault or failure postulated to occur that involves proximate circuits, cabling, or terminations (for example, a "hot short" from an adjacent conductor). The determination of specific MCF characteristics is plant-specific. Rev. 4 — June 1997 Appendix 7-A BTP HICB-11-4 The surge waveforms and characteristics should be defined for the worst-case conditions expected at the installation. The acceptable leakage current into the safety system should be identified for specified MCF. Description of Device Design The design of isolation devices should conform to ANSI/IEEE Std 279 and Reg. Guides 1.75 and 1.153 guidelines for: (1) independence of redundant safety divisions, and (2) independence between protection (safety) and control (non-safety) systems. The isolation device should include design features for which credit is taken (e.g., surge protectors or barriers) and identification of the application limits of the device. The device should be designed for postulated electrical faults or failures, including open circuits, short circuits, ground, and application of an MCF. The specified MCF should equal or exceed the application requirements. Reg. Guides 1.75 and 1.153 suggest that the MCF include the levels and duration of the fault current on the non-safety side of the device. ANSI Std C84.1, "American National Standard for Electric Power Systems and Equipment — Voltage Ratings (60 Hz)," Table 1, "Standard Nominal System Voltages and Voltage Ranges," provides an acceptable basis for identifying