[Circuit Breakers] Circuit Breakers, Molded-case and Circuit Breaker Enclosures
Guide Information
USE
This category covers circuit breakers and circuit breaker enclosures designed to provide service-entrance, feeder or branch circuit protection in accordance with ANSI/NFPA 70, "National Electrical Code" (NEC).
These circuit breakers are intended for use with Listed enclosures, or as part of other Listed equipment, or without enclosures where acceptable.
Investigation of a Listed "replacement circuit breaker" involves only the circuit breaker and associated parts; the end application or any series combination application has not been investigated.
Some circuit breakers are not provided with a means to prevent their installation in Class CTL assemblies. These circuit breakers are for use in old style, non-Class CTL equipment and are marked "For Replacement Use Only, Not CTL Assemblies."
Circuit breakers marked "SWD" and rated 347 V or less are suitable for switching fluorescent lighting loads on a regular basis at their rated voltage.
Circuit breakers marked "HID" have been investigated for switching high-intensity discharge lighting loads on a regular basis at their rated voltage.
Some circuit breakers include a pole intended to disconnect the grounded circuit conductor of a branch circuit. All poles of these circuit breakers open simultaneously.
Single-pole circuit breakers rated 120 V ac are suitable for use on circuits rated 120 V to ground.
Single-pole or multi-pole independent trip circuit breakers, with or without handle ties, rated 120/240 V ac, are suitable for use in a single-phase, multi-wire circuit on line-to-neutral connected loads.
Single-pole or multi-pole independent trip circuit breakers, with handle ties, rated 120/240 V ac, are suitable for use on multi-wire circuits with line-to-line or line-to-ground connected loads.
2-pole independent trip breakers and single-pole breakers with handle ties, rated 120/240 V ac, are suitable for use in line-to-line single-phase circuits or line-to-line lighting and appliance branch circuits connected to 3-phase, 4-wire systems, provided the systems have a grounded neutral and the voltage to ground does not exceed 120 V.
2-pole independent trip breakers and single-pole breakers with handle ties, rated 125/250 V dc, are suitable for use in line-to-line connected 3-wire dc circuits supplied from a system with a grounded neutral where the voltage to ground does not exceed 125 V.
2-pole independent trip breakers and single-pole breakers with handle ties, rated 125/250 V (both ac and dc), are suitable for use in accordance with either of the above two paragraphs, as applicable.
Some independent trip circuit breakers are marked "independent trip,""no common trip" or equivalent wording.
3-pole circuit breakers having provision for two poles to be connected to a bus structure and a third isolated pole (commonly referred to as delta breakers) are marked "For Replacement Use Only."
3-pole circuit breakers are suitable for use only on 3-phase systems unless marked to indicate otherwise.
Multi-pole common trip circuit breakers rated 120/240 V ac are suitable for use in a single-phase multi-wire circuit, with or without the neutral connected to the load, where the voltage to ground does not exceed 120 V.
Multi-pole common trip circuit breakers rated 125/250 V or 125/250 V dc are suitable for use in a single-phase and a dc multi-wire circuit, with or without the neutral connected to the load, where the voltage to ground does not exceed 125 V.
Circuit breakers, the performance of which may be affected by a 40?C ambient temperature within the enclosure, and that have been investigated for this application, are marked "40 C."
Unless otherwise marked, circuit breakers should not be loaded to exceed 80 percent of their current rating, where in normal operation the load will continue for three hours or more.
Circuit breakers rated 50 A or less and 125/250 V or less are investigated for use with tungsten-filament lamp loads.
Circuit breaker enclosures marked for service equipment use may also be used to provide the main control and means of cutoff for a separately derived system or a second building.
Circuit breaker enclosures identified with an enclosure type designation are intended for use as indicated in Electrical Equipment for Use in Ordinary Locations (AALZ).
A current-limiting circuit breaker is one that does not employ a fusible element and that when operating within its current-limiting range, limits the let-through I2t to a value less than the I2t of a 1/2 cycle wave of the symmetrical prospective current.
PRODUCT TYPES
Circuit breakers and circuit breaker enclosures are indicated by the label designations as follows:
Circuit Breaker ? without enclosure, and with noninterchangeable trip units.
CTL Circuit Breaker ? has physical size, configuration or other means which, in conjunction with the physical means provided in a Class CTL assembly, is designed to prevent the installation of more circuit breaker poles than the number for which the assembly is designed and rated.
Circuit Breaker Frame ? frame only of circuit breaker with provision for interchangeable trip units. A labeled circuit breaker frame is Listed for use only with a labeled circuit breaker trip unit.
Circuit Breaker Trip Unit ? trip unit only of circuit breaker having provision for interchangeable trip units.
