NATIONAL ELECTRIC SAFETY CODE (ANSI C2 / NESC)
NATIONAL ELECTRICSAFETY CODE(ANSI C2 / NESC)Jim TomaseskiIBEW Director of Safety and Health
NESC 2012 Executive Subcommittee approved finaldraft – April 1, 2011 2012 Edition published on August 1, 2011 Effective January 1, 2012
NESCCOMMITTEE STRUCTURE Chairman and Vice Chairman Main Committee Executive Committee Interpretations Subcommittee Interim Amendment SubcommitteeSubcommittee 1 – Purpose, Scope, Application,Definitions, and ReferenceSubcommittee 2 – Grounding MethodsSubcommittee 3 – Electric Supply StationsSubcommittee 4 – Overhead Lines – ClearancesSubcommittee 5 – Overhead Lines – Strength and LoadingSubcommittee 7 – Underground LinesSubcommittee 8 – Work Rules
NESCSection 1 – Introduction (Scope, Purpose)Section 2 – DefinitionsSection 3 – ReferencesSection 9 – Grounding Methods
NESC Part 1 – Rules for the Installation of Electric SupplyStations and EquipmentPart 4 Part 2 – Safety Rules for the Installation andMaintenance of Overhead Electric Supply andCommunication LinesWork Rules for the Operationof Electric Supply and Part 3 – Safety Rules for the Installation andCommunicationsLinesandMaintenanceof Underground ElectricSupplyandCommunication LinesEquipment Part 4 – Work Rules for the Operation of ElectricSupply and Communications Lines and EquipmentSubcommittee 8– Appendix A – Uniform System of Clearances– Appendix B - Uniform clearance calculations for conductorsunder ice and wind conditions
NESC (2007) SCOPE 011. ScopeA. These rules cover supply and communicationlines, equipment, and associated work practicesemployed by a public or private electric supply,communications, railway, or similar utility in theexercise of its function as a utility. They coversimilar systems under the control of qualifiedpersons, such as those associated with anindustrial complex or utility interactive system.
NESC (2007) SCOPEB. The NESC covers utility facilities and functions up to the servicepoint.NOTE: The National Electrical Code (NEC - NFPA 70, 2005 Edition)covers utilization wiring requirements beyond the service point.C. NESC rules cover street and area lights (supplied by underground oroverhead conductors) under the exclusive control of utilities (includingtheir authorized contractors) or other qualified persons (such as thoseassociated with an industrial complex).NOTE: Luminaires not under such exclusive control are governed bythe requirements of the NEC.D. NESC rules do not cover installations in mines, ships, railway rollingequipment, aircraft, or automotive equipment, or utilization wiringexcept as covered in Parts 1 and 3.
NEC / NFPA - oldSection 90.2(B)(5):(5) Installations under the exclusive control of an electricutility where such installationsa. Consistof serviceor servicelaterals, andArelocatedin dropslegallyestablishedassociated metering, oreasements,rights-of-way, or byb. Are located in legally established easements, rightsof-way, oragreementsby other agreementseitherdesignateddesignated by orothereitherrecognized by public service commissions, utilitybyor recognized by public servicecommissions, or other regulatory agencies havingjurisdiction for such installations,orcommissions,utility commissions,orc. Are onregulatoryproperty ownedagenciesor leased by theelectric utilityotherhavingfor the purpose of communications, metering,jurisdictionfortransformation,such installationsgeneration, control,transmission, ordistribution of electric energy.
NEC / NFPA - newChanged 90.2(B)(5) to read as follows:(5) Installations under the exclusive control of an electric utility wheresuch installationsa. Consist of service drops or service laterals, and associated metering,orb. Are on property owned or leased by the electric utility for thepurpose of communications, metering, generation, control,transformation, transmission, or distribution of electric energy, orc. Are located in legally established easements or rights-of-way, ord. Are located by other written agreements eitherdesignated by or recognized by public service commissions, utilitycommissions, or other regulatory agencies having jurisdiction forsuch installations. These written agreements shall be limited toinstallations for the purpose of communications, metering,generation, control, transformation, transmission, or distribution ofelectric energy where legally established easements or rights-of-waycannot be obtained. These installations shall be. limitedto Federal Lands, Native American Reservations through the U.S.Department of the Interior Bureau of Indian Affairs, Military bases,lands controlled by port authorities and State agencies anddepartments, and lands owned by railroads.These installations shall be limitedto Federal Lands, Native AmericanReservations through the U.S.Department of the Interior Bureau ofIndian Affairs, Military bases, landscontrolled by port authorities andState agencies and departments,and lands owned by railroads
NESC 2012 – Part 4Work Rules for the Operation of Electric Supply andCommunications Lines and Equipment Complete review to “clean up” language 2 significant changes– Rule 410.3 on arc flash Rewrite to clarify intent Inclusion of 1000 volt exposures– Minimum Approach Distances (MAD) Clean up Rule 441 Simplify MAD rules
NEW RULE 410.3 The employer shall ensure that anassessment is performed to determinepotential exposure to an electric arc foremployees who work on or near energizedlines, parts, or equipment. If the assessment determines potentialemployee exposure, clothing made fromacetate, nylon, polyester, or polypropyleneshall not be worn, unless arc rated.
