United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. NO: 85-49: Relay Calibration Problem

                                                      SSINS NO.:  6835 
                                                         IN 85-49 

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                           WASHINGTON, D.C. 20555 

                                July 1, 1985 

Information Notice No. NO: 85-49:   RELAY CALIBRATION PROBLEM 

Addressees: 

All nuclear power reactor facilities holding an operating license (OL) or a 
construction permit (CP). 

Purpose: 

This information notice provides information on a potentially significant 
problem pertaining to relay orientation during calibration and operation. It
is expected that recipients will review the information for applicability to
their facilities and consider actions, if appropriate, to preclude a similar
problem occurring at their facilities. However, suggestions contained in 
this information notice do not constitute NRC requirements; therefore, no 
specific action or written response is required. 

Discussion: 

South Carolina Electric and Gas Company, at the Summer nuclear power plant, 
recently discovered that there was a significant error in the calibration of
several E-7000 series Agastat time-delay relays. The licensee's procedure 
for replacement of Agastat timing relays did not require calibration of 
these relays in the installed position. During relay replacement, these 
time-delay relays were "bench" calibrated in a horizontal position, then 
field mounted in a vertical orientation. Subsequent time-delay measurements 
determined that the delay times of the installed devices were as much as 30% 
greater than that established during "bench" calibration. 

Licensee investigation of this anomaly determined that the manufacturer's 
data sheet for installation and operation of these relays identifies a 
potential for the observed calibration error. This data sheet states that a 
dial calibration error may result if the device is mounted horizontally 
without the manufacturer's supplied horizontal operation options. Because 
these relays were mounted vertically at this facility, the potential for 
error as a result of horizontal "bench" calibration was overlooked. Because 
of this oversight, the licensee's relay replacement procedure did not 
specify device orientation during calibration. Several of these relays were 
functionally arrayed (sequentially or in parallel) in safety-related 
applications, such as in the emergency diesel generator undervoltage start 
circuitry. The above identified time-delay error went undetected for a 
period of approximately 4 months for some of these relays. This occurred 
because the licensee's replacement procedure specified only an operational 
or functional postmaintenance test of the system containing the relays. This 
method of testing did not detect the individual relay time-delay calibration 
errors. 

8506260654  
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                                                              IN 85-49     
                                                              July 1, 1985 
                                                              Page 2 of 2  

The licensee has subsequently revised their relay calibration procedures to 
calibrate or check the calibration of relays after mounting in place, where 
practical. The procedures were also revised to ensure "bench" calibrations 
are performed in the same orientation as mounted, where applicable. 
Personnel involved in relay calibration have received training on the 
revised procedures. 

No specific action or written response is required by this information 
notice. If you have any questions about this matter, please contact the 
Regional Administrator of the appropriate NRC Regional Office or this 
office. 


                                   Edward L. Jordan, Director
                                   Division of Emergency Preparedness
                                     and Engineering Response
                                   Office of Inspection and Enforcement

Technical Contact:  H. Bailey, IE 
                    (301) 492-9006 

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