Electrical Safety and Overcurrent Protection

Transcription

1 Electrical Safety and Overcurrent Protection Dave Vallier DSE Bussmann division Contact info: Phone:

2 Agenda 1. Electrical hazards overview 2. The role of the overcurrent protective device 3. Arc-flash mitigation Safety by design Maintenance considerations 2

3 What are the hazards? 3

4 Electrical hazards overview Shock Arc-flash Heat Fire Arc-blast Pressure Shrapnel Sound 4

5 Electric shock hazards 70E Article 100 Definition Shock Hazard. A source of possible injury to health associated with current through the body caused by contact or approach to energized electrical conductors or circuit parts. Informational Note: Injury and damage to health resulting from shock is dependent on the magnitude of the electrical current, the power source frequency (e.g., 60 Hz, 50 Hz, dc), and the path and time duration of current through the body. The physiological reaction ranges from perception, muscular contractions, inability to let go, ventricular fibrillation, tissue burns, and death. Shock boundaries 5

6 NFPA 70E Electrical Shock Boundaries Table 130.4(D)(a) Open Side Of Enclosure Limited Space Enclosure Restricted Space Exposed Energized Conductor or Circuit Part 2015 Eaton. All Rights Reserved.. Limited Approach Boundary (Shock) Zero Distance Restricted Approach Boundary (Shock) 6

7 Electric arc 35,000 F Radiant heat Molten metal Pressure waves Copper Vapor: Expands from solid to vapor 67,000 times Sound waves Shrapnel Rapid hot air expansion Intense light 7

8 Hazards associated with arc-flash and arc-blast Heat burns & ignition of material Arc temperature of 35,000 o F Molten metal, copper vapor, heated air Second degree burn threshold: 80 o C / 175 o F (0.1 sec), 2 nd degree burn Third degree burn threshold: 96 o C / 205 o F (0.1 sec), 3 rd degree burn Intense light Pressures from expansion of metals & air Eardrum rupture threshold: 720 lbs/ft 2 Lung damage threshold: lbs/ft 2 Shrapnel Flung across room or from ladder/bucket Eye damage, cataracts 8

9 The role of the overcurrent protective device 9

10 The role of the overcurrent protective device Flash protection boundaries and incident energy exposure levels both depend upon: Duration of arc-fault or time to clear Related to speed of the OCPD Arc-fault current magnitude Related to available fault current Current-limitation can reduce 10

11 IEEE/PCIC staged arc-flash tests Ad-hoc safety committee Users Consultants Manufactures Medical examiners IEEE paper published March

12 Test 4: 640A non-current limiting device 22.6 ka available fault current 480 V, 3 phase 640 A OCPD Non-current limiting 6 cycle short time delay Fault initiated on line side of 30 A fuse 30 A RK1 current limiting fuse NEMA size 1 starter 12

13 Test 4 still photos 13

14 Test 4 results Feeder OCPD provided protection 640 A w/ STD Opened in 6 cycles Non-current limiting Incident energy: 5.8 cal/cm 18 Sound: T2: >225 o C/437 o F Pressure: >2160 lbs/ft 2 T3: 50 o C/122 o F T1: >225 o C/437 o F > Indicates meter pegged 14

15 Test 3: 601A current limiting Class L fuse 22.6 ka available fault current 480 V, 3 phase 601 A OCPD Current limiting Class L fuse Fault initiated on line side of 30 A fuse 30 A RK1 current limiting fuse NEMA size 1 starter 15

16 Test 3 still photos 16

17 Test 3 results Feeder OCPD provided protection 601 A Class L fuse Opened in less than ½ cycle Current limiting Incident energy: 1.6 cal/cm 18 Sound: T2: 62 o C/143.6 o F Pressure: 504 lbs/ft 2 T3: no change T1: >175 o C/347 o F > Indicates meter pegged 17

18 Test 1: 30A current limiting Class CC fuse 601 A OCPD Current limiting Class L fuse 22.6 ka available fault current 480 V, 3 phase 30 A RK1 current limiting fuse NEMA size 1 starter Fault initiated on load side of 30 A fuse 18

19 Test 1 still photos 19

20 Test 1 results Branch OCPD provided protection 30 A Class CC fuse Opened in less than ½ cycle Current limiting Incident energy: < 0.25 cal/cm 18 Sound: no change T2: no change Pressure: no change T3: no change T1: no change Note actual hazard based on feeder device 20

21 Comparison of test results Test 4 Test 3 Test 1 Non-current limiting AFB = 47, I.E. = 5.8 cal/cm 2 Current limiting AFB = 22, I.E. = 1.6 cal/cm 2 Current limiting AFB = 6, I.E. = <0.25 cal/cm 2 21

22 Incident energy table for fuses Based on IEEE testing of Bussmann series Low-Peak fuses 22

23 Arc-flash mitigation: Safety by design 23

24 Safety by design 70E Article 110 Requirement 110.1(H)(3) Hierarchy of Risk Control Methods. The risk assessment procedure shall require that preventive and protective risk control methods be implemented in accordance with the following hierarchy: (1) Elimination (2) Substitution (3) Engineering controls (4) Awareness (5) Administrative controls (6) PPE Engineering controls On of the three most effective methods to reduce hazards Applied at the source of possible injury not affected by human error Sound engineering design for safety can greatly reduce hazards 24

25 Current limitation = arc energy reduction Test 4 Test 3 Test 1 6 cycle clearing 1/2 cycle clearing 1/4 cycle clearing Current-limitation can significantly reduce arc energy 25

26 Current limitation effects Various level of current limitation based on fuse type and class 26

27 Upgrade to Bussmann series Low-Peak fuses Class RK1 Dual element time delay Renewable Class RK1 Non-time delay Class H/K5 Class RK5 Time delay 27

