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Page 3.1
Section
3
Overcurrent Protection
3.1.0
3.1.1
3.2.1
3.2.2
3.2.3
3.2.4
3.2.5
3.3.1
3.4.1
3.5.1
3.5.2
3.6.1
3.6.2
3.6.3
3.6.4
3.6.5
3.6.6
3.6.7
3.6.8
3.6.9
3.6.10
3.6.11
3.6.12
3.6.13
3.6.14
3.6.15
3.6.16
Introduction
NEC Section 90.2, Scope of the NEC
NEC Section 110.3(A)(5), (6), and (8), Requirements for Equipment
Selection
NEC Section 110.3(B), Requirements for Proper Installation of Listed
and Labeled Equipment
NEC Section 110.9, Requirements for Proper Interrupting Rating of
Overcurrent Protective Devices
NEC Section 110.10, Proper Protection of System Components from
Short Circuits
NEC Section 110.22, Proper Marking and Identification of Disconnecting
Means
NEC Section 210.20(A), Ratings of Overcurrent Devices on Branch
Circuits Serving Continuous and Noncontinuous Loads
NEC Section 215.10, Requirements for Ground-Fault Protection of
Equipment on Feeders
NEC Section 230.82, Equipment Allowed to Be Connected on the Line
Side of the Service Disconnect
NEC Section 230.95, Ground-Fault Protection for Services
NEC Section 240.1, Scope of Article 240 on Overcurrent Protection
NEC Section 240.3, Protection of Conductors Other than Flexible Cords
and Fixture Wires
NEC Section 240.4, Proper Protection of Fixture Wires and Flexible
Cords
NEC Section 240.6, Standard Ampere Ratings
NEC Sections 240.8 and 380.17, Protective Devices Used in Parallel
NEC Section 240.9, Thermal Devices
NEC Section 240.10, Requirements for Supplementary Overcurrent
Protection
NEC Section 240.11, Definition of Current-Limiting Overcurrent
Protective Devices
NEC Section 240.12, System Coordination or Selectivity
NEC Section 240.13, Ground-Fault Protection of Equipment on
Buildings or Remote Structures
NEC Section 240.21, Location Requirements for Overcurrent Devices
and Tap Conductors
NEC Section 240.40, Disconnecting Means for Fuses
NEC Section 240.50, Plug Fuses, Fuseholders, and Adapters
NEC Section 240.51, Edison-Base Fuses
NEC Section 240.53, Type S Fuses
NEC Section 240.54, Type S Fuses, Adapters, and Fuseholders
3.1
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Section Three
3.6.17
3.6.18
3.6.19
3.6.20
3.6.21
3.6.22
3.6.23
3.6.24
3.6.25
3.6.26
3.7.1
3.7.2
3.7.3
3.7.4
3.8.1
3.9.1
3.10.1
3.11.1
3.11.2
3.11.3
3.11.4
3.11.5
3.11.6
3.11.7
3.11.8
3.11.9
3.11.10
3.11.11
3.11.12
3.11.13
3.12.1
3.12.2
3.13.1
3.13.2
3.13.3
3.13.4
3.14.1
3.15.1
NEC Section 240.60, Cartridge Fuses and Fuseholders
NEC Section 240.61, Classification of Fuses and Fuseholders
NEC Section 240.86, Series Ratings
NEC Section 240.90, Supervised Industrial Installations
NEC Section 240.92(B), Transformer Secondary Conductors of Separately
Derived Systems (Supervised Industrial Installations Only)
NEC Section 240.92(B)(1), Short-Circuit and Ground-Fault Protection
(Supervised Industrial Installations Only)
NEC Section 240.92(B)(2), Overload Protection (Supervised Industrial
Installations Only)
NEC Section 240.92(C), Outside Feeder Taps (Supervised Industrial
Installations Only)
NEC Section 240.100, Feeder and Branch-Circuit Protection Over 600 V
Nominal
NEC Section 240.100(C), Conductor Protection
NEC Section 250.2(D), Performance of Fault-Current Path
NEC Section 250.90, Bonding Requirements and Short-Circuit Current
Rating
NEC Section 250.96(A), Bonding Other Enclosures and Short-Circuit
Current Requirements
NEC Section 250.122, Sizing of Equipment Grounding Conductors
NEC Section 310.10, Temperature Limitation of Conductors
NEC Section 364.11, Protection at a Busway Reduction
NEC Section 384.16, Panelboard Overcurrent Protection
NEC Section 430.1, Scope of Motor Article
NEC Section 430.6, Ampacity of Conductors for Motor Branch Circuits
and Feeders
NEC Section 430.8, Marking on Controllers
NEC Section 430.32, Motor Overload Protection
NEC Section 430.36, Fuses Used to Provide Overload and Single-Phasing
Protection
NEC Section 430.52, Sizing of Various Overcurrent Devices for Motor
Branch-Circuit Protection
NEC Section 430.53, Connecting Several Motors or Loads on One Branch
Circuit
NEC Section 430.71, Motor Control-Circuit Protection
NEC Section 430.72(A), Motor Control-Circuit Overcurrent Protection
NEC Section 430.72(B), Motor Control-Circuit Conductor Protection
NEC Section 430.72(C), Motor Control-Circuit Transformer Protection
NEC Section 430.94, Motor Control-Center Protection
NEC Section 430.109(A)(6), Manual Motor Controller as a Motor
Disconnect
NEC Section 440.5, Marking Requirements on HVAC Controllers
NEC Section 440.22, Application and Selection of the Branch-Circuit
Protection for HVAC Equipment
NEC Section 450.3, Protection Requirements for Transformers
NEC Section 450.3(A), Protection Requirements for Transformers Over
600 V
NEC Section 450.3(B), Protection Requirements for Transformers 600 V
or Less
NEC Section 450.6(A)(3), Tie-Circuit Protection
NEC Section 455.7, Overcurrent Protection Requirements for Phase
Converters
NEC Section 460.8(B), Overcurrent Protection of Capacitors
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Overcurrent Protection
3.16.1
3.17.1
3.18.1
