Suggestion on How to Use Industry Trainers are

Interrupting Rating © 2015 Eaton. All Rights Reserved. .

Interrupting Rating • NEC Article 100 defines interrupting rating: • The highest current at

Interrupting Rating • NEC 110. 9 • Equipment intended to interrupt current at fault

Interrupting Rating • OCPD with improper Interrupting Rating 10, 000 A IR, 600 V,

Interrupting Rating • OCPD with improper Interrupting Rating 14, 000 A IR, 480 V,

Interrupting Rating • Marking the Interrupting Rating of OCPDs • NEC 240. 60(C) requires

Interrupting Rating - Fuses • Modern current-limiting fuses typically have a minimum interrupting rating

Proper Application 50, 000 Amperes Class J, 20 A Time-Delay Fuse 300, 000 A.

Proper Application Before After Fuses: 300, 000 A. I. R. © 2015 Eaton. All

Interrupting Rating - MCCB • Circuit breakers can be rated in various increments between

Interrupting Rating - Example • What Interrupting Rating must the fuse have? • At

Interrupting Rating - Example • What Interrupting Rating must the CB have? • Some

Interrupting Rating • The interrupting rating shown on the label for a 3 pole

Single Pole Interrupting Capabilities • A circuit breaker’s ability to safely open an overcurrent

UL 489 Table 7. 1. 7. 2 Frame Rating 240 V 480/277 V 480

Single Pole Interrupting Capability UL 489 Circuit Breaker Procedure UL Single Pole Short-Circuit Test

2002 ® NEC Change 240. 85 FPN: Proper application of molded case circuit breakers

Ground Fault Current Path 277 V SERVICE PANEL C A 2 Fault to Conduit

Solidly Grounded WYE System SERVICE PANEL BRANCH PANEL 277 V Steel Conduit C A

Solidly Grounded WYE System Single Pole Must SERVICE BRANCH Interrupt Fault Current PANEL 277

Other System Types • Corner Grounded Delta Systems (solidly grounded) • Resistance Grounded System

Corner Grounded Delta System SERVICE PANEL BRANCH PANEL Steel Conduit A 480 V V

Corner Grounded Delta System Single Pole Must Interrupt Fault Current SERVICE BRANCH PANEL Steel

High Resistance Grounded System SERVICE PANEL Resistor BRANCH PANEL 277 V Steel Conduit C

High Resistance Grounded System 277 V Resistor Keeps First SERVICE Fault Current Low: PANEL

High Resistance Grounded System Single Pole Must SERVICE BRANCH Interrupt Fault Current PANEL 277

Ungrounded System SERVICE PANEL BRANCH PANEL Steel Conduit A A 480 V C B

Ungrounded System Single Pole Must SERVICE BRANCH Interrupt Fault Current PANEL Steel Conduit A

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Suggestion on How to Use • Industry Trainers are encouraged to use this material in their sessions • Download the presentation file • Print the Notes pages and read them as you view the presentation in the “Slide Show” view. In this way you see the slides in large format and have animation (when available) © 2015 Eaton. All Rights Reserved. . 1

Interrupting Rating • NEC Article 100 defines interrupting rating: • The highest current at rated voltage that a device is identified to interrupt under standard test conditions. © 2015 Eaton. All Rights Reserved. . 3

Interrupting Rating • NEC 110. 9 • Equipment intended to interrupt current at fault levels shall have an interrupting rating at nominal circuit voltage sufficient for the current that is available at the line terminals of the equipment. • Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage sufficient for the current that must be interrupted. • The interrupting rating of the OCPD must be equal to or greater than the short-circuit current available or… © 2015 Eaton. All Rights Reserved. . 4

Interrupting Rating • Marking the Interrupting Rating of OCPDs • NEC 240. 60(C) requires marking the interrupting rating of branch-circuit cartridge fuses if other than 10, 000 A. • NEC 240. 83(C) requires marking the interrupting rating of branch-circuit breakers if other than 5, 000 A. • Does not apply to supplemental protective devices (glass tube fuses or supplementary protectors). © 2015 Eaton. All Rights Reserved. . 19

Interrupting Rating - MCCB • Circuit breakers can be rated in various increments between 5, 000 A and 200, 000 A. • Circuit breaker interrupting rating is dependent upon voltage. • Interrupting rating at 240 V may equal 65, 000 A. However, the same circuit breaker may have an interrupting rating at 480 V of 35, 000 A. © 2015 Eaton. All Rights Reserved. . 23

