Bulletin No. 88-10: Nonconforming Molded-Case Circuit Breakers
OMB No.: 3150-0011
NRCB 88-10
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
November 22, 1988
NRC Bulletin No. 88-10: NONCONFORMING MOLDED-CASE CIRCUIT BREAKERS
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
The purpose of this bulletin is to request that addressees take actions to
provide reasonable assurance that molded-case circuit breakers (CBs), in-
cluding CBs used with motor controllers, purchased for use in safety-related
applications without verifiable traceability1 to the circuit breaker manu-
facturer (CBM) (1) perform their safety functions.
Description of Circumstances:
NRC Information Notice No. 88-46, "Licensee Report of Defective Refurbished
Circuit Breakers," dated July 8, 1988 and Supplement 1 thereto, dated July 21,
1988, discussed a report by Pacific Gas and Electric Company that indicated
that its Diablo Canyon Nuclear Power Plant was supplied 30 CBs by Anti-Theft
Systems, Inc. through a local electrical distributor. These CBs (Square D
molded-case, type KHL 36125) were intended for use in non-safety-related
applications at the Diablo Canyon Nuclear Power Plant. Square D Company
reported that an inspection and testing of these breakers determined that the
CBs were refurbished Square D Company equipment. Furthermore, Square D
reported that several of the circuit breakers tested did not comply with
Square D or Underwriters Laboratories, Inc. (UL) specifications for all of the
electrical tests performed. Information Notice No. 88-46 also listed several
California companies that were involved in supplying surplus refurbished and
possibly defective refurbished electrical equipment to the nuclear industry.
During recent NRC inspections, additional examples were identified that
indicate a potential safety concern regarding electrical equipment supplied to
nuclear power plants. The NRC is concerned that equipment being procured as
new and assumed to meet all applicable plant design requirements and/or
original manufacturer's specifications may, in fact, not conform to these
requirements and specifications.
(1). Refer to Attachment 2 for Definition of Terms
8811180315
. NRCB 88-10
November 22, 1988
Page 2 of 7
The actions requested in this bulletin are limited to molded-case CBs.
Molded-case CBs are tested and calibrated at the manufacturer's plant in
accordance with recognized industry standards, such as UL-489, "Molded Case
Circuit Breakers and Circuit Breaker Enclosures," and National Electrical
Manufacturers Associ-ation (NEMA)-AB1, "Molded-Case Circuit Breakers." Since
molded-case CBs have factory-calibrated and sealed elements, any unauthorized
modification or refurbishing of these CBs could jeopardize their design
capability and reliability.
The NRC is concerned that the reliability and capabilities of refurbished CBs
purchased as commercial grade (non-Class 1E) for later upgrading to safety-
related (Class 1E) applications may not meet the minimum commercial grade
standards. In addition, the NRC is concerned about the reliability and capa-
bilities of commercial grade CBs upgraded to safety-related because of some
observed inadequacies in the dedication process and numerous failures found
during the testing of some of these CBs. In order to properly dedicate
electrical items procured as commercial grade for subsequent use in safety-
related applications, the dedication process should build from the commercial
grade quality, include a proper evaluation of seismic and environmental quali-
fication, confirm critical parameters, and include testing as appropriate.
Molded-case CBs purchased from the CBM or that can be traced to the CBM are of
lesser concern than other molded-case CBs because CBs from the CBM, whether
safety-related or commercial grade, are manufactured under controlled
conditions to conform to a proven design. Safety-related CBs purchased as
Class 1E from the CBM are controlled under quality assurance (QA) programs
that conform to Appendix B of 10 CFR Part 50. While upgrading programs may
vary in quality, the controls exercised by the CBM over the manufacturing
activities provide reasonable assurance that improperly refurbished components
have not been introduced and passed through the upgrading process.
Furthermore, the redundancy of safety systems and the in-service use of CBs
provide a reasonable basis for accepting installed replacement CBs that have
been procured from the CBM or that can be traced to the CBM.
The NRC currently believes that the concerns addressed in this bulletin do not
apply to electrical equipment (safety-related and commercial grade) originally
installed in plants. This equipment appears to have been procured during
plant construction from CBMs with full certification. The large quantities of
electrical assemblies or components procured under bid packages during plant
construction reduce the possibility of any original plant equipment being sup-
plied by vendors doing refurbishing.
Although the actions requested in this bulletin only apply to safety-related
molded-case CBs, the NRC intends to monitor industry programs to ensure that
other molded-case CBs, which may have been installed as replacements,
installed during modifications, or are being maintained as stored spares, are
suitable for their intended service. Addressees are encouraged to participate
in a joint program. If industry programs are either not timely or not
sufficient, additional regulatory actions will be taken, as appropriate.