3.19.1
3.20.1
3.21.1
3.22.1
3.23.1
3.23.2
3.23.3
3.24.1
3.25.1
3.26.1
3.1.0
3.3
NEC Section 501.6(B), Fuses for Class 1, Division 2 Locations
NEC Section 517.17, Requirements for Ground-Fault Protection and
Coordination in Health Care Facilities
NEC Section 520.53(F)(2), Protection of Portable Switchboards on Stage
NEC Section 550.6(B), Overcurrent Protection Requirements for Mobile
Homes and Parks
NEC Section 610.14(C), Conductor Sizes and Protection for Cranes and
Hoists
NEC Section 620.62, Selective Coordination of Overcurrent Protective
Devices for Elevators
NEC Section 670.3, Industrial Machinery
NEC Section 700.5, Emergency Systems: Their Capacity and Rating
NEC Section 700.16, Emergency Illumination
NEC Section 700.25, Emergency System Overcurrent Protection
Requirements (FPN)
NEC Section 705.16, Interconnected Electric Power Production Sources:
Interrupting and Short-Circuit Current Rating
NEC Section 725.23, Overcurrent Protection for Class 1 Circuits
NEC Section 760.23, Requirements for Non-Power-Limited Fire Alarm
Signaling Circuits
Introduction
In this section, a presentation format of questions and answers has been used to
focus on the factors that are pertinent to a basic understanding and application of
overcurrent protective devices. Relevant sections of the National Electrical Code
(NEC) are referenced and analyzed in detail. Each section is translated into simple,
easily understood language, complemented by one-line diagrams giving sound,
practical means of applying overcurrent protection, as well as affording compliance
with the NEC. The following is by permission of Cooper Bussmann, Inc.
3.1.1
NEC Section 90.2, Scope of the NEC
3.1.1
3.2.1 NEC Section 110.3(A)(5), (6), and (8)
Requirements for Equipment Selection
3.2.1
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Section Three
3.2.2 NEC Section 110.3(B), Requirements for
Proper Installation of Listed and Labeled Equipment
3.2.2
(continued)
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Overcurrent Protection
3.2.2
(Continued)
3.5
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Section Three
3.2.3 NEC Section 110.9, Requirements for Proper
Interrupting Rating of Overcurrent Protective Devices
3.2.3
(continued)
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Overcurrent Protection
3.2.3
3.7
(Continued)
(continued)
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Section Three
3.2.3
(Continued)
(continued)
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Overcurrent Protection
3.2.3
3.9
(Continued)
(continued)
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Section Three
3.2.3
(Continued)
(continued)
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Overcurrent Protection
3.2.3
3.11
(Continued)
(continued)
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Section Three
3.2.3
(Continued)
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Overcurrent Protection
3.13
3.2.4 NEC Section 110.10, Proper Protection
of System Components from Short Circuits
3.2.4
(continued)
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Section Three
3.2.4
(Continued)
(continued)
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Overcurrent Protection
3.2.4
(Continued)
3.15
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Section Three
3.2.5 NEC Section 110.22, Proper Marking and
Identification of Disconnecting Means
3.2.5
3.3.1 NEC Section 210.20(A), Ratings of
Overcurrent Devices on Branch Circuits Serving
Continuous and Noncontinuous Loads
3.3.1
3.4.1 NEC Section 215.10, Requirements for
Ground-Fault Protection of Equipment on Feeders
3.4.1
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Overcurrent Protection
3.17
3.5.1 NEC Section 230.82, Equipment Allowed to Be
Connected on the Line Side of the Service Disconnect
3.5.1
3.5.2 NEC Section 230.95, Ground-Fault
Protection for Services
3.5.2
(continued)
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Section Three
3.5.2
(Continued)
3.6.1 NEC Section 240.1, Scope of
Article 240 on Overcurrent Protection
3.6.1
(continued)
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Overcurrent Protection
3.6.1
(Continued)
3.6.2 NEC Section 240.3, Protection of Conductors
Other than Flexible Cords and Fixture Wires
3.6.2
3.19
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Section Three
3.6.3 NEC Section 240.4, Proper Protection of
Fixture Wires and Flexible Cords
3.6.3
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Overcurrent Protection
3.6.4
NEC Section 240.6, Standard Ampere Ratings
3.6.4
3.6.5 NEC Sections 240.8 and 380.17, Protective
Devices Used in Parallel
3.6.5
3.6.6
NEC Section 240.9, Thermal Devices
3.6.6
3.21
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Section Three
3.6.7 NEC Section 240.10, Requirements
for Supplementary Overcurrent Protection
3.6.7
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Overcurrent Protection
3.6.8 NEC Section 240.11, Definition of
Current-Limiting Overcurrent Protective Devices
(This article is not a part of the 2002 NEC, but is included for reference from
the 1999 NEC.)
3.6.8
3.23