Interrupting Rating - Example • What Interrupting Rating must the fuse have? • At least 50, 000 amperes. (Class R, J, T, L and CC fuses have an Interrupting Rating of at least 200, 000 amperes. • The short-circuit current rating of the switch may also be 200, 000 amperes. © 2015 Eaton. All Rights Reserved. . 24

Interrupting Rating - Example • What Interrupting Rating must the CB have? • Some value greater than or equal to 50, 000 amperes. • The interrupting rating for a circuit breaker is dependent upon voltage. • Circuit breakers come in a wide variety of interrupting ratings – If the choices are 14, 000 A, 25, 000 A or 65, 000 A – a 65, 000 A circuit breaker would need to be selected for the circuit shown. © 2015 Eaton. All Rights Reserved. . 25

Interrupting Rating • The interrupting rating shown on the label for a 3 pole circuit breaker is based upon the three phase bolted fault test which has all three phase conductors connected electrically together. © 2015 Eaton. All Rights Reserved. . 26

Single Pole Interrupting Capabilities • A circuit breaker’s ability to safely open an overcurrent at a specified voltage utilizing only one pole of the circuit breaker is the single pole interrupting capability • A circuit breaker’s single pole interrupting capability is typically lower than its multi-pole interrupting rating. © 2015 Eaton. All Rights Reserved. . 27

UL 489 Table 7. 1. 7. 2 Frame Rating 240 V 480/277 V 480 V 600/347 V 600 V 100 A Maximum 250 V Maximum 4, 330 -- -- 100 A Maximum 251 -600 V -- 10, 000 8, 660 101 -800 A 8, 660 10, 000 8, 660 801 -1200 A 12, 120 14, 000 12, 1201 -2000 A 14, 000 14, 000 2001 -2500 A 20, 000 20, 000 2501 -3000 A 25, 000 25, 000 3001 -4000 A 30, 000 30, 000 4001 -5000 A 40, 000 40, 000 5001 -6000 A 50, 000 50, 000 28 © 2015 Eaton. All Rights Reserved. .

Single Pole Interrupting Capability UL 489 Circuit Breaker Procedure UL Single Pole Short-Circuit Test CB Frame Rating 100 A Maximum 101 – 800 A. 480/277 V 480 V 10, 000 Amps 8, 660 Amps © 2015 Eaton. All Rights Reserved. . 29

2002 ® NEC Change 240. 85 FPN: Proper application of molded case circuit breakers on 3 -phase systems, other than solidly grounded wye, particularly on corner grounded delta systems, considers the circuit breakers’ individual pole interrupting capability. Reprinted from NEC® 2002 © 2015 Eaton. All Rights Reserved. . 31

Solidly Grounded WYE System Single Pole Must SERVICE BRANCH Interrupt Fault Current PANEL 277 V Steel Conduit C A 480 V 27 V 77 2 A 7 V B B 480 V Fault to Conduit C N N © 2015 Eaton. All Rights Reserved. . 34

High Resistance Grounded System 277 V Resistor Keeps First SERVICE Fault Current Low: PANEL 5 Amps or So C A Steel Conduit A 27 7 V 27 BRANCH PANEL 7 V B 480 V C © 2015 Eaton. All Rights Reserved. . First Fault to Steel Conduit 39

High Resistance Grounded System Single Pole Must SERVICE BRANCH Interrupt Fault Current PANEL 277 V Steel Conduit C A A 27 7 V B 480 V C High Value of Fault Current Because Ground Resistor No Longer in Path Second Fault to Enclosure © 2015 Eaton. All Rights Reserved. . First Fault to Steel Conduit Takes Path of Least Resistance 40

Ungrounded System SERVICE PANEL BRANCH PANEL Steel Conduit A A 480 V C B B 480 V C First Fault to Steel Conduit Low Value of Fault Current Because of Large Capacitively Coupled Impedance to Ground © 2015 Eaton. All Rights Reserved. . 42

Ungrounded System Single Pole Must SERVICE BRANCH Interrupt Fault Current PANEL Steel Conduit A A 480 V C B B 480 V High Value of Fault Current Because Large Impedance is No Longer in Path C Second Fault to Enclosure © 2015 Eaton. All Rights Reserved. . First Fault to Steel Conduit Takes Path of Least Resistance 43