United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No.80-08 – The States Company Sliding Link Electrical Terminal Block

                                                            SSINS: 6870 
                                                            Accession  No.:
                                                            7912190689

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

                               March 7, 1980  

                                           Information Notice No. 80-08 

THE STATES COMPANY SLIDING LINK ELECTRICAL TERMINAL BLOCK 

Description of Circumstances: 

On July 19, 1979, the Consumers Power Company notified the Nuclear 
Regulatory Commission of a defect found in the sliding link electrical 
terminal block manufactured by the States Company, a subsidiary of Multi Amp 
Corp. The defective terminal blocks were found at the Midland plant. 

The connection between the two slotted bars on the terminal block is made by
a U-shaped sliding link and spacer located between the two bars. The top of 
the U-shaped link and the spacer are drilled and the bottom of the link is 
threaded to accept a 8-32 screw. When the screw is tightened it binds the 
link, spacer and bar together to make electrical connection. Loosening the 
screw and sliding the link from between the bars breaks the connection. The 
purpose of the link is to provide easy insertion of test instruments, etc. 
into the circuit. 

The defect, which has been identified in 5% of the terminal blocks checked, 
occurs in the form of a crack between the threaded screwhole and the side of
the U-shaped link. When the screw is tightened the crack widens and a poor 
or intermittent electrical connection can result. A defective link is 
impossible to cinch tightly in place and is difficult to detect visually. 

Enclosure 1 shows the States Company terminal block. The defect, a crack in 
the bottom portion of the metal U-shaped link, is displayed in the exploded 
view of the terminal block assembly. These terminal blocks are widely used 
in the nuclear industry and may be used as permanent installations in safety
related systems. The defective mechanical connection can cause an electrical
circuit malfunction. 

This Information Notice is provided to inform licensees of a potentially 
significant matter. It is expected that recipients will review the 
information for applicability to their facilities. No written response to 
this Information Notice No. is required. However, the reporting requirements 
as set forth in the regulations must be met. If you require additional 
information regarding this matter, contact the Director of the appropriate 
NRC Regional Office. 

Enclosure: 
Graphic Display of Terminal 
     Block

Page Last Reviewed/Updated Tuesday, November 12, 2013