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eLibrary >
ANSI NEMA C37.50-2018 (R2025) American National Standard for Switchgear-Low Voltage AC Power Circuit Breakers Used in Enclosures-Test Procedures >
ANSI NEMA C37.50-2018 (R2025) American National Standard for Switchgear-Low Voltage AC Power Circuit Breakers Used in Enclosures-Test Procedures, 2018
- 1 Scope
- 2 References [Go to Page]
- IEEE Std C37.26 Guide for Methods of Power-Factor Measurement for Low-Voltage (1000 Solid-State Trip Devices for use with Unfused Circuit Breakers AC or Lower) Inductive Test Circuits
- 3 General Test Conditions and Requirements
- 4 Design Test Requirements [Go to Page]
- 4.1 General
- 4.2 Specific Test Requirements [Go to Page]
- 4.2.1 Test Requirements for Unfused Circuit Breakers
- 4.2.2 Test Requirements for Fused Circuit Breakers
- 4.2.3 Test Requirements for Solid State Trip Devices
- 4.3 Test Conditions [Go to Page]
- 4.3.1 Test Enclosure
- 4.3.2 Circuit Breakers Using Only One Type of Trip Device
- 4.3.3 Circuit Breakers Using More than One Type of Trip Device [Go to Page]
- 4.3.3.1 Electromechanical Trip Devices
- Each circuit breaker frame size, with the electromechanical trip device installed, shall be tested for all applicable tests in accordance with the test sequences I, II, III, and IV of Table 1.
- 4.3.3.2 Solid-State Trip Devices for use with Unfused Circuit Breakers
- Each circuit breaker frame size, with the solid-state trip device installed, shall be tested in accordance with test sequence II given in Table 1, except that under (c), only short-circuit current test 3 need be performed.
- 4.3.3.3 Solid-State Trip Devices for use with Fused Circuit Breakers
- Each fused circuit breaker frame size shall be equipped with a solid-state trip device and shall be tested in accordance with Sequence V of Table 1.
- 4.4 Direct-Acting Overcurrent Trip Devices [Go to Page]
- 4.4.1 Trip-Device Calibration Check Test [Go to Page]
- 4.4.1.1 Long-Time-Delay Trip Elements
- 4.4.1.2 Instantaneous Trip Elements
- 4.4.1.3 Short-Time-Delay Trip Elements
- 4.4.1.4 Ground Trip Elements
- 4.4.1.5 Alternate Test Method
- 4.4.2 Electromagnetic compatibility tests [Go to Page]
- 4.4.2.1 Surge Withstand
- 4.4.2.2 Radiated Electromagnetic Interference
- 4.5 AC Dielectric Withstand-Voltage Test [Go to Page]
- 4.5.1 General
- 4.5.2 Test Voltages
- 4.5.3 Points of Application of Test Voltage [Go to Page]
- 4.5.3.1 Primary Circuits—Circuit Breaker Open
- With the circuit breaker in the open position, apply the primary circuit test potential between:
- 4.5.3.2 Primary Circuits—Circuit Breaker Closed
- With the circuit breaker in the closed position, apply the primary circuit test potential between:
- 4.5.3.3 Secondary Circuits
- With the circuit breaker in either the open or closed position, apply the secondary control wiring test potential between the secondary control wiring terminals and metal parts that are normally grounded.
- 4.6 Continuous-Current Test [Go to Page]
- 4.6.1 General
- 4.6.2 Duration of Test
- 4.6.3 Method of Measuring Temperature of the Air Surrounding the Enclosure (Ambient)
- 4.6.4 Copper Conductors for Use in Continuous-Current Tests
- 4.6.5 Method of Measuring Device Temperatures
- 4.6.6 Performance
- 4.7 Overload Switching Test [Go to Page]
- 4.7.1 General
- 4.7.2 Test Circuit
- 4.7.3 Rate of Operation
- 4.7.4 Opening of Circuit Breaker
- 4.7.5 Duration of Current
- 4.7.6 Number of Operations
- 4.7.7 Performance
- 4.8 Endurance Tests [Go to Page]
- 4.8.1 General [Go to Page]
- 4.8.1.1 Power Operated Circuit Breakers
- Power operated circuit breakers shall be subjected to all endurance tests.
