overcurrent protection

3Overcurrent Protection

3.1.0 Introduction3.1.1 NEC Section 90.2, Scope of the NEC3.2.1 NEC Section 110.3(A)(5), (6), and (8), Requirements for Equipment

Selection3.2.2 NEC Section 110.3(B), Requirements for Proper Installation of Listed

and Labeled Equipment3.2.3 NEC Section 110.9, Requirements for Proper Interrupting Rating of

Overcurrent Protective Devices3.2.4 NEC Section 110.10, Proper Protection of System Components from

Short Circuits3.2.5 NEC Section 110.22, Proper Marking and Identification of Disconnecting

Means3.3.1 NEC Section 210.20(A), Ratings of Overcurrent Devices on Branch

Circuits Serving Continuous and Noncontinuous Loads3.4.1 NEC Section 215.10, Requirements for Ground-Fault Protection of

Equipment on Feeders3.5.1 NEC Section 230.82, Equipment Allowed to Be Connected on the Line

Side of the Service Disconnect3.5.2 NEC Section 230.95, Ground-Fault Protection for Services3.6.1 NEC Section 240.1, Scope of Article 240 on Overcurrent Protection3.6.2 NEC Section 240.3, Protection of Conductors Other than Flexible Cords

and Fixture Wires3.6.3 NEC Section 240.4, Proper Protection of Fixture Wires and Flexible

Cords3.6.4 NEC Section 240.6, Standard Ampere Ratings3.6.5 NEC Sections 240.8 and 380.17, Protective Devices Used in Parallel3.6.6 NEC Section 240.9, Thermal Devices3.6.7 NEC Section 240.10, Requirements for Supplementary Overcurrent

Protection3.6.8 NEC Section 240.11, Definition of Current-Limiting Overcurrent

Protective Devices3.6.9 NEC Section 240.12, System Coordination or Selectivity3.6.10 NEC Section 240.13, Ground-Fault Protection of Equipment on

Buildings or Remote Structures3.6.11 NEC Section 240.21, Location Requirements for Overcurrent Devices

and Tap Conductors3.6.12 NEC Section 240.40, Disconnecting Means for Fuses3.6.13 NEC Section 240.50, Plug Fuses, Fuseholders, and Adapters3.6.14 NEC Section 240.51, Edison-Base Fuses3.6.15 NEC Section 240.53, Type S Fuses3.6.16 NEC Section 240.54, Type S Fuses, Adapters, and Fuseholders

Section

3.1

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3.6.17 NEC Section 240.60, Cartridge Fuses and Fuseholders3.6.18 NEC Section 240.61, Classification of Fuses and Fuseholders3.6.19 NEC Section 240.86, Series Ratings3.6.20 NEC Section 240.90, Supervised Industrial Installations3.6.21 NEC Section 240.92(B), Transformer Secondary Conductors of Separately

Derived Systems (Supervised Industrial Installations Only)3.6.22 NEC Section 240.92(B)(1), Short-Circuit and Ground-Fault Protection

(Supervised Industrial Installations Only)3.6.23 NEC Section 240.92(B)(2), Overload Protection (Supervised Industrial

Installations Only)3.6.24 NEC Section 240.92(C), Outside Feeder Taps (Supervised Industrial

Installations Only)3.6.25 NEC Section 240.100, Feeder and Branch-Circuit Protection Over 600 V

Nominal3.6.26 NEC Section 240.100(C), Conductor Protection3.7.1 NEC Section 250.2(D), Performance of Fault-Current Path3.7.2 NEC Section 250.90, Bonding Requirements and Short-Circuit Current

Rating3.7.3 NEC Section 250.96(A), Bonding Other Enclosures and Short-Circuit

Current Requirements3.7.4 NEC Section 250.122, Sizing of Equipment Grounding Conductors3.8.1 NEC Section 310.10, Temperature Limitation of Conductors3.9.1 NEC Section 364.11, Protection at a Busway Reduction3.10.1 NEC Section 384.16, Panelboard Overcurrent Protection3.11.1 NEC Section 430.1, Scope of Motor Article3.11.2 NEC Section 430.6, Ampacity of Conductors for Motor Branch Circuits

and Feeders3.11.3 NEC Section 430.8, Marking on Controllers3.11.4 NEC Section 430.32, Motor Overload Protection3.11.5 NEC Section 430.36, Fuses Used to Provide Overload and Single-Phasing

Protection3.11.6 NEC Section 430.52, Sizing of Various Overcurrent Devices for Motor

Branch-Circuit Protection3.11.7 NEC Section 430.53, Connecting Several Motors or Loads on One Branch

Circuit3.11.8 NEC Section 430.71, Motor Control-Circuit Protection3.11.9 NEC Section 430.72(A), Motor Control-Circuit Overcurrent Protection3.11.10 NEC Section 430.72(B), Motor Control-Circuit Conductor Protection3.11.11 NEC Section 430.72(C), Motor Control-Circuit Transformer Protection3.11.12 NEC Section 430.94, Motor Control-Center Protection3.11.13 NEC Section 430.109(A)(6), Manual Motor Controller as a Motor

