Circuit Breaker Reference

Low-voltage circuit breakers

Updated 2026-10-13

A low-voltage circuit breaker is a circuit breaker built for low-voltage power circuits, a class whose constructions include the molded-case breaker, the insulated-case breaker and the low-voltage power circuit breaker. [1] [2] In the definition given by 29 CFR 1910.399, a circuit breaker is a device that opens and closes a circuit by nonautomatic means and opens it automatically on a predetermined overcurrent without damage to itself when properly applied within its rating. [3]

Description

The acceptance standard places molded-case breakers in section 7.6.1.1.1, insulated-case breakers in section 7.6.1.1.2 and low-voltage power circuit breakers in section 7.6.1.2. [2] ANSI/NETA MTS-2023 groups insulated-case and molded-case breakers together in section 7.6.1.1 and treats low-voltage power circuit breakers in section 7.6.1.2. [4]

Tests at acceptance

Acceptance testing under ANSI/NETA ATS-2025 begins with visual and mechanical inspection for all three constructions. [5] The insulation and the current path are examined by insulation resistance tests and by contact or pole resistance measurements. [6] [7]

The protective functions are proven by trip tests with primary current injection, by secondary injection of the trip unit and by tests of ground-fault protection functions. [8] [9] [10] For insulated-case and low-voltage power circuit breakers, control and functional operation is verified as well. [11]

Tests in maintenance

ANSI/NETA MTS-2023 covers the same constructions in maintenance testing, again beginning with visual and mechanical inspection. [12] Insulation resistance tests and contact or pole resistance measurements recheck the insulation and the current path. [13] [14]

Primary current injection, secondary injection of the trip unit and ground-fault protection tests recheck the protective functions. [15] [16] [17] Minimum pickup tests of the trip and close coils apply to insulated-case and molded-case breakers, and control and functional verification applies to low-voltage power circuit breakers. [18] [19]

Governing standards

The breaker sections of ANSI/NETA ATS-2025 refer to Table 100.1 for insulation resistance, to Table 100.7 for inverse-time trip testing of molded-case breakers and to Table 100.8 for instantaneous trip tolerances. [20] The corresponding sections of ANSI/NETA MTS-2023 refer to its own Table 100.1 and, for insulated-case and molded-case breakers, to its Table 100.7 and Table 100.8. [21] The numerical criteria are set out in those tables. [20] [21]

The definition of the device given in the lead is the regulatory one in 29 CFR 1910.399. [3]