- 4.8.1.2 Manually Operated Circuit Breakers (with Equivalent Power Operated Versions)
- Manually operated circuit breakers having stored-energy mechanisms that differ from the power operated equivalent only in the means of supplying the energy to be stored need not be subjected to endurance tests.
- 4.8.1.3 Manually Operated Circuit Breakers (without Equivalent Power Operated Versions)
- Manually operated circuit breakers, not essentially the same as power operated circuit breakers or not having any power operated equivalent, shall be subjected to all endurance tests except that the number of mechanical endurance operations performed ...
- 4.8.2 Rate of Operation
- 4.8.3 Electrical Endurance Test [Go to Page]
- 4.8.3.1 Test Circuit
- 4.8.4 Mechanical Endurance Test
- 4.8.5 Performance
- 4.9 Short-Circuit Current Tests [Go to Page]
- 4.9.1 General
- 4.9.2 Types of Tests [Go to Page]
- 4.9.2.1 Single-Phase, Single-Pole Tests
- Single-phase tests with a line-to-line voltage not less than each rated maximum voltage applied across any pole and with the available rms symmetrical current not less than 87% of the applicable rated three-phase short-circuit current. See Table 4, te...
- 4.9.2.2 Three-Phase, Three-Pole Tests
- Three-phase tests with a line-to-line voltage not less than each rated maximum voltage and the average of the available rms symmetrical components of the available three-phase currents not less than the applicable rated short-circuit current. See Tabl...
- 4.9.2.3 Fused Circuit Breaker Intermediate Short-Circuit Test A
- For fused circuit breakers, a three-phase test with a line-to-line voltage not less than rated maximum voltage and the average of the available rms symmetrical components of the available three-phase currents between 90% and 100% of the short-circuit ...
- 4.9.2.4 Fused Circuit Breaker Intermediate Short-Circuit Test B
- For fused circuit breakers, a three-phase test with a line-to-line voltage not less than rated maximum voltage and the average of the available rms symmetrical components of the available three-phase currents between 90% and 110% of the short-circuit ...
- 4.9.3 Test Circuit Conditions [Go to Page]
- 4.9.3.1 RMS Symmetrical Current
- 4.9.3.2 Power Factor
- The power factor of the test circuit for unfused circuit breakers shall be 15% lagging or less (X/R ratio of 6.6 or greater) with X and R in series connection. Any reactor used in the test circuit shall be an air-core reactor. The power factor for fus...
- 4.9.3.3 Transient Current Characteristics
- Transient current characteristics of the test circuit shall be as given in 4.9.3.3.1 through 4.9.3.3.4. [Go to Page]
- 4.9.3.3.1 Unfused Circuit Breakers With Instantaneous
- For circuit breakers with instantaneous trip elements the rms value of the alternating component of the current at the end of three cycles shall be not less than 90% of the value measured at one-half cycle after initiation of the current.
- 4.9.3.3.2 Unfused Circuit Breakers Without Instantaneous
- For unfused circuit breakers without instantaneous trip elements the rms value of the alternating components of the current at the end of 1/2 second shall be not less than 80% of the value measured at one-half cycle after initiation of the current.
- 4.9.3.3.3 Peak Current (Unfused Circuit Breakers)
- For the first opening operation (unfused circuit breakers) on each duty cycle, the current shall be initiated in the test circuit in such a manner as to ensure that the peak current available would be not less than 2.3 times the single-phase rms symme...
- 4.9.3.3.4 Peak Current (Fused Circuit Breakers)
- For the first opening operation (fused circuit breakers) on each duty cycle, the current shall be initiated in the test circuit in such a manner as to ensure that the peak current available would be not less than 2.16 times the single-phase rms symmet...
