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 Component Protection © 2015 Eaton. All Rights Reserved.. Component Protection • Electrical system components must be applied within their short-circuit current ratings. • Electrical system components can be destroyed if the overcurrent devices do not limit the short-circuit current to within the short-circuit current rating of the system’s components. • NEC 110.10 covers protection of electrical system components. © 2015 Eaton. All Rights Reserved.. 3 Component Protection • NEC 110.10 – Circuit Impedance, Short-Circuit Current Ratings, and Other Characteristics. • “The overcurrent protective devices, the total impedance, the equipment short-circuit current ratings, and other characteristics of the circuit to be protected shall be so selected and coordinated to permit the circuit protective devices used to clear a fault to do so without extensive damage to the electrical equipment of the circuit.” • The specified OCPD must protect the electrical components/equipment from damage under short circuit conditions. © 2015 Eaton. All Rights Reserved.. 4 Component Protection • NEC 110.10 – Circuit Impedance, Short-Circuit Current Ratings, and Other Characteristics. • “This fault shall be assumed to be either between two or more of the circuit conductors or between any circuit conductor and the equipment grounding conductor(s) permitted in 250.118.” • The equipment must be protected for the various types of potential faults, including phase to phase, phase-to-ground, phase-to-neutral © 2015 Eaton. All Rights Reserved.. 5 Component Protection • NEC 110.10 - Component Protection • “Listed equipment applied in accordance with their listing shall be considered to meet the requirements of this section.” • The testing requirements of electrical components must be understood to assure proper application and protection. © 2015 Eaton. All Rights Reserved.. 6 Component Protection • Component short-circuit current ratings depends upon: 1) Amount of fault current (RMS sym. short-circuit current, and in some cases, peak let-through current) and length of time, or 2) I2t Withstand Ratings • These values have been established through short-circuit testing of the components. • If both the let-through currents (IRMS and Ip) and the time it takes to clear the fault, or the let-through I2t, of the currentlimiting overcurrent protective device are less than the withstand rating of the electrical component, then that component will be protected from short-circuit damage. © 2015 Eaton. All Rights Reserved.. 7 Component Protection • The following components can be analyzed by establishing the short-circuit withstand data of each component and then selecting the proper overcurrent protective device: • Wire/Cable • Bus (Busway, Switchboards, Motor Control Centers and Panelboards) • Low Voltage Motor Controllers • Transfer Switches © 2015 Eaton. All Rights Reserved.. 8 Conductor Protection • Proper protection of conductors will improve reliability and reduce the possibility of injury. • Overcurrent devices must limit the short-circuit current to within the short-circuit current rating of the conductor. • Merely matching the ampacity rating of the conductor with the ampere rating of a protective device may not assure component protection of the conductor under short-circuit conditions, especially when the overcurrent device is sized up to 10 times the ampacity of the conductor (or even higher). © 2015 Eaton. All Rights Reserved.. 9 Conductor Protection • Withstand ratings for conductors (5 sec & I2t): • ICEA - Insulation Damage (150 Deg C) • Soares - Cable to become loose under lug (Annealing point of copper - 250 Deg C) • Onderdonk - Melting of Cable (1,083 Deg C) © 2015 Eaton. All Rights Reserved.. 10 ICEA Chart • Short Circuit Withstand Chart for Copper Conductors with Thermoplastic insulation • Allowable Short Circuit Current Based on Clearing Time and Conductor Size • Based on physics formula © 2015 Eaton. All Rights Reserved.. 11 Conductor Protection • ICEA insulation damage tables • Maximum Short Circuit Withstand Current (A) © 2015 Eaton. All Rights Reserved.. 12 Overcurrent Device Selection • The next step to analyzing protection of conductors against short circuits depends upon the overcurrent device selected and available fault current • The overcurrent protective device used to protect the conductor can either be a current limiting fuse or circuit breaker (current limiting or non-current limiting). © 2015 Eaton. All Rights Reserved.. 13 Conductor Protection 60A Class RK1 Fuse - LPS-RK60SP 40,000A RMS Sym. LOW-PEAK® Dual-Element Fuse Short-Circuit 20HP Available 460V, 3Ø 10 AWG THW Copper • The circuit shown originates at a distribution panel where 40,000 amperes RMS symmetrical are available. • The 10 AWG THW copper conductor is protected against shortcircuits by a 60A Class RK1 fuse. © 2015 Eaton. All Rights Reserved.. 14 Conductor Protection • 10 AWG conductor short circuit withstand is 4,300A for one cycle (based upon ICEA). • The OCPD (LPS-RK-60SP) must limit the 40,000A RMS fault to 4,300A and clear within one cycle or less in order to properly protect the 10AWG conductor. • The LPS-RK-60SP let-thru chart shows: that a 40,000A fault is reduced to 3,000A (w/in 1/2 cycle) • Since the amount of current let-through by the fuse is less than the short-circuit withstand for the given period of time, the conductor is protected. © 2015 Eaton. All Rights Reserved.. 