The standards that are applicable to low voltage power circuit breakers and the testing involved to prove compliance by a specific low voltage power circuit breaker design are in Module 5 and previously in this module. You learned from those discussions that standards and testing go to the heart of the matter. This is true from three very important standpoints:
1. This is the industry's determination as to whether or not a particular circuit breaker design is capable of meeting a wide range of published operational and physical requirements.
2. The proven and stated compliance to specific standards tells potential users that the equipment from the manufacturers under consideration all meet certain basic standards, which makes the user's evaluation process much simpler. Once this determination is made, a particular manufacturer can still gain an evaluated advantage by offering additional unique features and/or an operational design approach preferred by the user.
3. It is a solid way of defining specific types of circuit breakers within a larger general grouping. For example: The larger general grouping is "Low Voltage Circuit Breakers." Specific types within the Low Voltage Circuit Breaker grouping would be "Low Voltage Power, Insulated Case, Molded Case and Miniature."
As you can see, when a specific type circuit breaker is specified, such as a low voltage power circuit breaker, the specifier already knows what the base expectations are from each manufacturer.
You will recall, from both Module 5 and previous sections, a map of the world showing the standards most influential in different parts of the world (Figure 37). It bears revisiting the map again to emphasize the importance, in today's global economy, of having flexible designs capable of complying with all major standards around the world. In this module the emphasis will be primarily on ANSI and IEC Standards. You should never lose sight of the fact, however, that there are a number of other standards that can play a critical role in determining what equipment is acceptable for application in a given area of the world. Even local and/or individual city codes and requirements may have to be considered.
In previous modules, references other than ANSI and IEC were made with respect to standards and testing, such as UL, IEEE. There is a strong relationship between ANSI, UL and IEEE. As a matter of fact, you will notice in manufacturer's publications for low voltage power circuit breakers and even low voltage metal enclosed switchgear references made to all. The following two samples are typical statements you might encounter when reading publications for both the power circuit breaker and the metal enclosed switchgear:
Typical Low Voltage Power Circuit Breaker Statement: "Type XYZ low voltage power circuit breakers are UL listed, and built and tested to applicable NEMA, ANSI, IEEE and UL standards (ANSI C37.50, C37.13, UL 1066)."
Typical Low Voltage Metal Enclosed Switchgear Statement: "Type XYZ low voltage metal enclosed switchgear conforms to NEMA SG3, NEMA SG5, ANSI C37.20.1, ANSI C37.51 and UL1558."
It may seem to you like a confusing web at this point. Once the relationship is understood, it will be clear as to why these references are made. There will be no detailed discussion of the standards relating to low voltage metal enclosed in this module, only those relevant to the power circuit breaker. Keep in mind, however, it works the same way. The standards state different requirements for the different pieces of equipment, but the intent is the same - an uncompromised piece of equipment with proven performance capabilities.
For the purpose of this section, let's identify the key players as a minimum and elaborate on a couple. This should not be considered as a substitute for the standards themselves. For a full explanation of any standard, consult the standard itself for details and proper conformance instructions.
IEEE (Institute of Electrical and Electronic Engineers)
• IEEE is an objective technical organization made up of manufacturers, users, and other general interest parties.
• IEEE defines technical definitions, technical requirements, temperature limits, altitude correction, insulation limits, and service conditions. For electrical equipment, including switchgear, it supplies the test requirements for the low voltage power circuit breaker construction and test standards, namely ANSI C37.13 and ANSI C37.50.
NEMA (National Electrical Manufacturers Association)
• NEMA is an electrical equipment manufacturer only organization, such as Cutler-Hammer, General Electric, and Square D. NEMA defines preferred ratings, related requirements, and application recommendations.
• NEMA Standards normally cover additional information about a product of specific interest to the manufacturing community, which the American National Standards Committee does not include in its scope. NEMA votes on the suitability of standards for ANSI designation and adopts, by reference, the appropriate American National Standards.
• The applicable low voltage power circuit breaker NEMA Standard is SG-3, and it adopts ANSI C37.16 in its entirety.
UL (Underwriters Laboratories Inc.)
• UL is an independent, non profit, third party testing and certification company headquartered in Northbrook, Illinois. It functions to develop standards and to insure that equipment meets relevant published standards.
