Document: NUREG-0800
Document ID: c81bfd3b-114e-4701-a558-e08d57d14fd5
Document Type: srp
Title: D provides additional guidance.
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1515/ML15159A769.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7.1
CFR Part: 
CFR Title: 

Content:
the guidelines of RG 1.75. If nonsafety power sources interface to the isolation device, the applicant or licensee should verify that the nonsafety power is not required for the device to perform its isolation function. MCF requirements should be established by an analysis of proximate circuits that are credible sources of the fault, either through inadvertent application from human error or through a fault or failure postulated to occur that involves proximate circuits, cabling, or terminations (e.g., a “hot short” from an adjacent conductor). The determination of specific MCF characteristics is plant- specific. 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 MCFs. Description of Device Design The design of isolation devices should conform to IEEE Std 603-1991, or IEEE Std 279-1971, and RG 1.75 guidelines for: (1) independence of redundant safety divisions, and (2) independence between protection (safety) and control (nonsafety) 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. RG 1.75 suggests that the MCF include the levels and duration of the fault current on the non-safety side of the device. American National Standards Institute (ANSI) Std C84.1-1989, Table 1, “Standard Nominal System Voltages and Voltage Ranges,” provides an acceptable basis for identifying nominal voltages and guidelines for steady-state tolerances. BTP 7-11-6 Draft Revision 6 – August 2015 The device design should accommodate the fault voltage and current waveforms and