. NRCB 88-10
November 22, 1988
Page 3 of 7
The NRC requested and received comments from the Nuclear Management and
Resources Council (NUMARC), the National Electrical Manufacturers Association
(NEMA), and the Underwriters Laboratories, Inc. (UL), during the preparation
of this bulletin. These comments were considered and some were appropriately
incorporated into this bulletin.
NEMA has commented to the NRC that determination of the critical performance
characteristics of durability and short-circuit capabilities of CBs requires
destructive testing of selected breakers that are representative of CBs to be
placed in service. Because a refurbished breaker may not have been
refurbished under controlled conditions to conform to a proven design,
destructively testing selected breakers will not infer anything about a
refurbished CB. UL provided specific comments on the tests in Attachment 1 of
this bulletin. In addition, they stated that, "it is UL's opinion that the
test program is not adequate to provide assurance that the tested,
non-traceable, circuit breakers would be suitable for their intended purpose."
Although the test program described in Attachment 1 of this bulletin does not
provide complete verification of all the performance requirements and
characteristics of molded-case CBs (such as seismicity or fault clearing
capability), the NRC considers the test program to provide a reasonable
assurance of performance requirements and characteristics most important to
ensuring reactor safety. This, considered in conjunction with (1) the limited
number of nonconforming CBs that may remain installed in safety-related
systems following implementation of the actions requested by this bulletin,
(2) the existence of redundant safety-related systems in nuclear power
reactors that are required by NRC regulations, (3) the license required
inservice testing of installed CBs performed to demonstrate the CB's
functional performance, and (4) the low frequency of occurrence of seismic
events and severe electrical faults, provides a reasonable assurance that
nuclear power reactors can be operated without undue risk to the health and
safety of the public.
The NRC investigation of this issue is not complete. A supplement to this
bulletin may be issued to include other electrical equipment or a longer pro-
curement review period if warranted by the results of the ongoing evaluations
or the results of testing requested in this bulletin.
Actions Requested:
1. All addressees are requested to perform the following review by March 1,
1989:
a. Identify all molded-case CBs purchased prior to August 1, 1988, that
are being maintained as stored spares for safety-related (Class 1E)
applications or commercial grade CBs that are being maintained as
stored spares for future use in safety-related applications; this
includes CBs purchased from a CBM or from any other source. If the
number of these stored spare CBs is less than 50 at a nuclear plant
site, then randomly select CBs purchased between August 1, 1983 and
August 1, 1988 that have been installed in safety-related applica-
tions as replacements or modifications to form a minimum sample of
50 CBs per nuclear plant site.
. NRCB 88-10
November 22, 1988
Page 4 of 7
b. Verify the traceability of these CBs.
c. Identify the number, manufacturer, model number, and to the extent
possible the procurement chain for all those CBs identified in (1a)
that cannot be traced to the CBM. For installed CBs, also identify
each system in which they are/were installed.
2. All holders of operating licenses who identify installed CBs per item 1
above or item 4 below that cannot be traced to a CBM are requested to
prepare, within 30 days of the completion of each item, an analysis
justifying continued operation until items 1 through 5 of the actions
requested in this bulletin have been completed.
3. All addressees who identify 80 percent or more CBs traceable to the CBM
per item 1 above are requested to test the CBs that are not traceable to
the CBM in accordance with the test program described in Attachment 1.
Any installed CBs that fail any of these tests should be replaced with
CBs that meet the criteria of item 7 of the actions requested or CBs that
pass all tests in accordance with the testing program described in
Attachment 1. If more than 10 percent of the CBs tested fail any of the
tests described in Attachment 1, continue with item 4; otherwise, proceed
to item 6 of the actions requested.
Holders of operating licenses are requested to complete this testing
program before startup from the first refueling outage beginning after
March 1, 1989. Holders of construction permits are requested to complete
this testing program before fuel load.
4. All addressees who identify less than 80 percent of the CBs traceable to
the CBM per item 1 above or who identify a failure rate of more than 10
percent for the CBs tested per item 3 above are requested to perform the
following actions:
a. Identify all molded-case CBs that have been purchased between August
1, 1983 and August 1, 1988, and installed in safety-related
applications as replacements or installed during modifications.
b. Verify the traceability of these CBs.
c. Identify the number, manufacturer, model number, system in which
they are/were installed, and to the extent possible, the procurement
chain for all those CBs identified in (4a) that cannot be traced to
the CBM.