• UL also adopts otherwise recognized standards, and, in some instances, develops their own independent certification tests. In the case of low voltage power circuit breakers, the UL Standard is UL1066, which was previously mentioned. UL1066, entitled "Standard for Low Voltage AC and DC Power Circuit Breakers Used in Enclosures," calls for testing to demonstrate compliance with ANSI/IEEE C37.13 without change. A UL Label is affixed to the circuit breaker to indicate successful compliance.
CSA (Canadian Standards Association)
• The Canadian Standards Association is in the category of a major international standard. Its design and testing requirements are essentially the same as required by UL. In fact, harmonization programs between UL and CSA are ongoing to close the gap and/or eliminate differences. The Canadian Standards Association standard most associated with low voltage power circuit breakers is CSA 22.2-31 for Switchgear Assemblies.
ANSI (American National Standards Institute)
You were briefly introduced to ANSI. Now let's take the time to get to know ANSI much better because ANSI is the key to low voltage power circuit breakers. It is the recognized North American Authority on equipment standards.
ANSI's Purpose - ANSI is a nonprofit, privately-funded membership organization that coordinates the development of U.S. voluntary national standards, called American National Standards. It is also the U.S. member body to the non-treaty international standards bodies, such as the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). ANSI serves both the private and public sectors' need for voluntary standardization.
ANSI's History - The institute was founded in 1918. It was prompted by the need for an umbrella organization to coordinate the activities of the U.S. voluntary standards system and eliminate conflict and/or duplication in the development process. The institute serves a diverse membership of over 1300 companies, 250 professional, technical, trade, labor and consumer organizations, and some 30 government agencies.
A simple yet very typical example of why ANSI came into existence can be related to the low voltage power circuit breaker. In the early days of low voltage power circuit breaker development, manufacturers and users were building and applying equipment with little thought given to uniform performance or design standardization. The C37 standard was developed and implemented to establish minimum performance standards for the circuit breaker and its physical design features.
The standard was meant to address even the smallest detail. A close button, for example, might not say close on it or it varied in color from one manufacturer to the next. These inconsistencies in design made products confusing for use by customers. This might seem to be one trivial point, but you can imagine how big the problem would be when compounded with every aspect of a low voltage power circuit breaker.
ANSI's Functions - ANSI functions to:
• Coordinate the self-regulating, due process consensus voluntary standards system
• Administer the development of standards and approve them as American National Standards
• Provide the means for the U.S. to influence development of international and regional standards
• Disseminate timely and important information on national, international and regional standards activities to U.S. industry
These standards are intended to provide guidance, direction, and requirements. Compliance to these standards does not, nor is it meant to limit manufacturers in construction, materials, or the technology used.
Specifically relating to power circuit breakers, ANSI standards are written by either the IEEE Switchgear Committee or NEMA. The electrical standards written by both of these organizations are reviewed and clarified by the Accredited Standards Committee (ASC) for power switchgear and power circuit breakers. The ASC standards group is entitled C37.
ANSI Defined Standards for Low Voltage Power Circuit Breakers - Although there are a multitude of ANSI standards relating to many different types of equipment, only those standards relating to low voltage power circuit breakers are outlined here. The intent is just to make you aware of just how many are applicable to just one category of electrical equipment. You will notice that each standard is followed by a specific year. As additions or changes are made to a standard, the year is altered to indicate the latest version. Obviously, staying on top of the latest version is an ongoing process. You should also note that each standard is given a broad word definition.