NEW RULE 410.3 If the assessment determines a potential employeeexposure greater than 2 cal/cm2 exists (see Neal,Bingham, and Doughty [B59]), the employer shall:a. Perform a detailed arc hazard analysis, or use Table410- 1, 410-2, or 410-3 to determine the effective arcrating of clothing or a clothing system to be worn byemployees working on or near energized lines, parts, orequipment at voltages 50 V to 800,000 V. The arc hazardanalysis shall include a calculation of the estimated arcenergy based on the available fault current, the duration ofthe arc (cycles), and the distance from the arc to theemployee.
NEW RULE 410.3 If the assessment determines a potentialemployee exposure greater than 2 cal/cm2exists (see Neal, Bingham, and Doughty [B59]),the employer shall:b. Require employees to wear clothing or aclothing system with an effective arc rating notless than the anticipated level of arc energy.
NEW RULE 410.3EXCEPTION: If the clothing or clothing system required by this rulehas the potential to create additional or greater hazards than thepossible exposure to the heat energy of the electric arc, then clothingor a clothing system with an effective arc rating less than that requiredby the this rule may be worn.NOTE 1: Assessments performed to determine potential exposure toan electric arc consider the affected employee’s assigned tasks and/orwork activities.NOTE 2: A clothing system (multiple layers) that includes an outerlayer of flame resistant material and an inner layer of non-flameresistant natural fiber material has been shown to block more heat thana single layer. The effect of the combination of these multiple layersmay be referred to as the effective arc rating (e.g., EBT, ATPV).NOTE 3: Engineering controls can be utilized to reduce arc energylevels and work practices can be utilized to reduce exposure levels.
NESC 2012 – Rule 410.A.3WHAT DOES RULE MEANANDWHEN DOES IT APPLY?Interpretation requests (IR)asked these questions
NESC 2007 – Rule 410.A.3(IR – 557)Does this rule apply to insulated conductors in anunderground manhole location. If an employee isworking on a de-energized conductor in a manhole, doeshe need arc flash protection for the other energized, butinsulated conductors, that are located in the samemanhole.While it is theoretically possible for an arc tooccur whenever parts or equipment areenergized, the likelihood – in part – istypically dependent upon the work beingperformed on energized facilities.
NESC 2007 – Rule 410.A.3(IR – 558)Does the term “potential exposure” mean “any possibleexposure” or does it mean “an exposure with a strongpossibility of occurring?”“Potential exposure” can be interpreted as “any exposureexisting in possibility” or it can be interpreted as “an exposurewith a strong possibility” of actually occurring. After 1 January2009, these differences in interpretation almost certainly willresult in differences in application of the Rule.See I.R. 557 - Rule 410A3 requires an assessment of thepotential for an electric arc and the wearing of protectiveclothing as appropriate. The employer is responsible fordetermining potential employee exposure, based on whatactivities will occur and to what extent such activities maypotentially initiate an arc.
NESC 2012Low voltage arc exposure 1000 VoltsPROPOSED TO: Clarify interpretation issues Specifically include 1000 volt exposures Provide Table similar to existing Tables
NEW TABLE 410-1Nominal Voltage Range and Calories/Cm2Equipment Type50 – 250 V251 – 600 V601 – 1000 VSelf-contained meters /Cabinets42204308Pad-mounted transformers494968CT meters and control wiring424568Metal-clad Switchgear / MotorControl Centers83406608Pedestals, Pull Boxes, HandHoles4287128Open Air (includes lines)424768Network Protectors410Note 11Note 11Panel boards - single phase (all) /three phase ( 100 A)42812128Panel boards – three phase( 100 A)42Note 13Note 13
Footnotes To Table 410-11. This table was developed from fault testing based onequipment type and is independent of fault currentunless otherwise noted.Calculations and test data are based on an 18 inseparation distance from the arc to the employee. SeeIEEE Std 1584-2002.Other methods are available to estimate arc exposurevalues and may yield slightly different but equallyacceptable results.The use of the table in the selection of clothing isintended to reduce the amount or degree of injury butmay not prevent all burns.