5. All addressees who identify installed CBs that cannot be traced to the
CBM per item 4 above are requested to replace these CBs with components
that meet the criteria of item 7 of the actions requested or to test them
in accordance with the program described in Attachment 1; CBs that fail
any of these tests should be replaced with CBs that meet the criteria of
item 7 of the actions requested or CBs that pass all tests in accordance
with the test program described in Attachment 1.
. NRCB 88-10
November 22, 1988
Page 5 of 7
Holders of operating licenses are requested to replace or to test at
least one-half, or all if the total number is less than 75, of these
installed CBs before startup from the first refueling outage beginning
after March 1, 1989. The remaining CBs should be replaced or tested
before startup from the second refueling outage beginning after March 1,
1989.
Holders of construction permits are requested to replace or to test these
installed CBs before fuel load.
6. Information generated while performing the actions requested in items 1,
2, 3, 4, and 5 above should be documented and maintained for a period of
5 years after the completion of all requested actions.
7. With the exception of actions taken in response to items 3 and 5 of the
actions requested above, molded-case CBs installed in safety-related ap-
plications after August 1, 1988 should be:
a. Manufactured by and procured from a CBM under a 10 CFR 50, Appendix
B, program; or
b. Procured from a CBM or others with verifiable traceability to the
CBM, in compliance with applicable industry standards, and upgraded
to safety-related by the licensee or others using an acceptable
dedication program. The NRC encourages addressees to significantly
upgrade their dedication programs through a joint industry effort to
ensure their adequacy and consistency. The NRC will monitor these
industry initiatives and if they are not sufficient or not timely,
or if problems with the dedication of commercial grade equipment for
safety-related use continue, the NRC will take appropriate
regulatory actions.
8. Addressees that cannot meet the schedule for the actions requested above
and/or the corresponding reporting requirements below, should justify to
the NRC their proposed alternative schedule.
Reporting Requirements:
1. All holders of operating licenses are required to provide a written
report by April 1, 1989, that:
a. Confirms that only molded-case CBs that meet the criteria of item 7
of the actions requested are being maintained as stored spares for
future use in safety-related applications.
b. Summarizes the total number, manufacturer, model number, and to the
extent possible the procurement chain of those CBs that could not be
traced to the CBM in items 1 and 4 of the actions requested. For
installed CBs, also identify each system in which they are/were in-
stalled. If item 4 of the actions requested has not been completed
. NRCB 88-10
November 22, 1988
Page 6 of 7
by April 1, 1989, due to the schedule for tests in item 3 of the
actions requested, this information should be updated within 30 days
of the completion of item 4 to address those additional CBs that
could not be traced to the CBM.
c. Confirms that items 1, 2, 3, 4, 5, 6 and 7 of the actions requested
have been completed or will be implemented as requested.
2. All holders of operating licenses are required to submit a report that
summarizes available results of tests conducted in accordance with items
3 and 5 of the actions requested within 30 days after startup from the
first and second refueling outages beginning after March 1, 1989. For
CBs that pass these tests, the only information required is the number,
manufacturer, model number, and to the extent possible the procurement
chain of CBs tested (summary report format is acceptable). For CBs that
fail these test(s), these reports should indicate the test(s) and the
values of test parameter(s) at which the failure(s) occurred, as well as
the corresponding manufacturer, model number, and to the extent possible,
the procurement chain.
3. All holders of construction permits are required to provide a written
report by April 1, 1989, that:
a. Confirms that only molded-case CBs that meet the criteria of item 7
of the actions requested are being maintained as stored spares for
future use in safety-related applications.
b. Summarizes the total number, manufacturer, model number, and to the
extent possible the procurement chain of those CBs that could not be
traced to the CBM in items 1 and 4 of the actions requested. For
installed CBs, also identify each system in which they are/were
installed. If item 4 of the actions requested has not been com-
pleted by April 1, 1989, due to the schedule for tests in item 3 of
the actions requested, this information should be updated within 30
days of the completion of item 4 to address those additional CBs
that could not be traced to the CBM.
c. Confirms that items 1, 3, 4, 5, 6 and 7 have been completed or will
be implemented before fuel load.
4. All holders of construction permits are required to submit a report that
summarizes the results of tests conducted in accordance with items 3 and
5 of the actions requested within 30 days after fuel load. For CBs that
pass these tests, the only information required is the number,
manufacturer, model number, and to the extent possible, the procurement
chain (summary report format is acceptable). For CBs that fail these
test(s), the report should indicate the test(s) and the values of test
parameter(s) at which the failure(s) occurred, as well as the
corresponding manufacturer, model number, and to the extent possible, the
procurement chain.