1. ANSI/IEEE C37.13-1990, "Low Voltage AC Power Circuit Breakers Used in Enclosures"
2. ANSI C37.16-1997, "Preferred Ratings Related Requirements and Application Recommendations for Low Voltage Power Circuit Breakers and AC Power Circuit Protectors"
3. ANSI C37.17-1997, "Trip Devices for AC and General Purpose DC Low Voltage Power Circuit Breakers"
4. ANSI C37.50-1989, "Test Procedures for Low Voltage AC Power Circuit Breakers Used in Enclosures"
5. IEEE Standard C37.100-1992, "IEEE Standard Definitions for Power Switchgear"
6. IEEE C37.20.1-1993, "Standard for Metal-Enclosed Low Voltage Power Circuit Breaker Switchgear"
7. ANSI C37.51-1989, "Standard for Switchgear - Metal-Enclosed Low Voltage AC Power Circuit Breaker Switchgear Assemblies - Conformance Test Procedures"
8. NEMA SG-3-1981, "Low Voltage Power Circuit Breakers"
9. UL1066-1993, "Standard for Low Voltage AC and DC Power Circuit Breakers Used in Enclosures"
This lengthy list gives you some indication why it is a matter of practicality when a manufacturer states that a piece of equipment is built and tested to all applicable NEMA, ANSI, IEEE and UL standards. It was also mentioned that a great deal of referencing to other standards takes place within the body of a specific standard. Successful testing and compliance with respect to one standard often includes automatic compliance with other standards. It is worth repeating one of the examples given.
Example: ANSI C37.13 details the physical attributes, such as Stored Energy, that a low voltage AC power circuit breaker must have to comply. At the same time, ANSI C37.50 references C37.13 and details how the described circuit breaker should be tested. The key here is that successful testing in keeping with ANSI C37.50 brings with it compliance to C37.13. There is no need to mention C37.13, when it is stated that the circuit breaker complies with C37.50.
IEC (International Electrotechnical Commission)
IEC presides over the standardization of equipment for a number of other parts of the world. In view of today's global markets, there is a significant amount of interaction between the organizations just discussed and IEC.
IEC 947-2 is a multi-part international testing standard covering a variety of devices, including circuit breakers of all types. It is entitled "Low Voltage Switchgear and Controlgear."
As far as IEC is concerned, every device tested to IEC 947-2 must be subjected to several test sequences in order to be approved. Because IEC 947-2 covers both low voltage power circuit breakers and low voltage molded case circuit breakers, the exact test sequences performed are not necessarily the same. They depend on the category of the device.
Category A Device - In general, this is a device without a short time Withstand Rating, such as a molded case circuit breaker.
Category B Device - This is a device with a short time withstand rating, such as a power circuit breaker and certain molded case circuit breakers. Typically, these devices are referred to as Air Circuit Breakers or just ACBs.
IEC 947-2 was developed with assistance from members of the U.S. National Committee. Still, a number of significant differences exist between IEC 947-2 and applicable ANSI standards. In particular, the various ratings of a circuit breaker can differ when tested to each standard. Therefore, any product comparisons made between products tested to these different standards (domestic versus international) should only be made with a thorough understanding of the differences.
Standards Conclusion
This might seem to be a monumental amount of information about standards. It is only the tip of the iceberg. This is not to imply that you must be an expert on standards to deal with power circuit breakers. You can, however, begin to appreciate just how much effort, investment, and plain hard work goes into being able to legitimately print in a document a statement such as:
"Magnum DS Low Voltage Power Circuit Breakers are UL Listed and built and tested to all applicable ANSI Standards." Keep in mind that all these standards establish minimum requirements. There is nothing prohibiting a manufacturer from exceeding standards by offering additional features and/or using newer and improved operational techniques for more efficient and higher levels of performance. Magnum DS does just that in a number of areas.
The majority of the remaining discussions in this module will be presented as they relate to applicable ANSI Standards. Remember, however, that other standards do exist in other parts of the world. They must be complied with to participate in the international segment (Figure 38).
Figure 38. Circuit Breaker Identification
Low Voltage Power Circuit Breaker C37.50 Testing
Testing of a low voltage power circuit breaker in keeping with required ANSI Standards provides the first glimpse at what makes a low voltage power circuit breaker unique. Remember, low voltage power circuit breakers are applied at or below their nameplate ratings. That nameplate rating is a result of having successfully completed a series of rigorous tests. This is referred to as a 100% rating.
Although every detail of the testing will not be covered here, you will have an appreciation for just how demanding these ANSI defined tests are for low voltage power circuit breakers. The tests will be described as four test sequences. It should be pointed out here that all tests are performed using a Drawout circuit breaker in its enclosure for each frame size.
The first three test sequences are similar in many ways to the tests performed on other types of low voltage circuit breakers, such as a molded case circuit breaker. It is the fourth test sequence performed on a low voltage power circuit breaker that differentiates the power circuit breaker from other types of circuit breakers.