Footnotes To Table 410-12. Industry testing on this equipment by two separate majorutilities and a research institute has demonstrated thatvoltages 50 V to 250 V will not sustain arcs for more than2 cycles, thereby limiting exposure to less than 4 cal/cm2.3. Value based on IEEE 1584 formula for Motor ControlCenters. (Gap 1 in) (Xd 1.641) (18 in distance) 51 kA(Based on a 208 V, 1000 kVA, 5.3% Z, served from a 500MVA system) Maximum duration without circuitprotective device operation from industry testing (see Ref[1]) is 10 cycles: 46.5 cal/s/cm2 x 0.167 s 7.8 cal/cm2.4. Industry testing on 480 V equipment indicates exposuresfor self-contained meters do not exceed 20 cal/cm2.5. Industry testing on 480 V equipment indicates exposuresfor CT meters and control wiring does not exceed 4cal/cm2.
Footnotes To Table 410-16. Value based on IEEE 1584 formula for Motor Control Centers.(Gap 1 in) (Xd 1.641) (18 in distance) 12.7 kA at 480 V (worstcase energy value from testing). (See Ref [2].) Maximumduration without circuit protective device operation from tests is85 cycles: 26.2 cal/s/cm2 x 1.42 s 37 cal/cm2.7. Incident analysis on this equipment indicates exposures do notexceed the values in the table.8. Engineering analysis indicates that applying a 150% multiplierto the 480 V exposure values provides a conservative value forequipment and open air lines operating at 601 V to 1000 V.9. Industry testing on 480 V equipment indicates exposures onpad-mounted transformers do not exceed 4 cal/cm2. (See Ref[2].)10. Industry testing on 208 V network protectors indicatesexposures do not exceed 4 cal/cm2. (See Ref [1].)
Footnotes To Table 410-111. Industry testing on 480 V network protectors indicatesarcs will not self-extinguish and heat flux rates will exceed60 cal/cm2/s at 24 in working distance. Perform arc hazardanalysis. (See Ref [2].)12. Industry testing on 480 V panels with non-edge mountedbus bars indicates exposures do not exceed 8 cal/cm2.(See Ref [2].)13. Industry testing on panelboards with edge-mounted,parallel bus bars indicate arcs will not self-extinguish andheat flux rates will exceed 60 cal/cm2/s at 18 in workingdistance. Perform arc hazard analysis. (See Ref [2].)14. IEEE 1584 original test data indicates there is nosignificant difference between heat flux rates for 400 Vclass equipment verses 600 V class equipment.
Minimum Approach Distance(MAD)
Minimum Approach Distance(MAD) OSHA - in 1910.269 and 1926 Subpart V(and others) NESC - in Part 4 - Rules for the Operationof Electric Supply and CommunicationLines and equipment IEEE 516 - IEEE Guide for MaintenanceMethods on Energized Power Lines
Minimum Approach Distance(MAD) OSHA – the closest distance an employee ispermitted to approach an energized or agrounded object NESC – the closest distance a qualifiedemployee is permitted to approach either anenergized or a grounded object, asapplicable for the work method being used IEEE 516 - the minimum air insulationdistance (MAID) plus a factor for inadvertentmovement
Minimum Approach Distance(MAD) In NESC since early 1900’s Recent years based on IEEE 516calculation method IEEE 516 repeatedly changed sinceinception NESC has followed those changes IEEE 516 2009 changes begs thequestion “Why change again?”
NESC - 1914OPERATINGVOLTAGEDISTANCE INFEET750 – 7500 .6 inches7500 .115000 .250000 .370000 .5Distances for intermediate voltages to be determined byinterpolation
Minimum Approach Distance(MAD) Error discovered in phase-to-phasecalculations Phase-to-ground air saturation factorused to calculate phase-to-phase MAD Discovered error deemed some OSHAand NESC MAD values incorrect Must correct in OSHA and 2012 editionof the NESC
Minimum Approach Distance(MAD) Most significant changes occur inphase-to-phase voltages above 230 kV Phase-to-phase increases perceived asproblems by some SC8 members Distribution voltage levels also revised Are users/can users calculate TOV Engineering analysis of system iscritical to application of MAD
IEEE 516MINIMUM APPROACH DISTANCE MAIDMINIMUM AIRINSULATIONDISTANCEMAID – Minimum air insulation distanceMTID – Minimum tool insulation distanceMAD – Minimum approach distanceMAD for tools – MAD with tool in air gapMHAD – Minimum helicopter approachdistance
