MIL-DTL-17361G(SH)
APPENDIX A
AQB/NQB CIRCUIT BREAKER OBSOLESCENCE AND RELATED INFORMATION
A.1. SCOPE
A.1.1 Scope. This Appendix is not a mandatory part of the specification. The information contained
herein is intended for guidance only. MIL-DTL-17361G covers different types of AQB/NQB thermal magnetic
and electronic circuit breakers. At present, there are only two AQB/NQB circuit breaker vendors, SPD
Technologies and Cutler-Hammer (formerly Westinghouse). SPD has made their entire line of thermal magnetic
circuit breakers obsolete but continues to manufacture electronic circuit breakers. Cutler-Hammer continues to
manufacture a mixture of thermal magnetic and electronic circuit breakers. With obsolescence, there is a chance
that a particular SPD thermal magnetic circuit breaker may not be available to use as a replacement for a failed
circuit breaker in the field. This appendix provides replacement information to users so that they can make
informed decisions if the need arises. Note the following:
a. Electronic circuit breakers are available as replacements for most applications and in some instances may
be the only replacement option. Cutler-Hammer may also have a form, fit, and function thermal magnetic circuit
breaker as a replacement option depending on the frame size. Sections 2 and 3 of this appendix provide general and
detailed information on each circuit breaker frame size for both vendors.
b. To properly assess alternative circuit breakers as possible functional replacements for obsolete circuit
breakers, users need to be aware of similarities and differences in attachments (motor operators, undervoltage
releases, shunt trips, auxiliary contacts) between SPD and Cutler-Hammer circuit breakers as well as between
thermal magnetic and electronic circuit breakers from the same vendor. Section 3 and Tables A-I through A-VI of
this appendix provide attachment information.
c. An electronic AQB circuit breaker has several more adjustable settings than a thermal magnetic circuit
breaker. Users need guidance on how to set the electronic circuit breaker to ensure that, with regard to
instantaneous protection, it is a functional equivalent for the thermal magnetic circuit breaker being replaced.
Section A.3.8 and Tables A-VI through A-XVIII of this appendix provide such guidance.
It should not be construed that the nature of the information in this appendix precludes other vendors from
qualifying AQB circuit breakers. There are only two manufacturers at present and that fact determines the
information currently provided. If another manufacturer qualifies a circuit breaker(s), that circuit breaker(s)
information will be included in this appendix for the next revision.
A.2. GENERAL CIRCUIT BREAKER INFORMATION
A.2.1 SPD AQB/NQB circuit breakers.
A.2.1.1 Obsolete thermal magnetic. The following circuit breakers are obsolete:
AQB-A50 and NQB-A50
AQB-A100 and NQB-A100
AQB-LF100
AQB-A101 and NQB-A101
AQB-A250 and NQB-A250
AQB-LF226
AQB-LF250
AQB-A400 and NQB-A400
AQB-LF400
AQB-A800 and NQB-A800
AQB-A1600 and NQB-A1600
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