Importance of Arc Flash Analysis(Arc Flash Loss Prevention)Provides minimum requirements to prevent hazardous electrical exposures to personnel and ensure compliance with regulatory requirements applicable to electrical systems
Regulatory Requirements (elements necessary for Worker Safety)OSHA = Shall Provide Worker SafetyNFPA 70E = How to provide Worker SafetyEmployer Responsibility = ExecutionFocus on safety, promote training, use best practices
Electrical Hazards Consist of:Electric ShockArc FlashArc BlastOther Hazards
Electric ShockAn electric shock occurs when electric current passes through the body. This can happen when touching an energized part. If the electric current passes through the chest or head, death can result.
Effects of Electrical Current in the Human BodyBelow 1 milliampere: - Generally not perceptible1 milliampere: - Faint tingle5 milliamperes: - Slight shock felt; not painful but disturbing. Average individual can let go. Strong involuntary reactions can lead to other injuries.625 milliamperes (women): - Painful shock, loss of muscular control*930 milliamperes (men): - The freezing current or " let-go" range.* Individual cannot let go, but can be thrown away from the circuit if extensor muscles are stimulated.50150 milliamperes: - Extreme pain, respiratory arrest, severe muscular contractions. Death is possible.1,0004,300 milliamperes: - Rhythmic pumping action of the heart ceases. Muscular contraction and nerve damage occur; death likely.10,000 milliamperes: - Cardiac arrest, severe burns; death probable* If the extensor muscles are excited by the shock, the person may be thrown away from the power source. Source: W.B. Kouwenhoven, " Human Safety and Electric Shock," Electrical Safety Practices, Monograph, 112, Instrument Society of America, p. 93. November 1968.
Arc Flash/BlastAn arc flash (also known as arc blast) is a sudden, explosive electrical arc that results from a short circuit through air. The air in the vicinity of an arc flash is heated to between 5,000 and 35,000 degrees in no more than 1/1000 of a second, becoming an electrically-conductive plasma. The sudden heating can cause a shock wave blast equivalent to several sticks of dynamite and carrying vaporized metal and shrapnel
Safe Work PracticesOSHA 1910.333Potential for shock or other injuryWorking on or near live exposed partsPractices must be consistent with the extent of the hazardNFPA 70E 110.8Requires deenergizingRequires worker to be qualifiedRequires hazard analysisElectrical work permit
NFPA 70E Requirements for Working on or Near Live PartsPerform Arc Flash AnalysisSelect Personal Protective Equipment (PPE)Complete Energized Electrical Work PermitComplete Task Specific TrainingComplete a job briefing session
Arc Flash AnalysisEstablish Shock Protection Boundary(approach boundaries) used to reduce shock hazardConduct Flash Hazard AnalysisEstablish Flash Protection BoundaryUsed to reduce arc flash hazards and may reduce arc blast hazardsSelect Personal Protective EquipmentAnalysis per NFPA 70E requires update every 5yrs
Approach Boundary to Live PartsLimited (42 in)Restricted (12 in)Prohibited (1 in)Based on system voltage = 480VNFPA 70E, Annex C, Figure C.1.2.4
Flash Protection Boundaries (FPB)
Using NFPA 70E, the methods to determine FPBDefaults (i.e. tables)Perform Analysis that uses Calculation Methods
Levels of Exposure
Personal Protective Equipment (PPE)
PPEDesigned to protect specific areas of the bodyEye ProtectionNeck, Face, Head, ChinArm & Hand ProtectionBody ProtectionLeg & Foot Protection
PPE - GlovesVoltage rated gloves are REQUIRED for all voltage testing above 50 volts
OSHA/NFPA 70EGeneral Industry RequirementsOSHA 1910.355(a)Employees exposed to potential electrical hazards shall use protective equipment that is appropriate for the specific areas of the body to be protected and for the work to be performedNFPA 70E 130.7Provides standards for equipmentHazard Risk TablePPE MatrixExtensive detail for worker protectionProtective Equipment
OSHA FinesFor non-compliance, OSHA may audit a facility and issue finesMost recently: U.S. Postal Service$420,000 (pending) single facility
A Facilitys Electrical SystemA facilitys electrical system operates as a single, dynamic system. Its performance is dependent on the properties of each component and the loads connected to it. Many facilities expand project by project using different design and construction teams. Even though each specific project may be well planned and designed, its often the case that the area of work specific to the project is limited to only a portion of the existing electrical distribution system. In addition, due to the need for maintenance and emergency repairs, system components are often replaced with devices that are different than originally installed due to availability and cost. Because of these occurrences, its common that no one has an overall and complete understanding of the entire electrical system.