IEEE 516MINIMUM APPROACH DISTANCEWhat is MAD? Safe working distance Equal to the MAID Inadvertent movementfactor (worker movement) 72.5 kV 1 foot 72.5 kV 2 feet Different voltages – different equations Add a tool and add a factor Add a helicopter and add a factor
CALCULATING MADLine-to-ground and line-to-line voltages above 750 V and below 5.0 kVWhen the line-to-ground and line-to-line voltage is between750 V and 5.0 kV, sufficient test data are not available tocalculate the MAID, which is less than 2 cm or 0.07 feet.This guide recommends the following:a) MAID, line-to-ground and line-to-line1) DM 0.022) DFT 0.07b) MAD, line-to-ground and line-to-line1) DM 0.632) DFT 2.07
CALCULATING MADLine to ground above 72.5 kV DMAD ((C1) a)(VL G )(T )( A)) M DMADforTools (((C1)( C2) a)(VL G)(T)(A)) M DMHAD (((C1) a)(VL G )(T )( A)) M )(H) C1 60 Hz rod gap withstandC2 tool factor (tool in air gap)a air saturation factorVL-G line to ground voltageT maximum anticipated per-unit TOVA altitude correction factorM inadvertant movement factorH helicopter factor
CALCULATING MADTOVPeak equal to or greater than 27.00 kV – MAD Line-to-ground
CALCULATING MADMAD, line-to-line, for line-to-line voltages equal to and less than 242 kVMAD, line-to-line, for line-to-line voltages greater than 242 kV
EXAMPLE OFMAD TABLE 2007 NESCT p.u.)Line-to-ground workLine-to-line workMADMAID (ft)MTID (ft)MAD (ft)for Tools (ft)MHID (ft)MAID (ft)MAD (ft)MHID 6.533.52.943.233.944.234.335.096.096.70
Voltage inkilovoltsphase-tophase1,2,3Distance to (m)(ft-in )0 to 0.050Not specifiedNot specified0.051 to 0.300Avoid contactAvoid contact0.301 to 0.7500.321-10.321–10.751 to 150.642–20.672-315.1 to 36.00.732-50.842 - 1036.1 to 46.00.792-70.943-146.1 to 72.50.893–01.153-9Distance to employee from energized part4,5,6,10Voltage -in)72.6 to 1210.943–11.013–41.374–7121.1 to 1451.073–71.153 – 101.625–4145.1 to 1691.203 – 111.294–31.886–3169.1 to 2421.585–31.715–82.779–2242.1 to 3622.568–52.759–14.3214 – 3362.1 to 5503.3811 – 13.6111 – 116.0119 – 9550.1 to 8004.5414 - 114.8215 - 108.8729 - 2Without toolsphase-to-groundWith toolsphase-to-ground7,9Without toolsphase-to-phase8
MADNEW to- phase-to- phase-toground groundphase
Distance to employee from energized part4,5,6,10Voltage inkilovoltsphase-tophaseWithout toolsphase-to-groundWith toolsphase-to-ground7,9Without 0.943–11.013–41.374–71.073–71.153 – 101.625–41.203 – 111.294–31.886–3169.1 to2421.585–31.715–82.779–2242.1 to3622.568–52.759–14.3214 – 3362.1 to5503.3811 – 13.6111 – 116.0119 – 9550.1 to8004.5414 - 114.8215 - 108.8729 - 272.6 to 121121.1 to145145.1 to169
MADNEW TERMINOLOGYHow MAD is affectedVoltage inkilovoltsphase-to-phaseWithout toolsWith toolsphase-to-ground phase-to-ground230 kV5–35–8345 kV8–59–1500 kV11 – 111 - 11
NESC 2012MINIMUM APPROASCH DISTANCEPROPOSALSIGNIFICANT NEW FOOTNOTES Distances for live-line tools in the air gap werecalculated by adding a tool factor to the electricalcomponent (IEEE 516 C2 1.1 tool factor). Phase-to-phase live-line tool in the air gapvalues are not available. If this situation exists,an engineering evaluation should be performed. With tools means a live-line tool bridging the airgap to the employee from the energized part.
MINIMUM APPROACH DISTANCESWHAT’S IN THE FUTURE OSHA 1926 Subpart V and 1910.269MAD tables are incorrect OSHA re-opened rulemaking record tospecifically address MAD NESC not completed when recordclosed - IEEE 516 was OSHA should adopt 516 concepts anddistances IEEE and IEC being revised
C. NESC rules cover street and area lights (supplied by underground or overhead conductors) under the exclusive control of utilities (including their authorized contractors) or other qualified persons (such as those associated with an industrial complex). NOTE: Luminaires not under such exclusive control are governed by the requirements of the NEC.
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ANSI/BHMA certified A156.2-2011 Exceeds 400,000 ANSI cycles Medium traffic ANSI/BHMA certified A156.5-2010 Exceeds 150,000/250,000 ANSI cycles High traffic, heavy-duty ANSI/BHMA certified A156.2-2011 Exceeds 1,000,000 ANSI cycles High traffic ANSI/BHMA certified A156.2-2011 Exceeds 1,000,000 ANSI cycles He