Notes

  1. Electrical Testing Reference editorial taxonomy, 2026-10 edition. A low-voltage circuit breaker is a circuit breaker built for low-voltage power circuits, a class that takes in molded-case, insulated-case and low-voltage power circuit breakers. Datum equip.low-voltage-circuit-breakers.definition
  2. ANSI/NETA ATS-2025, clause 7.6.1.1.1, 7.6.1.1.2, 7.6.1.2. ANSI/NETA ATS-2025 treats low-voltage circuit breakers in separate sections for molded-case breakers (7.6.1.1.1), insulated-case breakers (7.6.1.1.2) and power circuit breakers (7.6.1.2). Datum equip.low-voltage-circuit-breakers.ats-sections
  3. 29 CFR 1910.399, current edition, clause 1910.399. 29 CFR 1910.399 defines a circuit breaker as a device designed to open and close a circuit by nonautomatic means and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within its rating. Datum equip.low-voltage-circuit-breakers.osha-definition
  4. ANSI/NETA MTS-2023, clause 7.6.1.1, 7.6.1.2. ANSI/NETA MTS-2023 treats insulated-case and molded-case breakers together in section 7.6.1.1 and low-voltage power circuit breakers in section 7.6.1.2. Datum equip.low-voltage-circuit-breakers.mts-sections
  5. ANSI/NETA ATS-2025, clause 7.6.1.1.1.A, 7.6.1.1.2.A, 7.6.1.2.A. ANSI/NETA ATS-2025 opens its sections on molded-case, insulated-case and low-voltage power circuit breakers with visual and mechanical inspection. Datum equip.low-voltage-circuit-breakers.acc.visual-mechanical
  6. ANSI/NETA ATS-2025, clause 7.6.1.1.1.B.1, 7.6.1.1.2.B.1, 7.6.1.2.B.1. ANSI/NETA ATS-2025 calls for insulation resistance tests on molded-case, insulated-case and low-voltage power circuit breakers at acceptance. Datum equip.low-voltage-circuit-breakers.acc.insulation-resistance
  7. ANSI/NETA ATS-2025, clause 7.6.1.1.1.B.2, 7.6.1.1.2.B.2, 7.6.1.2.B.2. ANSI/NETA ATS-2025 calls for contact or pole resistance measurements on molded-case, insulated-case and low-voltage power circuit breakers at acceptance. Datum equip.low-voltage-circuit-breakers.acc.contact-resistance
  8. ANSI/NETA ATS-2025, clause 7.6.1.1.1.B.3, 7.6.1.1.2.B.3, 7.6.1.2.B.3. ANSI/NETA ATS-2025 calls for trip tests by primary current injection on molded-case, insulated-case and low-voltage power circuit breakers at acceptance. Datum equip.low-voltage-circuit-breakers.acc.primary-injection
  9. ANSI/NETA ATS-2025, clause 7.6.1.1.1.B.7, 7.6.1.1.2.B.7, 7.6.1.2.B.7. ANSI/NETA ATS-2025 calls for secondary injection tests of the trip unit on molded-case, insulated-case and low-voltage power circuit breakers at acceptance. Datum equip.low-voltage-circuit-breakers.acc.secondary-injection
  10. ANSI/NETA ATS-2025, clause 7.6.1.1.1.B.5, 7.6.1.1.2.B.5, 7.6.1.2.B.5. ANSI/NETA ATS-2025 calls for tests of ground-fault protection functions on molded-case, insulated-case and low-voltage power circuit breakers at acceptance. Datum equip.low-voltage-circuit-breakers.acc.ground-fault
  11. ANSI/NETA ATS-2025, clause 7.6.1.1.2.B.8, 7.6.1.2.B.8. ANSI/NETA ATS-2025 calls for verification of control and functional operation on insulated-case and low-voltage power circuit breakers at acceptance. Datum equip.low-voltage-circuit-breakers.acc.control-functional
  12. ANSI/NETA MTS-2023, clause 7.6.1.1.A, 7.6.1.2.A. ANSI/NETA MTS-2023 opens its sections on insulated-case and molded-case breakers and on low-voltage power circuit breakers with visual and mechanical inspection. Datum equip.low-voltage-circuit-breakers.mnt.visual-mechanical
  13. ANSI/NETA MTS-2023, clause 7.6.1.1.B.2, 7.6.1.2.B.2. ANSI/NETA MTS-2023 calls for insulation resistance tests on insulated-case, molded-case and low-voltage power circuit breakers in maintenance testing. Datum equip.low-voltage-circuit-breakers.mnt.insulation-resistance
  14. ANSI/NETA MTS-2023, clause 7.6.1.1.B.3, 7.6.1.2.B.3. ANSI/NETA MTS-2023 calls for contact or pole resistance measurements on insulated-case, molded-case and low-voltage power circuit breakers in maintenance testing. Datum equip.low-voltage-circuit-breakers.mnt.contact-resistance
  15. ANSI/NETA MTS-2023, clause 7.6.1.1.B.5, 7.6.1.2.B.5. ANSI/NETA MTS-2023 calls for trip tests by primary current injection on insulated-case, molded-case and low-voltage power circuit breakers in maintenance testing. Datum equip.low-voltage-circuit-breakers.mnt.primary-injection
  16. ANSI/NETA MTS-2023, clause 7.6.1.1.B.9, 7.6.1.2.B.9. ANSI/NETA MTS-2023 calls for secondary injection tests of the trip unit on insulated-case, molded-case and low-voltage power circuit breakers in maintenance testing. Datum equip.low-voltage-circuit-breakers.mnt.secondary-injection
  17. ANSI/NETA MTS-2023, clause 7.6.1.1.B.7, 7.6.1.2.B.7. ANSI/NETA MTS-2023 calls for tests of ground-fault protection functions on insulated-case, molded-case and low-voltage power circuit breakers in maintenance testing. Datum equip.low-voltage-circuit-breakers.mnt.ground-fault
  18. ANSI/NETA MTS-2023, clause 7.6.1.1.B.10. ANSI/NETA MTS-2023 calls for minimum pickup tests of trip and close coils on insulated-case and molded-case breakers in maintenance testing. Datum equip.low-voltage-circuit-breakers.mnt.coil-pickup
  19. ANSI/NETA MTS-2023, clause 7.6.1.2.B.11. ANSI/NETA MTS-2023 calls for verification of control and functional operation on low-voltage power circuit breakers in maintenance testing. Datum equip.low-voltage-circuit-breakers.mnt.control-functional
  20. ANSI/NETA ATS-2025, clause 7.6.1.1.1, 7.6.1.1.2, 7.6.1.2. The ANSI/NETA ATS-2025 sections on low-voltage circuit breakers refer to Table 100.1 for insulation resistance, to Table 100.7 for inverse-time trip testing of molded-case breakers and to Table 100.8 for instantaneous trip tolerances. Datum equip.low-voltage-circuit-breakers.ats-tables
  21. ANSI/NETA MTS-2023, clause 7.6.1.1, 7.6.1.2. The ANSI/NETA MTS-2023 sections on low-voltage circuit breakers refer to Table 100.1 for insulation resistance, and the insulated-case and molded-case section also refers to Table 100.7 for inverse-time trip testing and to Table 100.8 for instantaneous trip tolerances. Datum equip.low-voltage-circuit-breakers.mts-tables