28 Specify finger-safe fusible panelboards UL 98 disconnect with CUBEFuse branch circuits Service branch fuses without opening trim Fuse rejection, interlock, and indication Door-in-door construction 28

29 Minimize shock hazards: Finger-safe solutions 29

30 Minimize shock hazards: Barriers Add barriers to prevent shock when replacing fuses New requirement for lineside barriers in service entrance equipment Deadfront barriers prevent access to live parts 30

31 Add local disconnects Increase likelihood that work will be performed in electrically safe state Ability to size current-limiting fuses close to the load and possibly reduce arc flash hazards UL 98 disconnects can be used as branch disconnect, motor controller disconnect or within sight motor disconnect 31

32 Arc-flash protecting OCPD Upstream OCPD in separate enclosure Protecting OCPD Upstream in separate enclosure Incident energy levels at equipment to be serviced depend on upstream OCPD Utilize current-limiting OCPDs as the arc flash protecting device Downstream equipment to be serviced 32

33 Arc-flash reduction maintenance switch Utilize electronic trip units to reduce the opening time When enabled, ARMS places circuit into maintenance mode while work is performed Eaton s Arc Energy Reduction System is the fastest offering for incident energy reduction with circuit breakers 33

34 Arc-flash mitigation: maintenance considerations 34

35 NFPA 70E condition of maintenance 70E Article 100 Definition Maintenance, Condition of. The state of the electrical equipment considering the manufacturers instructions, manufacturers recommendations, and applicable industry codes, standards, and recommended practices. 70E 90.2 Scope (A) Covered. This standard addresses electrical safetyrelated work practices, safety-related maintenance requirements, and other administrative controls for employee workplaces that are necessary for the practical safeguarding of employees relative to the hazards associated with electrical energy... Direct relationship between maintaining electrical equipment and safety Maintenance is not just an overhead cost part of overall safety program 35

36 Condition of maintenance two types 70E Article 110 Requirement 110.1(C) Condition of Maintenance. The electrical safety program shall include elements that consider condition of maintenance of electrical equipment and systems. Protecting OCPD Condition of maintenance: Provide arc flash mitigation as specified Must consider maintenance of protecting OCPD and the equipment to be serviced Condition of both play major role in the safety of the system Downstream equipment to be serviced Condition of maintenance of equipment to serviced 36

37 General maintenance requirements 70E Article 205 Requirement General Maintenance Requirements. Electrical equipment shall be maintained in accordance with manufacturers instruction or industry consensus standards to reduce the risk associated with failure. The equipment owner or the owner s designated representative shall be responsible for maintenance of the electrical equipment and documentation. Recommend decal system for testing and maintenence 70E Article 205 Requirement Overcurrent Protective Devices. Overcurrent protective devices shall be maintained in accordance with the manufacturers instruction or industry consensus standards. Maintenance, tests and inspections shall be documented. 37

38 Overcurrent protective device maintenance 70E Article 210 Requirement Protective Devices. Protective devices shall be maintained to adequately withstand or interrupt available fault current. Informational Note: Improper or inadequate maintenance can result in increased opening time of the overcurrent protective device, thus increasing incident energy. 70E Article 225 Requirements Fuses. Fuses shall be maintained free of breaks or cracks in fuse cases, ferrules, and insulators. Fuse clips shall be maintained to provide adequate contact with fuses. Fuseholders for current-limiting fuses shall not be modified to allow the insertion of fuses that are not current-limiting. Non-current limiting fuses shall not be modified to allow their insertion into current limiting fuseholders Molded-Case Circuit Breakers. Molded-case circuit breakers shall be maintained free of cracks and cracked or broken operating handles Circuit Breaker Testing After Electrical Faults. Circuit breakers that interrupt faults approaching their interrupting rations shall be inspected and tested in accordance wit the manufacturer s instructions. 38

39 OCPD maintenance affects safety Theoretical calculated values 800 A OCPD 6 cycle opening for arcing current Actual values due to poor maintenance 800 A OCPD 30 cycle opening for arcing current 22.6 ka Sym. available fault current 480 V, 3 phase 22.6 ka Sym. available fault current 480 V, 3 phase Panel Panel Initial calculated values: Incident energy: 5.8 cal/cm 18 Arc flash boundary: 47 Actual calculated values: Incident energy: 29 cal/cm 18 Arc flash boundary:

40 Resetting circuit breakers and replacing fuses 70E Article 130 Requirement 130.6(M) Reclosing Circuits After Protective Device Operation. After a circuit is de-energized by the automatic operation of a circuit protective device, the circuit shall not be manually reenergized until it has been determined that the equipment and circuit can be safely energized. The repetitive manual reclosing of circuit breakers or re-energizing circuits through replaced fuses shall be prohibited. When it is determined from the design of the circuit and the overcurrent devices involved that the automatic operation of a device was caused by an overload rather than a fault condition, examination of the circuit or connected equipment shall not be required before the circuit is re-energized. Cannot reset circuit breaker without identifying the cause Must determine it is safe to reenergize Examination not required for overloads Similar requirements found in OSHA (b)(2) 40

41 Reducing electrical hazards Design phase Use engineering controls and Safety by Design Specify current limiting OCPDs and touch-safe products Existing equipment Do not work energized Maintain equipment, especially OCPDs Change out non-current limiting OCPDs to current-limiting Utilize Low-Peak fuses 41

42 Additional resources and tools Fault current calculator FC2 Available in the app store or play store Fuseology Technical Guide SPD Electrical Protection Handbook Section 5: Maintenance Section 6: Electrical safe work practices 42

43 Specify touch-safe, current-limiting Low-Peak fuses to increase safety, reduce risk and improve protection. 43

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