ToolsMost firms that provide arc flash services utilize specially designed software for electrical system modeling in short circuit and arc flash studies.Such as SKM Power System Tools
Process/Approach to Complete a Study
As-built DocumentationThe usual starting point is to gather all existing drawings an Owner has and sort it by location and date. (One-Line Documentation)VerificationSurvey each site and verify one-line documentation. Acquire missing info.PD types/sizes/settings, cable lengths, Xfmr impedance valuesLoadingLoad the information into SKM and run Short Circuit, Coordination, Arc Flash
Ex: How to Initiate a StudyLarge School System
Herndon HS PyramidLangley HS PyramidMcLean HS PyramidAldrin ES Churchill Road ESChesterbrook ESArmstrong ES Colvin Run ES Franklin Sherman ES
Clearview ESForestville ES Haycock ES
Dranesville ESGreat Falls ES Kent Gardens ES
Herndon ES Spring Hill ES Timber Lane ES
Hutchison ES Cooper MS Longfellow MS
Herndon MSLangley HS McLean HS
Cluster Analysis Approach
(5) field survey teams composed of (2) people each assigned to various sites within a cluster. All survey is schedule/time dependent.
CLUSTERSITESPYRAMIDS TEAMEST. TIME (mo.)
C1223A8 - 12C2283B10 - 12C3273C9 - 11C4283D10 - 12C5223E8 - 10Following C1-C5C6223A/E5 - 7C7253C9 - 11C8253B/D6 -8
1ST Step - Collect Hard Copy DataExisting Building Documents-Electrical One-Line Diagrams-Floor Plans-Maintenance Documents
2nd Step - Field Survey
Types of Equipment Surveyed
Gathering of InformationDuring Survey ProcessProtective Device Information Location, (Room/Panel/Whats it feeding?)Make, Model, ManufactureAIC and Trip Plug Rating Settings
3rd Step - Load the DataBuild SKM One-Line Diagrams for each siteVerify accuracy of informationAcquire Utility Company contribution informationRun/Review Short Circuit CalculationsThe maximum fault current can be calculated at each electrical buss in the system by knowing the properties of the power sources that will provide the current, and using the impedance values of the circuits that connect the bussesUnderstanding the Duty Rating of the equipment by comparing the available fault current to the rating of the protective device
Build the Model in the Software
Run a Short Circuit StudyCompare Protective Device Ratings Breakers/fuses Against the available 3-phase and SLG Fault currents.
Selective CoordinationIn order to be assured that all over current protection devices are coordinated, it is necessary to look at the time vs. current characteristic of each device and compare it to the characteristics of any upstream devices.
Poor CoordinationMain Breaker Trips, Shutting Down the Entire Switchboard
Adjustments to be MadeSettings
LTPU - Long time pick up
LTD Long time delay
STPU Short time Pickup
STD Short time Delay
It Short time delay bend
GFPU Ground Fault Pick up
GFD Ground Fault Delay
GFIt Ground Fault Delay bend
4th Step - Arc Flash EvaluationArc Flash EvaluationTo calculate the available arc flash energy, it is necessary to perform a short circuit study to determine the magnitude of the current that will flow in a fault condition, and also a coordination study to determine the length of time it takes for an Over Current Protection Devices (OCPD) to clear the fault.
Arc Flash Analysis
Arc Flash Analysis
5th Step Review Results/RecommendationsReports are generated based Existing (as is) conditions. Identifies the problem areas with bad coordination and high incident energy categoriesReports are generated based on Recommendations (best scenario) to better coordinate devices and lower arc flash incident energy categoriesBegin Training Process
ON-SITE ELECTRICALSAFETY TRAININGA balance of safety & technical training is essential for continuous improvementDesigned to protect lives, prevent disabling injuries, and prevent damage to your facility & equipment. Personnel learn about personal safety for working on or around electrical systemsUnderstand the proper use of materials and procedures for doing electrical workHands-on practical instruction that they can immediately apply when they go back to their workplaceWho should be trained? Anyone who