Note that all the following test sequences, except for Test Sequence 4 in which the circuit breaker has no Trip Unit, are preceded and followed by a calibration test and dielectric check.
Test Sequence 1 - This test sequence consists of a temperature rise test, an overload switching test, and then a short circuit test. The circuit breaker is equipped with an instantaneous trip.
1. The circuit breaker is loaded to 100% of the maximum rating of the frame size (in normal enclosure) until the temperature is constant. The standard lists the maximum permissible temperature rises at various parts of the circuit breaker.
2. The circuit breaker is then subjected to number of opening operations on over-load switching.
3. The circuit breaker is then given a 3-phase short circuit test at its maximum voltage rating, which is 635 volts for this 600 volt rated circuit breaker. The short circuit current in this case can be no less than the 600 volt interrupting capacity of the circuit breaker being tested. The three maximum voltages used during testing and typically listed on the nameplate are listed below along with their corresponding application voltages:
Maximum Voltage Application Voltage
635 volts 600 volts
508 volts 480 volts
254 volts 240 volts
4. The short circuit test consists of initiating current through the closed circuit breaker, causing it to trip. After 15 seconds, the circuit breaker is re-closed on the fault, and then allowed to trip open to clear the fault. This is known as an O-CO (open-close open) test.
5. The short circuit test is followed by a calibration check and a dielectric test.
Test Sequence 2 - This test sequence consists of a series of short circuit tests on a circuit breaker equipped with selective tripping (no instantaneous).
1. Once again, all short circuit tests are preceded by a dielectric test and a calibration test. After the interruptions, the circuit breaker is given another dielectric test and the calibration is again checked.
2. Each short circuit test is an O-CO test meaning that the circuit breaker interrupts the full fault current twice.
3. After the 3-phase short circuit tests are completed at different prescribed voltages, single phase tests are performed. A new circuit breaker may be used for each test, or each test may be done on different poles of the same circuit breaker.
4. One single-phase test is done at each of the same three maximum voltage ratings used for the three-phase tests (635, 508 and 254 volts) at the appropriate Interrupting Rating for that voltage.
Test Sequence 3 - This test sequence includes tests of mechanical and electrical endurance.
1. A circuit breaker is calibrated, given a dielectric test, and subjected to a large number of operations. Some of the operations are at no load and some at full load.
2. The required number of operations varies by circuit breaker frame size.
3. After the endurance test, the same circuit breaker is given a full 3-phase O-CO short circuit test at 635 volts and a dielectric withstand test.
The required number of operations for the endurance test just described is about the same for larger frame power circuit breakers and somewhat higher for smaller frame power circuit breakers compared to molded case circuit breaker endurance tests. For the sake of comparison, refer to the two endurance ratings tables, one for power circuit breakers and one for molded case circuit breakers .
Test Sequence 4 - This test sequence includes a short time current (withstand) test. Molded case and insulated case circuit breakers are not usually subjected to this type of test and, therefore, have no full 30 cycle Short Time Rating. This is one of the key differences.
1. For this test, the circuit breaker does not have a trip unit or the trip unit is disconnected. During the short-circuit testing, the circuit breaker can be tripped instantaneously by a shunt trip.
2. The circuit breaker is closed and then energized at its full short time current rating. The short time rating is usually equal to the 600 volt short circuit current rating.
3. The current is left on for 30 cycles (1/2 second), then off for 15 seconds, then back on for another 30 cycles. The circuit breaker remains closed during this test sequence.
4. After the short time current (withstand) tests, the same circuit breaker is given a 3-phase short circuit test sequence at full short circuit current rating and 635 volts. The circuit breaker is opened as quickly as possible by the shunt trip, which is energized at the same instant the power is applied. The intent is to force the circuit breaker to open during the worst case conditions (full current asymmetry). This is where the short time rating for the circuit breaker comes from.
5. After the final test, the circuit breaker calibration is checked and given a dielectric withstand test.
During Test Sequence 4, the circuit breaker is subjected to tremendous physical forces from the magnetic fields and to severe heating effects from the current. Think about it. Both the magnetic forces and the heating vary with the square of the current (Figure 41). For example, a 4000 ampere frame low voltage power circuit breaker at 85,000 amperes is subjected to forces and heating more than 450 times normal for each 30 cycle test. It is quite awesome.