15 Busway Protection KRP-C800SP 800 Amp LOW-PEAK Time-Delay Fuses Short-Circuit 65,000A RMS Sym. Available • • • 800A Switch 800 Amp Plug-in Bus Bracing Required? Available Fault current equals 65,000A With KRP-C800SP ampere LOW-PEAK® fuses, the 65,000A available fault will be reduced to 19,000 A (from the let-through charts). This would allow a standard 22,000 ampere RMS symmetrical (3-cycle) rated bus. © 2015 Eaton. All Rights Reserved.. 16 Protection of Bus • U.L. Standard 891 (Switchboards) and U.L. 67 (panelboards) detail short-circuit current ratings for a durations of 3 cycles, unless the main overcurrent device clears the short in less than three cycles. • Motor control centers, per U.L. 845 have short-circuit current ratings for a duration of 3 cycles, unless the main overcurrent device clears the short in less than 3 cycles. • Current Limiting devices can be used for protection of the bus in these assemblies. © 2015 Eaton. All Rights Reserved.. 17 Protection of Bus 800A Class L Fuses 65,000A RMS Sym. Available 800A MCC with 3 cycle 65kA Bracing 800A Power CB w/STD = 6 cycles 65,000A RMS Sym. Available 800A MCC with 3 cycle 65kA Bracing • The top design meets 110.10 of the NEC because a 65kA fault would be cleared in ½ cycle or less and the MCC is rated for 3 cycles. • The bottom design violates 110.10 because a 65kA fault could continue for 6 cycles, but the MCC is only rated for 3 cycles. © 2015 Eaton. All Rights Reserved.. 18 Motor Circuit Protection this switch, that is cleared by this protective device, With a Fault Here, M these conductors, and these motor starter contacts and O.L. relays, … must all be rated to safely withstand the energy of the fault let-through current without “extensive damage” to any of the circuit components. © 2015 Eaton. All Rights Reserved.. 19 Motor Controller Short-Circuit Current Ratings – UL 508 • UL 508 Tests motor controllers to minimum short-circuit current ratings as indicated in the table. • Higher ratings are available • At standard or higher ratings, significant, permanent damage is allowed per UL 508. © 2015 Eaton. All Rights Reserved.. 20 UL 508 - Industrial Control Equipment • Maximum Damage Criteria for Standard & High Fault Acceptance Criteria • All Devices • The door or cover shall not be blown open. • No discharge of parts beyond the enclosure. • Enclosure cannot become energized. © 2015 Eaton. All Rights Reserved.. 21 UL 508 - Industrial Control Equipment Maximum Damage Criteria for Standard & High Fault Acceptance Criteria (Cont) Motor Control Devices The load switch function of the motor control device is able to be inoperative at the conclusion of the test. The contacts of the motor control device are able to weld or completely disintegrate. Overload Relays Overload relays are allowed to be burned out. © 2015 Eaton. All Rights Reserved.. 22 Protection Levels – IEC 60947-1 & UL 508E • Type 1 • Considerable damage to the contactor and overload relay is acceptable • Replacement of components or a complete new starter may be needed • There must be no discharge of parts beyond the enclosure. • Enclosure cannot become energized. • Note: Similar to UL508 testing. © 2015 Eaton. All Rights Reserved.. 23 Protection Levels – IEC 60947-1 & UL 508E • Type 2 • No damage is allowed to either the contactor or the overload relay • Light contact welding is allowed, but must be easily separable • Testing and documentation is required to prove Type 2 Protection © 2015 Eaton. All Rights Reserved.. 24 Transfer Switch Short circuit withstand rating • Typically defined as 3-cycles at a given magnitude of current • UL1008 now allows manufacturers to optionally test for longer periods • UL1008 short circuit withstand testing only ensures that the contacts do no weld during the test • This ensures that the transfer switch can transfer to the alternate source, however, it does not ensure that the normal contacts are viable and free of damage • Because of this, the testing does not ensure that the transfer switch can be transferred back to the original source Note- Applying a transfer switch within its short circuit withstand rating does NOT guarantee that the switch survives a downstream fault without damage. © 2015 Eaton. All Rights Reserved.. 25 Transfer Switch Short time withstand rating • UL1008 allows optional testing of transfer switches to achieve a short time withstand rating • Short time ratings are also expressed in a number of cycles at a given magnitude of current. • The test for short time withstand is treated differently than the short circuit withstand • After the short time withstand test, the contacts must be viable. A temperature rise test is done to verify. Note- Applying a transfer switch within its short time withstand rating ensures the transfer switch is still completely functional after a downstream fault. © 2015 Eaton. All Rights Reserved.. 26 Transfer Switch Short circuit withstand vs. short time withstand Short circuit Short time Required by UL1008 Optional Not required by UL1008 3-cycles at rated current (65 kA, for example) Typically longer than 3-cycles Contact damage permitted Contacts must remain viable Switch not required to transfer back to normal power Ensures that switch can transfer back to normal power Manufacturer option to test at longer times © 2015 Eaton. All Rights Reserved.. 27 Transfer Switch Contactor withstand/close-on ratings UL 1008 Ampere Rating 480 V 600 V Any Breaker Specific Breaker Any Breaker Specific Breaker Fuse 40, 80, 100 10,000 30,000 10,000 22,000 100,000 150, 200 10,000 30,000 22,000 35,000 100,000 225, 260, 400 30,000 50,000 — — 200,000 40, 80, 100, 150, 200 30,000 50,000 22,000 35,000 200,000 225, 260, 400 30,000 50,000 50,000 65,000 200,000 600, 800, 1000,1200 50,000 65,000 50,000 65,000 200,000 1600 50,000 65,000 — — 200,000 © 2015 Eaton. All Rights Reserved.. 28 © 2015 Eaton. All Rights Reserved.. 29