Circuit Breaker Enclosure ? enclosure only for individual 1-, 2- or 3-pole circuit breaker or for two single-pole breakers not interconnected.
Replacement Circuit Breaker ? a present design with external modifications to permit its mounting in place of obsolete designs of the same manufacturer in previously Listed applications, such as panelboards, switchboards and the like, which are still in service.
INSTALLATION
Some circuit breakers include a ground-fault trip element. These ground-fault trip elements have been investigated in accordance with UL 1053, "Ground-Fault Sensing and Relaying Equipment," and are suitable for providing ground-fault protection of equipment in accordance with Sections 215.10, 230.95 or 240.13 of the NEC.
Circuit breakers with ground-fault elements intended for use in accordance with NEC Articles 426 or 427 are covered under Circuit Breakers with Equipment Ground Fault Protection (DIYA).
Circuit breakers are tested under overload conditions at six times the rating to cover motor circuit applications and are suitable for use as motor circuit disconnects per Section 430.109 of the NEC.
Listed circuit breakers may be mounted in any position unless marked to indicate otherwise. If, however, the circuit breaker is mounted so that the handle is operated vertically rather than rotationally or horizontally, the up position of the handle should be in the "on" position.
Line and load markings on a circuit breaker are intended to limit connections thereto as marked.
RATINGS
Listed circuit breakers are rated 600 V or less. A circuit breaker is marked AC or DC or both AC and DC. A symbol (~), where used, represents AC. The frequency is included if other than 60 Hz.
Circuit breakers that have an interrupting rating higher than 5000 A are marked to indicate the higher rating(s).
An interrupting rating on a circuit breaker included in a piece of equipment does not automatically qualify the equipment in which the circuit breaker is installed for use on circuits with higher available currents than the rating of the equipment itself.
Circuit breaker enclosures that have a short-circuit current rating are marked accordingly.
PRODUCT MARKINGS
A circuit breaker that includes an accessory device, whether attached to the circuit breaker by the manufacturer of the circuit breaker, or by others, is marked to indicate the presence of that accessory.
Where the accessory is a shunt trip device that is suitable for operation with ground-fault sensing and relaying equipment, such suitability is indicated in the marking of the circuit breaker.
2-pole circuit breakers suitable for controlling 3-phase, corner-grounded delta circuits are marked to indicate their suitability.
Circuit breaker enclosures that are suitable for use as service equipment are marked accordingly.
Some circuit breakers are intended to be used with uninterruptible power supplies (UPS) with two or three poles connected in series. These circuit breakers are marked with both the maximum and nominal DC voltage of the system where use is intended, a wiring diagram showing the proper connections of the poles in series, and a statement that these DC ratings are applicable only with UPS.
Circuit breakers investigated for use with heating, air conditioning and refrigeration equipment comprising multi-motor or combination loads are marked "HACR TYPE," in conjunction with the Listing Mark. Such circuit breakers are suitable for use with heating, air conditioning and refrigerating equipment marked for use with HACR type circuit breakers. Use of these circuit breakers with heating, air conditioning and refrigerating equipment is limited to installations where the equipment is marked as suitable for use with any properly sized circuit breaker, or is marked for use with a HACR type circuit breaker, or is not limited by any marking as to the type of branch circuit, short-circuit and ground-fault protective device.
Current-limiting circuit breakers are marked "current limiting" and are marked either to indicate the let-through characteristics or to indicate where such information may be obtained.
Circuit breakers investigated for application aboard noncombatant and auxiliary naval ships are marked "Naval." The Marine Listing Mark identifies circuit breakers investigated for use in a marine environment. For additional information on circuit breakers suitable for naval and marine use, see Circuit Breakers, Molded-case and Circuit Breaker Enclosures, Marine (DKTY).
ADDITIONAL INFORMATION
For additional information, see Circuit Breakers (DHJR) and Electrical Equipment for Use in Ordinary Locations (AALZ).
REQUIREMENTS
The basic standard used to investigate products in this category is UL 489, "Molded-Case Circuit Breakers, Molded-Case Switches and Circuit Breaker Enclosures."
UL MARK
The Listing Mark of Underwriters Laboratories Inc. on the product is the only method provided by UL to identify products manufactured under its Listing and Follow-Up Service. The Listing Mark for these products includes the UL symbol (as illustrated in the Introduction of this Directory) together with the word "LISTED," a control number, and one of the following product names, as appropriate: "Circuit Breaker,""CTL Circuit Breaker,""Circuit Breaker Frame,""Circuit Breaker Trip Unit,""Circuit Breaker Enclosure" or "Replacement Circuit Breaker." The words "Circuit Breaker" may be abbreviated "C.B." in all of the product names permitted above (e.g., "C.B. Enclosure").
The Marine Listing Mark identifies circuit breakers investigated for use in a marine environment.
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