Labels:
Circuit Breaker
1. This is the industry's determination as to whether or not a particular circuit breaker design is capable of meeting a wide range of published operational and physical requirements.
2. The proven and stated compliance to specific standards tells potential users that the equipment from the manufacturers under consideration all meet certain basic standards, which makes the user's evaluation process much simpler. Once this determination is made, a particular manufacturer can still gain an evaluated advantage by offering additional unique features and/or an operational design approach preferred by the user.
3. It is a solid way of defining specific types of circuit breakers within a larger general grouping. For example: The larger general grouping is "Low Voltage Circuit Breakers." Specific types within the Low Voltage Circuit Breaker grouping would be "Low Voltage Power, Insulated Case, Molded Case and Miniature."
As you can see, when a specific type circuit breaker is specified, such as a low voltage power circuit breaker, the specifier already knows what the base expectations are from each manufacturer.
You will recall, from both Module 5 and previous sections, a map of the world showing the standards most influential in different parts of the world (Figure 37). It bears revisiting the map again to emphasize the importance, in today's global economy, of having flexible designs capable of complying with all major standards around the world. In this module the emphasis will be primarily on ANSI and IEC Standards. You should never lose sight of the fact, however, that there are a number of other standards that can play a critical role in determining what equipment is acceptable for application in a given area of the world. Even local and/or individual city codes and requirements may have to be considered.
In previous modules, references other than ANSI and IEC were made with respect to standards and testing, such as UL, IEEE. There is a strong relationship between ANSI, UL and IEEE. As a matter of fact, you will notice in manufacturer's publications for low voltage power circuit breakers and even low voltage metal enclosed switchgear references made to all. The following two samples are typical statements you might encounter when reading publications for both the power circuit breaker and the metal enclosed switchgear:
Typical Low Voltage Power Circuit Breaker Statement: "Type XYZ low voltage power circuit breakers are UL listed, and built and tested to applicable NEMA, ANSI, IEEE and UL standards (ANSI C37.50, C37.13, UL 1066)."
Typical Low Voltage Metal Enclosed Switchgear Statement: "Type XYZ low voltage metal enclosed switchgear conforms to NEMA SG3, NEMA SG5, ANSI C37.20.1, ANSI C37.51 and UL1558."
It may seem to you like a confusing web at this point. Once the relationship is understood, it will be clear as to why these references are made. There will be no detailed discussion of the standards relating to low voltage metal enclosed in this module, only those relevant to the power circuit breaker. Keep in mind, however, it works the same way. The standards state different requirements for the different pieces of equipment, but the intent is the same - an uncompromised piece of equipment with proven performance capabilities.
For the purpose of this section, let's identify the key players as a minimum and elaborate on a couple. This should not be considered as a substitute for the standards themselves. For a full explanation of any standard, consult the standard itself for details and proper conformance instructions.
IEEE (Institute of Electrical and Electronic Engineers)
• IEEE is an objective technical organization made up of manufacturers, users, and other general interest parties.
• IEEE defines technical definitions, technical requirements, temperature limits, altitude correction, insulation limits, and service conditions. For electrical equipment, including switchgear, it supplies the test requirements for the low voltage power circuit breaker construction and test standards, namely ANSI C37.13 and ANSI C37.50.
NEMA (National Electrical Manufacturers Association)
• NEMA is an electrical equipment manufacturer only organization, such as Cutler-Hammer, General Electric, and Square D. NEMA defines preferred ratings, related requirements, and application recommendations.
• NEMA Standards normally cover additional information about a product of specific interest to the manufacturing community, which the American National Standards Committee does not include in its scope. NEMA votes on the suitability of standards for ANSI designation and adopts, by reference, the appropriate American National Standards.
• The applicable low voltage power circuit breaker NEMA Standard is SG-3, and it adopts ANSI C37.16 in its entirety.
UL (Underwriters Laboratories Inc.)
• UL is an independent, non profit, third party testing and certification company headquartered in Northbrook, Illinois. It functions to develop standards and to insure that equipment meets relevant published standards.
