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:
immediately after the fire endurance test to assess the cable insulation resistance levels. This testing will ensure that the cables will maintain the insulation resistance levels necessary for proper operation of instruments. The Megger tests (pre-fire, during the fire (if performed), and immediately after the fire test conditions) should be done conductor-to-conductor for multiconductor cables and conductor-to-ground for all cables. The minimum acceptable insulation resistance (IR) value, using the test voltage values as shown in Table B-1 (below), is determined by using the following expression: DG-1359, Appendix B, Page B-7 IR (mega-ohms) = {[K+1 mega-ohm] * 1000 (ft)}/length (ft) where K = 1 mega-ohm/kV * operating voltage (expressed in kilovolts (kV)) In addition, to determine the IR levels required for nuclear instrumentation cables, the minimum IR value (e.g., 1 mega-ohm) and its potential impact on the functionality of these cables should be evaluated. An AC or DC Hi-Pot test for power cables greater than 1,000 V should also be performed after the post-fire Megger tests to assess the dielectric strength. This test provides assurance that the cable will withstand the applied voltage during and after a fire. The Hi-Pot test should be performed for a 5-minute duration at 60 percent of either 80 V/mil AC or 240 V/mil DC (e.g., 125-mil conductor insulation thickness × 240 V/mil DC × 0.6 = 18,000 V DC). Table B-1 summarizes the Megger and Hi-Pot test voltages that, when applied to power, control, and instrumentation cables, would constitute an acceptable cable functionality test. Table B-1. Functionality Test Voltages TYPE OPERATING VOLTAGE MEGGER TEST VOLTAGE HIGH-POTENTIAL TEST VOLTAGE Power >1,000 V AC 2,500 V DC 60% × 80 V/mil (AC) 60% × 240 V/mil (DC) Power <1,000 V AC 1,500 V DC1 None Instrument and Control <250 V DC <120 V AC 500 V DC None The review guidance for Megger and Hi-Pot test voltages was derived from Institute of Electrical and Electronics