Foreword?This standard provides criteria and requirements for establishing and maintaining the independence of Class 1E equipment and circuits and auxiliary supporting features by physical separation and electrical isolation. This 1992 revision of IEEE Std 384-1981@ IEEE Standard Criteria for Independence of Class 1E Equipment and Circuits@ reflects the results of separation testing completed by the nuclear industry on internally generated electrical faults. The working group has performed the following activities: 1) Assessed completed industry test reports to determine their applicability in support of changes in separation distances and reported these results to the Nuclear Power Engineering Committee (NPEC). 2) Conducted a panel discussion on the test results at the 1988 Institute of Electrical and Electronics Engineers (IEEE) Winter Power Meeting. 3) Presented a technical paper on the test results at the 1989 IEEE Winter Power Meeting (IEEE Paper No. 90 WM 254-3EC). The working group's review has resulted in changes to Section 6. of the standard as follows: 1) Separation distance criteria for congurations identied in IEEE Std 384-1981 have been reduced in some cases. In other cases@ insuficient testing data were available to support reducing the distances in IEEE Std 384-1981. 2) Separation distance criteria for congurations not addressed in IEEE Std 384-1981 have been added to the standard based on test results. These congurations include cable trays and conduits@ cable trays and cable in free air@ and conduits and cable in free air. Other sections of this standard have been reviewed@ and many editorial improvements have been made. As part of this work@ the working group assessed Nuclear Regulatory Commission (NRC) Regulatory Guide 1.75@ Revision 2@ which endorses IEEE Std 384-1974. A Request for Interpretation of IEEE 384-1977@ Paragraph 6.1.2 (now 7.1.2)@ was received by the working group regarding the phrase "maximum credible voltage or current transient." A definition of this phrase has been added to the standard. A request for proposed revision from the DC Auxiliary Power Working Group (Nuclear Power Subcommittee of the Power Generation Committee) was received regarding the use of fuses as isolation devices in power circuits. The standard has been revised to permit the use of fuses as isolation devices in power circuits. Section 8 of IEEE Std 384-1981 was previously included to provide interim criteria for implementation of independence requirements for safe shutdown systems required for exposure fires. 10 CFR 50@ Appendix R has since been issued to provide the requirements for safe shutdown; consequently@ Section 8 has been eliminated from the present issue of this standard. The Working Group has received suggestions and recommendations regarding the application of fiber optic cabling to Class 1E circuits. However@ to date@ there have been no analyses or test programs submitted to the Working Group to support special criteria for separating these cables in a manner different than already provided by considering them equivalent to typical instrumentation cable. If sufficient information becomes available to justify special separation criteria@ the Working Group will consider adding this criteria to the standard in a future revision. The IEEE has developed these criteria to provide guidance in the determination of the independence requirements related to the class 1E systems of the nuclear facility. Adherence to these criteria may not suffice for assuring the public health and safety@ because it is the integrated performance of the structures@ the fluid systems@ and the instrumentation and electric systems of the station that establish the consequences of accidents. Failure to meet these requirements may be an indication of system inadequacy. Each applicant has the responsibility to assure himself and others that this integrated performance is adequate.The Working Group feels that the criteria herein represent an industry and government consensus for ascertaining the adequacy of the independence of Class 1E systems.This standard describes the independence requirements of the circuits and equipment comprising or associated with Class 1E systems. It sets forth criteria for the independence that can be achieved by physical separation and electrical isolation of circuits and equipment that are redundant@ but does not address the determination of what is to be considered redundant.