1 © 2015 Eaton. All Rights Reserved.. 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.. Interrupting Rating

3 © 2015 Eaton. All Rights Reserved.. 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.

4 © 2015 Eaton. All Rights Reserved.. Interrupting Rating NEC 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…

5 © 2015 Eaton. All Rights Reserved.. Interrupting Rating OCPD with improper Interrupting Rating 10,000A IR, 600V, Class H Fuse 50,000 Available

6 © 2015 Eaton. All Rights Reserved.. Interrupting Rating OCPD with improper Interrupting Rating 10,000A IR, 600V, Class H Fuse 50,000 Available

7 © 2015 Eaton. All Rights Reserved.. Interrupting Rating OCPD with improper Interrupting Rating 10,000A IR, 600V, Class H Fuse 50,000 Available

8 © 2015 Eaton. All Rights Reserved.. Interrupting Rating OCPD with improper Interrupting Rating 10,000A IR, 600V, Class H Fuse 50,000 Available

9 © 2015 Eaton. All Rights Reserved.. Interrupting Rating OCPD with improper Interrupting Rating 10,000A IR, 600V, Class H Fuse 50,000 Available

10 © 2015 Eaton. All Rights Reserved.. Interrupting Rating OCPD with improper Interrupting Rating 10,000A IR, 600V, Class H Fuse 50,000 Available

11 © 2015 Eaton. All Rights Reserved.. Interrupting Rating OCPD with improper Interrupting Rating 14,000A IR, 480V, Circuit Breaker 50,000 Available

12 © 2015 Eaton. All Rights Reserved.. Interrupting Rating OCPD with improper Interrupting Rating 14,000A IR, 480V, Circuit Breaker 50,000 Available

13 © 2015 Eaton. All Rights Reserved.. Interrupting Rating OCPD with improper Interrupting Rating 14,000A IR, 480V, Circuit Breaker 50,000 Available

14 © 2015 Eaton. All Rights Reserved.. Interrupting Rating OCPD with improper Interrupting Rating 14,000A IR, 480V, Circuit Breaker 50,000 Available

15 © 2015 Eaton. All Rights Reserved.. Interrupting Rating OCPD with improper Interrupting Rating 14,000A IR, 480V, Circuit Breaker 50,000 Available

16 © 2015 Eaton. All Rights Reserved.. Interrupting Rating OCPD with improper Interrupting Rating 14,000A IR, 480V, Circuit Breaker 50,000 Available

17 © 2015 Eaton. All Rights Reserved.. Interrupting Rating OCPD with improper Interrupting Rating 14,000A IR, 480V, Circuit Breaker 50,000 Available

18 © 2015 Eaton. All Rights Reserved.. Interrupting Rating OCPD with improper Interrupting Rating 14,000A IR, 480V, Circuit Breaker 50,000 Available

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

20 © 2015 Eaton. All Rights Reserved.. Interrupting Rating - Fuses Modern current-limiting fuses typically have a minimum interrupting rating of 200,000A

21 © 2015 Eaton. All Rights Reserved.. Proper Application 50,000 Amperes Class J, 20A Time-Delay Fuse 300,000 A.I.R. Fault

22 © 2015 Eaton. All Rights Reserved.. Fuses: 300,000 A.I.R. Isca = 50,000 A BeforeAfter Proper Application

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

24 © 2015 Eaton. All Rights Reserved.. 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.

25 © 2015 Eaton. All Rights Reserved.. 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 14,000A, 25,000A or 65,000A – a 65,000A circuit breaker would need to be selected for the circuit shown.

26 © 2015 Eaton. All Rights Reserved.. 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.

27 © 2015 Eaton. All Rights Reserved.. 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.

28 © 2015 Eaton. All Rights Reserved.. Frame Rating240V480/277V480V600/347V600V 100A Maximum 250V Maximum 4, A Maximum V --10,0008,66010,0008, A 8,66010,0008,66010,0008, A 12,12014,00012,12014,00012, A 14, A 20, A 25, A 30, A 40, A 50,000 UL 489 Table

29 © 2015 Eaton. All Rights Reserved.. 8,660 Amps 10,000 Amps101 – 800 A. 10,000 Amps 100 A Maximum 480V 480/277V CB Frame Rating UL Single Pole Short-Circuit Test Single Pole Interrupting Capability UL 489 Circuit Breaker Procedure

30 © 2015 Eaton. All Rights Reserved.. Example: 20 A, 480V CB having 65,000 A.I.R. (3 Pole Test). Single pole tested at 8,660 Amps Single Pole Interrupting Capability UL 489 Circuit Breaker Procedure 8,660 Amps 10,000 Amps101 – 800 A. 10,000 Amps 100 A Maximum 480V 480/277V CB Frame Rating UL Single Pole Short-Circuit Test

31 © 2015 Eaton. All Rights Reserved 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 ® 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 ® NEC ® Change

32 © 2015 Eaton. All Rights Reserved.. B A C SERVICE PANEL BRANCH PANEL A B C N 277V N 480V Ground Fault Current Path Fault to Conduit

33 © 2015 Eaton. All Rights Reserved.. Steel Conduit B A C SERVICE PANEL BRANCH PANEL A B C N 277V N 480V Solidly Grounded WYE System

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

35 © 2015 Eaton. All Rights Reserved.. Other System Types Corner Grounded Delta Systems (solidly grounded) Resistance Grounded System Ungrounded System

36 © 2015 Eaton. All Rights Reserved.. Corner Grounded Delta System B A 480V A B C C SERVICE PANEL BRANCH PANEL Steel Conduit

37 © 2015 Eaton. All Rights Reserved.. B A 480V A B C C SERVICE PANEL BRANCH PANEL Steel Conduit Fault to Conduit Single Pole Must Interrupt Fault Current Corner Grounded Delta System

38 © 2015 Eaton. All Rights Reserved.. Resistor B A C SERVICE PANEL BRANCH PANEL A B C 277V 480V Steel Conduit High Resistance Grounded System

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

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

41 © 2015 Eaton. All Rights Reserved.. B A A B C C 480V SERVICE PANEL BRANCH PANEL Steel Conduit Ungrounded System

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

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

44 © 2015 Eaton. All Rights Reserved..