• UL also adopts otherwise recognized standards, and, in some instances, develops their own independent certification tests. In the case of low voltage power circuit breakers, the UL Standard is UL1066, which was previously mentioned. UL1066, entitled "Standard for Low Voltage AC and DC Power Circuit Breakers Used in Enclosures," calls for testing to demonstrate compliance with ANSI/IEEE C37.13 without change. A UL Label is affixed to the circuit breaker to indicate successful compliance.
CSA (Canadian Standards Association)
• The Canadian Standards Association is in the category of a major international standard. Its design and testing requirements are essentially the same as required by UL. In fact, harmonization programs between UL and CSA are ongoing to close the gap and/or eliminate differences. The Canadian Standards Association standard most associated with low voltage power circuit breakers is CSA 22.2-31 for Switchgear Assemblies.
ANSI (American National Standards Institute)
You were briefly introduced to ANSI. Now let's take the time to get to know ANSI much better because ANSI is the key to low voltage power circuit breakers. It is the recognized North American Authority on equipment standards.
ANSI's Purpose - ANSI is a nonprofit, privately-funded membership organization that coordinates the development of U.S. voluntary national standards, called American National Standards. It is also the U.S. member body to the non-treaty international standards bodies, such as the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). ANSI serves both the private and public sectors' need for voluntary standardization.
ANSI's History - The institute was founded in 1918. It was prompted by the need for an umbrella organization to coordinate the activities of the U.S. voluntary standards system and eliminate conflict and/or duplication in the development process. The institute serves a diverse membership of over 1300 companies, 250 professional, technical, trade, labor and consumer organizations, and some 30 government agencies.
A simple yet very typical example of why ANSI came into existence can be related to the low voltage power circuit breaker. In the early days of low voltage power circuit breaker development, manufacturers and users were building and applying equipment with little thought given to uniform performance or design standardization. The C37 standard was developed and implemented to establish minimum performance standards for the circuit breaker and its physical design features.
The standard was meant to address even the smallest detail. A close button, for example, might not say close on it or it varied in color from one manufacturer to the next. These inconsistencies in design made products confusing for use by customers. This might seem to be one trivial point, but you can imagine how big the problem would be when compounded with every aspect of a low voltage power circuit breaker.
ANSI's Functions - ANSI functions to:
• Coordinate the self-regulating, due process consensus voluntary standards system
• Administer the development of standards and approve them as American National Standards
• Provide the means for the U.S. to influence development of international and regional standards
• Disseminate timely and important information on national, international and regional standards activities to U.S. industry
These standards are intended to provide guidance, direction, and requirements. Compliance to these standards does not, nor is it meant to limit manufacturers in construction, materials, or the technology used.
Specifically relating to power circuit breakers, ANSI standards are written by either the IEEE Switchgear Committee or NEMA. The electrical standards written by both of these organizations are reviewed and clarified by the Accredited Standards Committee (ASC) for power switchgear and power circuit breakers. The ASC standards group is entitled C37.
ANSI Defined Standards for Low Voltage Power Circuit Breakers - Although there are a multitude of ANSI standards relating to many different types of equipment, only those standards relating to low voltage power circuit breakers are outlined here. The intent is just to make you aware of just how many are applicable to just one category of electrical equipment. You will notice that each standard is followed by a specific year. As additions or changes are made to a standard, the year is altered to indicate the latest version. Obviously, staying on top of the latest version is an ongoing process. You should also note that each standard is given a broad word definition.
1. ANSI/IEEE C37.13-1990, "Low Voltage AC Power Circuit Breakers Used in Enclosures"
2. ANSI C37.16-1997, "Preferred Ratings Related Requirements and Application Recommendations for Low Voltage Power Circuit Breakers and AC Power Circuit Protectors"
3. ANSI C37.17-1997, "Trip Devices for AC and General Purpose DC Low Voltage Power Circuit Breakers"
4. ANSI C37.50-1989, "Test Procedures for Low Voltage AC Power Circuit Breakers Used in Enclosures"
5. IEEE Standard C37.100-1992, "IEEE Standard Definitions for Power Switchgear"
6. IEEE C37.20.1-1993, "Standard for Metal-Enclosed Low Voltage Power Circuit Breaker Switchgear"
7. ANSI C37.51-1989, "Standard for Switchgear - Metal-Enclosed Low Voltage AC Power Circuit Breaker Switchgear Assemblies - Conformance Test Procedures"
8. NEMA SG-3-1981, "Low Voltage Power Circuit Breakers"
9. UL1066-1993, "Standard for Low Voltage AC and DC Power Circuit Breakers Used in Enclosures"
This lengthy list gives you some indication why it is a matter of practicality when a manufacturer states that a piece of equipment is built and tested to all applicable NEMA, ANSI, IEEE and UL standards. It was also mentioned that a great deal of referencing to other standards takes place within the body of a specific standard. Successful testing and compliance with respect to one standard often includes automatic compliance with other standards. It is worth repeating one of the examples given.
