Information Notice No. 84-78: Underrated Terminal Blocks That May Adversely Affect Operation of Essential Electrical Equipment
SSINS No.: 6835
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
November 2, 1984
Information Notice No. 84-78: UNDERRATED TERMINAL BLOCKS THAT MAY
ADVERSELY AFFECT OPERATION OF ESSENTIAL
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP).
This information notice is to alert recipients of a potentially significant
generic problem involving the use of terminal blocks that have improper
voltage ratings. Using underrated terminal blocks may result in an
electrical fault that could lead to loss of essential electrical equipment.
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.
Underwriters Laboratories (UL) Standard 1059 (October 30, 1975) defines
stringent criteria to determine voltage ratings for terminal blocks.
Terminal blocks for general industrial use at 150, 300, and 600 volts must
be tested to the requirements of UL Standard 1059 to be UL listed. The
acceptance values of these tests are described in UL Standard 1059. Note
that some models of terminal blocks have undergone testing more stringent
than UL Standard 1059 to meet use-specific qualification requirements.
On May 4, 1984, under the provisions of 10 CFR 50.55(e), Detroit Edison
reported a potential deficiency concerning underrated motor terminal blocks
manufactured by Vernitron Incorporated (Beau Products Division) and
installed in some Limitorque valve operators at Fermi
November 2, 1984
Page 2 of 2
Unit 2. The specific installation identified involved the use of Beau
Products 76000 series terminal blocks in type SMC-04 Limitorque valve
operators. The terminal blocks were being used in 480-V ac motor
terminations; but, according to the terminal block manufacturer, the
terminal blocks have a UL rating of 150 volts for general industrial use.
In the absence of any other qualification testing of the suspect terminal
blocks, there is a possibility of electrical shorting that could result in
the failure of the motor to operate when required. Failure of the motor to
operate could compromise the function of the safety system of which the
valve is an integral part.
Limitorque Corporation has stated that the Beau Products 76000 series
terminal blocks, have been used only in the SMC-04 model valve operator. In
addition, Limitorque has stated that there have been no failures reported as
a result of the Beau Products terminal blocks in question. The licensee at
Fermi Unit 2 is replacing the affected Beau Products terminal blocks.
It is suggested that the facility review of this information include other
types of terminal blocks and equipment for similar applications. 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: J. C. Stewart, IE
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