Disconnect3.12.1 NEC Section 440.5, Marking Requirements on HVAC Controllers3.12.2 NEC Section 440.22, Application and Selection of the Branch-Circuit

Protection for HVAC Equipment3.13.1 NEC Section 450.3, Protection Requirements for Transformers3.13.2 NEC Section 450.3(A), Protection Requirements for Transformers Over

600 V3.13.3 NEC Section 450.3(B), Protection Requirements for Transformers 600 V

or Less3.13.4 NEC Section 450.6(A)(3), Tie-Circuit Protection3.14.1 NEC Section 455.7, Overcurrent Protection Requirements for Phase

Converters3.15.1 NEC Section 460.8(B), Overcurrent Protection of Capacitors

3.2 Section Three

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Overcurrent Protection 3.3

3.16.1 NEC Section 501.6(B), Fuses for Class 1, Division 2 Locations3.17.1 NEC Section 517.17, Requirements for Ground-Fault Protection and

Coordination in Health Care Facilities3.18.1 NEC Section 520.53(F)(2), Protection of Portable Switchboards on Stage3.19.1 NEC Section 550.6(B), Overcurrent Protection Requirements for Mobile

Homes and Parks3.20.1 NEC Section 610.14(C), Conductor Sizes and Protection for Cranes and

Hoists3.21.1 NEC Section 620.62, Selective Coordination of Overcurrent Protective

Devices for Elevators3.22.1 NEC Section 670.3, Industrial Machinery3.23.1 NEC Section 700.5, Emergency Systems: Their Capacity and Rating3.23.2 NEC Section 700.16, Emergency Illumination3.23.3 NEC Section 700.25, Emergency System Overcurrent Protection

Requirements (FPN)3.24.1 NEC Section 705.16, Interconnected Electric Power Production Sources:

Interrupting and Short-Circuit Current Rating3.25.1 NEC Section 725.23, Overcurrent Protection for Class 1 Circuits3.26.1 NEC Section 760.23, Requirements for Non-Power-Limited Fire Alarm

Signaling Circuits

3.1.0 Introduction

In this section, a presentation format of questions and answers has been used tofocus on the factors that are pertinent to a basic understanding and application ofovercurrent 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 compliancewith the NEC. The following is by permission of Cooper Bussmann, Inc.

3.1.1 NEC Section 90.2, Scope of the NEC

3.2.1 NEC Section 110.3(A)(5), (6), and (8)Requirements for Equipment Selection

3.1.1

3.2.1

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3.2.2 NEC Section 110.3(B), Requirements forProper Installation of Listed and Labeled Equipment

3.4 Section Three

3.2.2

(continued)

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3.2.2 (Continued )

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3.2.3 NEC Section 110.9, Requirements for ProperInterrupting Rating of Overcurrent Protective Devices

3.6 Section Three

3.2.3

(continued)

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3.2.3 (Continued)

(continued)

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3.8 Section Three

3.2.3 (Continued )

(continued)

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3.2.3 (Continued)

(continued)

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3.10 Section Three

3.2.3 (Continued)

(continued)

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3.2.3 (Continued)

(continued)

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3.12 Section Three

3.2.3 (Continued )

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3.2.4 NEC Section 110.10, Proper Protectionof System Components from Short Circuits


3.2.4

(continued)

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3.14 Section Three

3.2.4 (Continued )

(continued)

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3.2.4 (Continued )

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3.3.1 NEC Section 210.20(A), Ratings ofOvercurrent Devices on Branch Circuits ServingContinuous and Noncontinuous Loads

3.16 Section Three

3.3.1

3.4.1

3.4.1 NEC Section 215.10, Requirements forGround-Fault Protection of Equipment on Feeders

3.2.5 NEC Section 110.22, Proper Marking andIdentification of Disconnecting Means

3.2.5

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3.5.1

3.5.1 NEC Section 230.82, Equipment Allowed to BeConnected on the Line Side of the Service Disconnect

3.5.2 NEC Section 230.95, Ground-FaultProtection for Services

3.5.2

(continued)

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3.6.1 NEC Section 240.1, Scope ofArticle 240 on Overcurrent Protection

3.18 Section Three

3.5.2 (Continued )

3.6.1

(continued)

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3.6.2

3.6.1 (Continued )

3.6.2 NEC Section 240.3, Protection of ConductorsOther than Flexible Cords and Fixture Wires

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3.6.3 NEC Section 240.4, Proper Protection ofFixture Wires and Flexible Cords

3.20 Section Three

3.6.3

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3.6.4 NEC Section 240.6, Standard Ampere Ratings


3.6.4

3.6.5

3.6.6

3.6.5 NEC Sections 240.8 and 380.17, ProtectiveDevices Used in Parallel

3.6.6 NEC Section 240.9, Thermal Devices

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3.6.7 NEC Section 240.10, Requirements for Supplementary Overcurrent Protection

3.22 Section Three

3.6.7

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3.6.8

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.)

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overcurrent protection

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