Example: ANSI C37.13 details the physical attributes, such as Stored Energy, that a low voltage AC power circuit breaker must have to comply. At the same time, ANSI C37.50 references C37.13 and details how the described circuit breaker should be tested. The key here is that successful testing in keeping with ANSI C37.50 brings with it compliance to C37.13. There is no need to mention C37.13, when it is stated that the circuit breaker complies with C37.50.
IEC (International Electrotechnical Commission)
IEC presides over the standardization of equipment for a number of other parts of the world. In view of today's global markets, there is a significant amount of interaction between the organizations just discussed and IEC.
IEC 947-2 is a multi-part international testing standard covering a variety of devices, including circuit breakers of all types. It is entitled "Low Voltage Switchgear and Controlgear."
As far as IEC is concerned, every device tested to IEC 947-2 must be subjected to several test sequences in order to be approved. Because IEC 947-2 covers both low voltage power circuit breakers and low voltage molded case circuit breakers, the exact test sequences performed are not necessarily the same. They depend on the category of the device.
Category A Device - In general, this is a device without a short time Withstand Rating, such as a molded case circuit breaker.
Category B Device - This is a device with a short time withstand rating, such as a power circuit breaker and certain molded case circuit breakers. Typically, these devices are referred to as Air Circuit Breakers or just ACBs.
IEC 947-2 was developed with assistance from members of the U.S. National Committee. Still, a number of significant differences exist between IEC 947-2 and applicable ANSI standards. In particular, the various ratings of a circuit breaker can differ when tested to each standard. Therefore, any product comparisons made between products tested to these different standards (domestic versus international) should only be made with a thorough understanding of the differences.
Standards Conclusion
This might seem to be a monumental amount of information about standards. It is only the tip of the iceberg. This is not to imply that you must be an expert on standards to deal with power circuit breakers. You can, however, begin to appreciate just how much effort, investment, and plain hard work goes into being able to legitimately print in a document a statement such as:
"Magnum DS Low Voltage Power Circuit Breakers are UL Listed and built and tested to all applicable ANSI Standards." Keep in mind that all these standards establish minimum requirements. There is nothing prohibiting a manufacturer from exceeding standards by offering additional features and/or using newer and improved operational techniques for more efficient and higher levels of performance. Magnum DS does just that in a number of areas.
The majority of the remaining discussions in this module will be presented as they relate to applicable ANSI Standards. Remember, however, that other standards do exist in other parts of the world. They must be complied with to participate in the international segment (Figure 38).
Figure 38. Circuit Breaker Identification
Low Voltage Power Circuit Breaker C37.50 Testing
Testing of a low voltage power circuit breaker in keeping with required ANSI Standards provides the first glimpse at what makes a low voltage power circuit breaker unique. Remember, low voltage power circuit breakers are applied at or below their nameplate ratings. That nameplate rating is a result of having successfully completed a series of rigorous tests. This is referred to as a 100% rating.
Although every detail of the testing will not be covered here, you will have an appreciation for just how demanding these ANSI defined tests are for low voltage power circuit breakers. The tests will be described as four test sequences. It should be pointed out here that all tests are performed using a Drawout circuit breaker in its enclosure for each frame size.
The first three test sequences are similar in many ways to the tests performed on other types of low voltage circuit breakers, such as a molded case circuit breaker. It is the fourth test sequence performed on a low voltage power circuit breaker that differentiates the power circuit breaker from other types of circuit breakers.
Note that all the following test sequences, except for Test Sequence 4 in which the circuit breaker has no Trip Unit, are preceded and followed by a calibration test and dielectric check.