- 4.9.3.4 Voltage
- The test-circuit voltage prior to the inception of current flow shall be not less than the rated maximum voltage for the short-circuit current rating being verified.
- 4.9.3.5 Frequency of the test circuit
- 4.9.3.5.1 Circuit breakers rated 50 Hz
- The power frequency of the test circuit for a circuit breaker with a rated power frequency of 50 Hz shall be 50 Hz ±5%.
- 4.9.3.5.2 Circuit breakers rated 60 Hz
- The power frequency of the test circuit for a circuit breaker with a rated power frequency of 60 Hz shall be 60 Hz ±5%.
- 4.9.3.5.3 Circuit breakers rated 50/60 Hz
- For a circuit breaker with a rated power frequency of 50/60 Hz:
- a. When the published tolerance bands of the time-current curves of the circuit breaker direct-acting trip systems at 50 Hz do not fall entirely within the published tolerance bands of the time-current curves at 60 Hz, the circuit breaker shall be tes...
- 1. The circuit breaker shall be tested at both 50 Hz ±5% and 60 Hz ±5% for an unfused circuit breaker with clearing time of less than one power frequency cycle2F .
- 2. The circuit breaker shall be tested at either 50 Hz ±5% or 60 Hz ±5% for an unfused circuit breaker with clearing time of one power frequency cycle3 or more.
- 3. The circuit breaker shall be tested at both 50 Hz ±5% and 60 Hz ±5% for a fused circuit breaker, if the clearing time of the circuit breaker element (without fuses) is less than one power frequency cycle3.
- 4. The circuit breaker shall be tested at either 50 Hz ±5% or 60 Hz ±5% for a fused circuit breaker, if the clearing time of the circuit breaker element (without fuses) is one power frequency cycle3 or more.
- 4.9.3.6 Primary Circuit Grounding
- On three-phase tests, either the power source or fault connections shall be grounded, but not both.
- 4.9.3.7 Power-Frequency Recovery Voltage
- The power-frequency recovery voltage shall be not less than 95% of the rated maximum voltage of the circuit breaker when testing with instantaneous trip elements. When testing circuit breakers without instantaneous trip elements, the recovery voltage ...
- 4.9.3.8 Enclosure Grounding for Three-Phase Tests
- For three-phase testing, the enclosure and the frame of the circuit breaker shall be insulated from ground and shall be connected through a 30-ampere fuse of adequate interrupting rating to the line side of the phase judged least likely to strike to t...
- 4.9.3.9 Enclosure Grounding for Single-Phase Tests
- For single-phase testing, the test enclosure and circuit breaker frame shall be insulated from ground and shall be connected through a 30-ampere fuse of adequate interrupting rating to the unused phase of the three-phase source. As an alternate config...
- 4.9.4 Circuit Breaker Direct-Acting Trip-Device Settings [Go to Page]
- 4.9.4.1 General [Go to Page]
- 4.9.4.1.1 LI Trip Devices and Settings
- For test sequences II and III, circuit breakers shall be equipped with direct-acting trip devices with long-time-delay and instantaneous elements. The continuous-current rating of the trip device shall be equal to the circuit breaker frame size being ...
- 4.9.4.1.2 LS Trip Devices and Settings
- For test sequence I, circuit breakers shall be equipped with direct-acting trip devices with long-time-delay and short- time-delay trip elements. The continuous-current rating of the trip devices shall be equal to the circuit breaker frame size being ...
- 4.9.4.2 Minimum-Rated Trip Devices
- Ratings and setting of unfused circuit breaker direct-acting trip devices that shall be used for test sequence II(c), test 2, to demonstrate withstand-ability of the minimum-rated trip devices are specified in 4.9.4.2.1 and 4.9.4.2.2. [Go to Page]
- 4.9.4.2.1 LI Trip Device and Settings
- The circuit breakers shall be equipped with direct-acting trip devices with long-time-delay and instantaneous trip elements. The continuous rating of the trip device shall be the minimum continuous-current rating at 480 V for the circuit breaker frame...