. NRCB 88-10
November 22, 1988
Page 7 of 7
The written reports required above shall be addressed to the U. S. Nuclear
Regulatory Commission, ATTN: Document Control Desk, Washington, D.C. 20555,
under oath or affirmation under the provisions of Section 182a, Atomic Energy
Act of 1954, as amended. In addition, a copy shall be submitted to the ap-
propriate Regional Administrator.
This request is covered by Office of Management and Budget Clearance Number
3150-0011 which expires December 31, 1989. The estimated burden hour is 1000
to 10,000 man-hours per plant response, including assessment of these require-
ments, searching data sources, testing, and analyzing the data, and preparing
the required reports. Comments on the accuracy of this estimate and
suggestions to reduce the burden may be directed to the Office of Management
and Budget, Room 3208, New Executive Office Building, Washington, D.C., 20503,
and to the U.S. Nuclear Regulatory Commission, Records and Reports Management
Branch, Office of Administration and Resource Management, Washington, D.C.,
20555.
If you have any questions regarding this matter, please contact one of the
technical contacts listed below or the Regional Administrator of the
appropriate NRC regional office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: Paul Gill, NRR
(301) 492-0811
Jaime Guillen, NRR
(301) 492-1170
Attachments:
1. Test Program for Molded Case Circuit Breakers
2. Definition of Terms
3. List of Recently Issued NRC Bulletins
. Attachment 1
NRCB 88-10
November 22, 1988
Page 1 of 4
TEST PROGRAM FOR MOLDED-CASE CIRCUIT BREAKERS
1.0 Test Program Objectives
The objective of this proposed test program is to verify the reli-
ability and capabilities of molded-case circuit breakers (CBs).
For the safety of personnel and others involved with the activities
related to these proposed tests, appropriate safety practices, such
as ANSI/NFPA 70E, "Electrical Safety Requirements for Employee
Workplaces," Part II, should be followed.
These proposed tests have been based on tests described in industry
standards, such as NEMA AB-1, "Molded-Case Circuit Breakers," NEMA
AB-2, "Procedures for Field Inspection and Performance Verification
of Molded-Case Circuit Breakers Used in Commercial and Industrial
Applications," UL 489 "Molded Case Circuit Breakers and Circuit
Breaker Enclosures," and NETA STD ATS-1987, "National Electrical
Testing Association, Acceptance Testing Specifications."
2.0 Test Procedures for CBs
The following tests should be performed in the sequence listed. CBs
failing any of these tests should be considered unacceptable for
safety-related applications.
2.1 Mechanical Test
The CB should be operated, reset, and closed a minimum of five
times, to ensure that the latching surfaces are free of any binding.
2.2 Individual Pole Resistance or Millivolt Drop Test
(Ref. NETA STD ATS-1987 & NEMA AB-2)
The contact resistance of each pole of the CB should be measured at
ambient temperature. Three readings of each pole should be taken
with the CB operated without load between each reading. The average
of three readings for each pole should be calculated and compared
with the manufacturer's contact resistance data or with those values
of similar CBs from the same manufacturer. Also, the average value
for each pole should be compared with the average of the other poles
and the difference between the pole values should not exceed 50
percent of the lowest value; or
A millivolt drop test may be performed by applying a direct current
across the closed CB contacts and measuring the voltage drop due to
the contact resistance. The millivolt drop test should be performed
at room temperature. Direct current should be applied across each
. Attachment 1
NRCB 88-10
November 22, 1988
Page 2 of 4
pole and the millivolt drop and test current recorded for each pole.
Three readings of each pole should be taken with the CB operated
without load between each reading. The average of the three
readings for each pole should be calculated and compared with the
manufacturer's value for acceptance of the breaker.
2.3 Rated Current Hold-In Test (Ref. NEMA AB-1 & UL 489)
This test should be conducted at 100% rated current and at an
ambient air temperature of 25øC ñ 3øC, and followed by a test at
135% rated current and at an ambient temperature of 25øC ñ 3øC.
Equal 100% rated currents should be applied to all poles of the CB.
The CB must not trip within 1 hour for CBs rated 50 amperes or below
or within 2 hours for CBs rated over 50 amperes during this test.
At the end of the 100% rated current test, the current should be
increased to 135% and the CB should trip within 1 hour for CBs rated
50 amperes or below or within 2 hours for CBs rated over 50 amperes.
2.4 Overload Test (Ref. NEMA AB-1 & UL 489)
This test consists of one operating cycle (i.e., closing action
followed by an opening action) of the CB at 600% rated current.