Test Sequence 1 - This test sequence consists of a temperature rise test, an overload switching test, and then a short circuit test. The circuit breaker is equipped with an instantaneous trip.
1. The circuit breaker is loaded to 100% of the maximum rating of the frame size (in normal enclosure) until the temperature is constant. The standard lists the maximum permissible temperature rises at various parts of the circuit breaker.
2. The circuit breaker is then subjected to number of opening operations on over-load switching.
3. The circuit breaker is then given a 3-phase short circuit test at its maximum voltage rating, which is 635 volts for this 600 volt rated circuit breaker. The short circuit current in this case can be no less than the 600 volt interrupting capacity of the circuit breaker being tested. The three maximum voltages used during testing and typically listed on the nameplate are listed below along with their corresponding application voltages:
Maximum Voltage Application Voltage
635 volts 600 volts
508 volts 480 volts
254 volts 240 volts
4. The short circuit test consists of initiating current through the closed circuit breaker, causing it to trip. After 15 seconds, the circuit breaker is re-closed on the fault, and then allowed to trip open to clear the fault. This is known as an O-CO (open-close open) test.
5. The short circuit test is followed by a calibration check and a dielectric test.
Test Sequence 2 - This test sequence consists of a series of short circuit tests on a circuit breaker equipped with selective tripping (no instantaneous).
1. Once again, all short circuit tests are preceded by a dielectric test and a calibration test. After the interruptions, the circuit breaker is given another dielectric test and the calibration is again checked.
2. Each short circuit test is an O-CO test meaning that the circuit breaker interrupts the full fault current twice.
3. After the 3-phase short circuit tests are completed at different prescribed voltages, single phase tests are performed. A new circuit breaker may be used for each test, or each test may be done on different poles of the same circuit breaker.
4. One single-phase test is done at each of the same three maximum voltage ratings used for the three-phase tests (635, 508 and 254 volts) at the appropriate Interrupting Rating for that voltage.
Test Sequence 3 - This test sequence includes tests of mechanical and electrical endurance.
1. A circuit breaker is calibrated, given a dielectric test, and subjected to a large number of operations. Some of the operations are at no load and some at full load.
2. The required number of operations varies by circuit breaker frame size.
3. After the endurance test, the same circuit breaker is given a full 3-phase O-CO short circuit test at 635 volts and a dielectric withstand test.
The required number of operations for the endurance test just described is about the same for larger frame power circuit breakers and somewhat higher for smaller frame power circuit breakers compared to molded case circuit breaker endurance tests. For the sake of comparison, refer to the two endurance ratings tables, one for power circuit breakers and one for molded case circuit breakers .
Test Sequence 4 - This test sequence includes a short time current (withstand) test. Molded case and insulated case circuit breakers are not usually subjected to this type of test and, therefore, have no full 30 cycle Short Time Rating. This is one of the key differences.
1. For this test, the circuit breaker does not have a trip unit or the trip unit is disconnected. During the short-circuit testing, the circuit breaker can be tripped instantaneously by a shunt trip.
2. The circuit breaker is closed and then energized at its full short time current rating. The short time rating is usually equal to the 600 volt short circuit current rating.
3. The current is left on for 30 cycles (1/2 second), then off for 15 seconds, then back on for another 30 cycles. The circuit breaker remains closed during this test sequence.
4. After the short time current (withstand) tests, the same circuit breaker is given a 3-phase short circuit test sequence at full short circuit current rating and 635 volts. The circuit breaker is opened as quickly as possible by the shunt trip, which is energized at the same instant the power is applied. The intent is to force the circuit breaker to open during the worst case conditions (full current asymmetry). This is where the short time rating for the circuit breaker comes from.
5. After the final test, the circuit breaker calibration is checked and given a dielectric withstand test.
During Test Sequence 4, the circuit breaker is subjected to tremendous physical forces from the magnetic fields and to severe heating effects from the current. Think about it. Both the magnetic forces and the heating vary with the square of the current (Figure 41). For example, a 4000 ampere frame low voltage power circuit breaker at 85,000 amperes is subjected to forces and heating more than 450 times normal for each 30 cycle test. It is quite awesome.
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