Data records

  • ANSI/NETA ATS-2025 calls for contact or pole resistance measurements on molded-case, insulated-case and low-voltage power circuit breakers at acceptance. Source: ANSI/NETA ATS-2025, clause 7.6.1.1.1.B.2, 7.6.1.1.2.B.2, 7.6.1.2.B.2. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.acc.contact-resistance
  • ANSI/NETA ATS-2025 calls for verification of control and functional operation on insulated-case and low-voltage power circuit breakers at acceptance. Source: ANSI/NETA ATS-2025, clause 7.6.1.1.2.B.8, 7.6.1.2.B.8. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.acc.control-functional
  • ANSI/NETA ATS-2025 calls for tests of ground-fault protection functions on molded-case, insulated-case and low-voltage power circuit breakers at acceptance. Source: ANSI/NETA ATS-2025, clause 7.6.1.1.1.B.5, 7.6.1.1.2.B.5, 7.6.1.2.B.5. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.acc.ground-fault
  • ANSI/NETA ATS-2025 calls for insulation resistance tests on molded-case, insulated-case and low-voltage power circuit breakers at acceptance. Source: ANSI/NETA ATS-2025, clause 7.6.1.1.1.B.1, 7.6.1.1.2.B.1, 7.6.1.2.B.1. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.acc.insulation-resistance
  • ANSI/NETA ATS-2025 calls for trip tests by primary current injection on molded-case, insulated-case and low-voltage power circuit breakers at acceptance. Source: ANSI/NETA ATS-2025, clause 7.6.1.1.1.B.3, 7.6.1.1.2.B.3, 7.6.1.2.B.3. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.acc.primary-injection
  • ANSI/NETA ATS-2025 calls for secondary injection tests of the trip unit on molded-case, insulated-case and low-voltage power circuit breakers at acceptance. Source: ANSI/NETA ATS-2025, clause 7.6.1.1.1.B.7, 7.6.1.1.2.B.7, 7.6.1.2.B.7. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.acc.secondary-injection
  • ANSI/NETA ATS-2025 opens its sections on molded-case, insulated-case and low-voltage power circuit breakers with visual and mechanical inspection. Source: ANSI/NETA ATS-2025, clause 7.6.1.1.1.A, 7.6.1.1.2.A, 7.6.1.2.A. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.acc.visual-mechanical
  • ANSI/NETA ATS-2025 treats low-voltage circuit breakers in separate sections for molded-case breakers (7.6.1.1.1), insulated-case breakers (7.6.1.1.2) and power circuit breakers (7.6.1.2). Source: ANSI/NETA ATS-2025, clause 7.6.1.1.1, 7.6.1.1.2, 7.6.1.2. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.ats-sections
  • The ANSI/NETA ATS-2025 sections on low-voltage circuit breakers refer to Table 100.1 for insulation resistance, to Table 100.7 for inverse-time trip testing of molded-case breakers and to Table 100.8 for instantaneous trip tolerances. Source: ANSI/NETA ATS-2025, clause 7.6.1.1.1, 7.6.1.1.2, 7.6.1.2. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.ats-tables
  • A low-voltage circuit breaker is a circuit breaker built for low-voltage power circuits, a class that takes in molded-case, insulated-case and low-voltage power circuit breakers. Source: Electrical Testing Reference editorial taxonomy, 2026-10 edition. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.definition
  • ANSI/NETA MTS-2023 calls for minimum pickup tests of trip and close coils on insulated-case and molded-case breakers in maintenance testing. Source: ANSI/NETA MTS-2023, clause 7.6.1.1.B.10. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.mnt.coil-pickup
  • ANSI/NETA MTS-2023 calls for contact or pole resistance measurements on insulated-case, molded-case and low-voltage power circuit breakers in maintenance testing. Source: ANSI/NETA MTS-2023, clause 7.6.1.1.B.3, 7.6.1.2.B.3. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.mnt.contact-resistance
  • ANSI/NETA MTS-2023 calls for verification of control and functional operation on low-voltage power circuit breakers in maintenance testing. Source: ANSI/NETA MTS-2023, clause 7.6.1.2.B.11. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.mnt.control-functional
  • ANSI/NETA MTS-2023 calls for tests of ground-fault protection functions on insulated-case, molded-case and low-voltage power circuit breakers in maintenance testing. Source: ANSI/NETA MTS-2023, clause 7.6.1.1.B.7, 7.6.1.2.B.7. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.mnt.ground-fault
  • ANSI/NETA MTS-2023 calls for insulation resistance tests on insulated-case, molded-case and low-voltage power circuit breakers in maintenance testing. Source: ANSI/NETA MTS-2023, clause 7.6.1.1.B.2, 7.6.1.2.B.2. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.mnt.insulation-resistance
  • ANSI/NETA MTS-2023 calls for trip tests by primary current injection on insulated-case, molded-case and low-voltage power circuit breakers in maintenance testing. Source: ANSI/NETA MTS-2023, clause 7.6.1.1.B.5, 7.6.1.2.B.5. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.mnt.primary-injection
  • ANSI/NETA MTS-2023 calls for secondary injection tests of the trip unit on insulated-case, molded-case and low-voltage power circuit breakers in maintenance testing. Source: ANSI/NETA MTS-2023, clause 7.6.1.1.B.9, 7.6.1.2.B.9. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.mnt.secondary-injection
  • ANSI/NETA MTS-2023 opens its sections on insulated-case and molded-case breakers and on low-voltage power circuit breakers with visual and mechanical inspection. Source: ANSI/NETA MTS-2023, clause 7.6.1.1.A, 7.6.1.2.A. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.mnt.visual-mechanical
  • ANSI/NETA MTS-2023 treats insulated-case and molded-case breakers together in section 7.6.1.1 and low-voltage power circuit breakers in section 7.6.1.2. Source: ANSI/NETA MTS-2023, clause 7.6.1.1, 7.6.1.2. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.mts-sections
  • The ANSI/NETA MTS-2023 sections on low-voltage circuit breakers refer to Table 100.1 for insulation resistance, and the insulated-case and molded-case section also refers to Table 100.7 for inverse-time trip testing and to Table 100.8 for instantaneous trip tolerances. Source: ANSI/NETA MTS-2023, clause 7.6.1.1, 7.6.1.2. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.mts-tables
  • 29 CFR 1910.399 defines a circuit breaker as a device designed to open and close a circuit by nonautomatic means and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within its rating. Source: 29 CFR 1910.399, current edition, clause 1910.399. Verified 2026-10-13. Record equip.low-voltage-circuit-breakers.osha-definition