- 4.9.4.2.2 Additional Considerations
- Where no change of the integral series conductor is involved, only the maximum rating of the frame size need be checked as stated in 4.9.4.1.1. However, for solid-state trip devices, the lowest-ratio current-transformer (sensor) shall be used.
- 4.9.4.3 Maximum Energy Test
- For solid-state trip devices an additional interrupting test (not required to be part of Sequence I) shall be conducted as indicated in Table 4, Test 8, with the lowest-ratio current-transformer (sensor), short time-delay element set at maximum pickup...
- 4.9.4.4 LI Trip Devices and Settings for Fused Circuit Breakers
- Fused circuit breakers shall be equipped with direct-acting trip devices with long-time-delay and instantaneous elements. The long-time-delay element’s pickup and time setting may be set as desired by the manufacturer, but the instantaneous setting sh...
- 4.9.4.5 Qualification of Additional Solid-State Trip Devices
- When a solid-state trip device of new design is added to existing qualified circuit breakers, the following tests shall be conducted:
- 4.9.5 Short-Circuit Current Duty Cycle
- 4.9.6 Test Procedure
- 4.9.7 Emission Indicators for Short-Circuit Current Tests
- 4.9.8 Performance [Go to Page]
- 4.9.8.1 Acceptance Criteria for Unfused Circuit Breakers
- The unfused circuit breaker at the conclusion of each test shall be in a condition to continue the applicable test sequence without repair or replacement of parts, except as permitted in Note 3 of Table 1, and the emission indicators shall not have ig...
- 4.9.8.2 Acceptance Criteria for Fused Circuit Breakers
- The fused circuit breaker at the conclusion of each test shall be in a condition to complete the test sequence (tests (e) and (f) of sequence V, Table 1) without repairs or replacement of parts other than the primary fuses and open-fuse trip- device t...
- 4.9.9 Making Current
- 4.9.10 Latching Current
- 4.10 Short-Time Current Test [Go to Page]
- 4.10.1 General
- 4.10.2 Test Circuit
- 4.10.3 Test Procedure
- 4.10.4 Short-Time Current Duty Cycle
- 4.10.5 Performance
- 5 Accessory Devices [Go to Page]
- 5.1 General
- 5.2 Alarm and Auxiliary Switches [Go to Page]
- 5.2.1 Temperature Test
- 5.2.2 Overload Test [Go to Page]
- 5.2.2.1 Performance
- 5.2.3 Endurance Test—Auxiliary Switch [Go to Page]
- 5.2.3.1 Performance
- 5.3 Undervoltage Trip Devices [Go to Page]
- 5.3.1 General
- 5.3.2 Temperature Test
- 5.3.3 Operation Test
- 5.3.4 Endurance Test
- 5.4 Mechanical Accessory Devices
- 6 Treatment of Failures within Test Sequences
- 7 Production Tests (Routine Tests) [Go to Page]
- 7.1 General
- 7.2 Calibration [Go to Page]
- 7.2.1 General
- 7.2.2 Direct-Acting Trip Devices
- 7.2.3 Undervoltage Trip Devices
- 7.3 Control, Secondary Wiring, and Devices Check Test
- 7.4 AC Dielectric Withstand Test
- 7.5 No-Load Operation Test [Go to Page]
- 7.5.1 Power Operated Circuit Breakers
- 7.5.2 Manually Operated Circuit Breakers
- 7.6 Open-Fuse Trip Device
- 8 Production Monitoring and Product Retest Requirements [Go to Page]
- 8.1 General [Go to Page]
- 8.1.1 General (Fused Circuit Breakers)
- 8.2 Production Monitoring
- 8.3 Product Retest Requirements [Go to Page]
- 8.3.1 Product Retest Requirements (Fused Circuit Breakers) [Go to Page]
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