This test may be conducted at low voltage. There should be no
electrical or mechanical breakdown of the CB during this test.
2.5 Instantaneous Trip Test (Ref. NEMA AB-1 & UL 489)
2.5.1 Fixed Instantaneous Setting CBs
Each pole of the CB should be tested for pickup of the instantaneous
unit. Each pole must be between 75% and 125% of the instantaneous
trip rating. The trip time should not exceed 0.1 seconds (6
cycles).
2.5.2 Adjustable Instantaneous Setting CBs
This test is the same as that in Section 2.5.1 except that each pole
must be tested at the lowest and highest settings.
The trip value for the lowest setting should be between 75% and 125%
of the lowest setting, and the highest setting should be between 80%
and 120% of the highest setting.
2.5.3 Short-Time Trip Setting Test
This test is applicable only if the CB is equipped with the short-
time delay trip. This test should be conducted at an ambient air
temperature of 25øC ñ 3øC. The operation of the short-time delay
unit should be within 90% and 125% of the overcurrent setting of
the CB as shown on the manufacturer's time-current curves.
. Attachment 1
NRCB 88-10
November 22, 1988
Page 3 of 4
2.6 Time Delay Overcurrent Trip (Ref. NEMA AB-2)
This test should be conducted at an ambient air temperature of
25øC ñ 3øC.
A current of 300% (at low voltage) of the marked rating should
be applied to each pole of the CB. The trip time for each pole
should be compared with the time shown in the CB manufacturer's
time-current curves. If the test trip times obtained for each pole
are not within the time band shown on the CB manufacturer's time-
current curves, then the test trip must not exceed the time
specified in Table 1 and the acceptance of the CBs must be evaluated
with the criteria listed below:
TABLE 1
VALUES FOR OVERCURRENT TRIP TEST
(AT 300% OF RATED CONTINUOUS CURRENT OF CIRCUIT BREAKER)
(REF. NEMA AB-2)
Breaker Range of Rated
Voltage Continuous Current Maximum Tripping
Volts Amperes Time In Seconds
240 15-45 50
240 50-100 70
600 15-45 70
600 50-100 125
240 110-225 200
240 250-400 300
600 110-225 250
600 250-400 300
600 450-600 350
600 700-1200 500
600 1400-2500 600
600 3000-5000 650
Minimum Tripping Time: If the minimum tripping times are lower
than indicated by the manufacturer's time-current curves for the
CB under test, the CB should be retested after it has been cooled
to 25øC. If the values obtained are still lower after retest, the
coordination with upstream and downstream CB should be evaluated.
If no problem with coordination is indicated, then the CB is ac-
ceptable.
. Attachment 1
NRCB 88-10
November 22, 1988
Page 4 of 4
Maximum Tripping Time: If the tripping time exceeds the maximum
tripping time shown on the manufacturer's time-current curves but
is below the time shown in Table 1, check the CB time against the
protection requirements of the circuit (such as cable, penetration,
etc.) to ensure that the CB provides the protection, as well as the
coordination with upstream and downstream CBs. If the CB provides
the necessary protection and coordination, then the CB is
acceptable.
Maximum Allowable Time: If the tripping time of the CB exceeds the
trip time shown in Table 1, the breaker is unacceptable for Class 1E
applications.
2.7 Dielectric Tests (Ref. NEMA AB-1 & UL-489)
The dielectric test should be conducted at an ac test voltage of
1760 volts (80% x [2 x rated voltage + 1000 volts]), or at 2500
volts dc for 1 minute withstand. The dielectric test should be
conducted for (1) line to load terminals with CB open, (2) line to
line terminals with CB closed, and (3) pole to ground with CB open,
and (4) pole to ground with CB closed.
. Attachment 2
NRCB 88-10
November 22, 1988
DEFINITION OF TERMS
CIRCUIT BREAKER MANUFACTURER (CBM)
The manufacturing facility that actually produced the circuit breaker being
purchased.
VERIFIABLE TRACEABILITY
Documented evidence such as a certificate of compliance that establishes
traceability of purchased equipment to the CBM. If the certificate of
compliance is provided by any party other than the CBM, the validity of such
certificate must be verified by the licensee or permit holder through an audit
or other appropriate means.
DEDICATION PROCESS
The process by which commercial grade (non-Class 1E) equipment is upgraded to
safety-related (Class 1E) and is thereby considered qualified for use in
safety-related applications. The dedication process must include:
a. A technical evaluation to determine the characteristics critical
to fulfilling the safety function(s).
b. An acceptance process to ensure that those critical characteristics
are met.
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021