Sources

  • 29 CFR 1910.399, 1910.399 - Definitions applicable to this subpart, current edition, OSHA. Cited: clause 1910.399. Held as: Government work. Publisher page
  • ANSI/NETA ATS-2025, Acceptance Testing Specifications for Electrical Power Equipment and Systems, 2025 edition, NETA. Cited: clause 7.6.1.1.1, 7.6.1.1.2, 7.6.1.2; clause 7.6.1.1.1.A, 7.6.1.1.2.A, 7.6.1.2.A; clause 7.6.1.1.1.B.1, 7.6.1.1.2.B.1, 7.6.1.2.B.1; clause 7.6.1.1.1.B.2, 7.6.1.1.2.B.2, 7.6.1.2.B.2; clause 7.6.1.1.1.B.3, 7.6.1.1.2.B.3, 7.6.1.2.B.3; clause 7.6.1.1.1.B.7, 7.6.1.1.2.B.7, 7.6.1.2.B.7; clause 7.6.1.1.1.B.5, 7.6.1.1.2.B.5, 7.6.1.2.B.5; clause 7.6.1.1.2.B.8, 7.6.1.2.B.8. Held as: Purchased single-user copy. Publisher page
  • ANSI/NETA MTS-2023, Maintenance Testing Specifications for Electrical Power Equipment and Systems, 2023 edition, NETA. Cited: clause 7.6.1.1, 7.6.1.2; clause 7.6.1.1.A, 7.6.1.2.A; clause 7.6.1.1.B.2, 7.6.1.2.B.2; clause 7.6.1.1.B.3, 7.6.1.2.B.3; clause 7.6.1.1.B.5, 7.6.1.2.B.5; clause 7.6.1.1.B.9, 7.6.1.2.B.9; clause 7.6.1.1.B.7, 7.6.1.2.B.7; clause 7.6.1.1.B.10; clause 7.6.1.2.B.11. Held as: Purchased single-user copy. Publisher page
  • Electrical Testing Reference editorial taxonomy, Electrical Testing Reference editorial taxonomy of test methods, 2026-10 edition, Electrical Testing Reference. Held as: Own observation.

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"Low-voltage circuit breakers." Circuit Breaker Reference. Revision 1, 2026-10-13. https://www.circuitbreakerreference.com/equipment/low-voltage-circuit-breakers/rev/1/.