Arc Flash Calculations What Does It All Mean

Arc Flash Hazard Arc Flash Hazard Calculations – What Calculations – What

does it all mean?does it all mean?

Robert E. Fuhr, P.E.Robert E. Fuhr, P.E.

PowerStudies.comPowerStudies.com

Why are Arc Flash Hazard Why are Arc Flash Hazard Studies Needed?Studies Needed?

To Increase Electrical Safety at your To Increase Electrical Safety at your facility!facility!

Required by National Electric Code Required by National Electric Code (NEC) and OSHA(NEC) and OSHA

To Protect You!To Protect You!

OSHA RequirementsOSHA Requirements

Standard 29 CFR 1910 Subpart S, 1910 Standard 29 CFR 1910 Subpart S, 1910 to 1910.336to 1910.336

Must Must identifyidentify all all hazardshazards above 50 above 50 VoltsVolts

Must put Must put safeguardssafeguards in place for these in place for these hazardshazards

Must Must traintrain employees on safe work employees on safe work practicespractices

OSHA has officially OSHA has officially adoptedadopted NFPA 70E NFPA 70E

Employers must provide workers with Employers must provide workers with appropriate PPE as per the OSHA 29 appropriate PPE as per the OSHA 29 1910.132 (h)(1) PPE payment 1910.132 (h)(1) PPE payment requirement, i.e., (PPE) used to comply requirement, i.e., (PPE) used to comply with this part, shall be provided by the with this part, shall be provided by the employer at no cost to employees. employer at no cost to employees. Paragraph (h) became effective Paragraph (h) became effective February 13, 2008, and employers must February 13, 2008, and employers must implement the PPE payment implement the PPE payment requirements no later than May 15, requirements no later than May 15, 2008 2008

Key References in NEC ® -Key References in NEC ® -20082008

110.16 Flash Protection. 110.16 Flash Protection. Switchboards, panel boards, Switchboards, panel boards, industrial control panels, and motor industrial control panels, and motor control centers in other than dwelling control centers in other than dwelling occupancies, that are likely to require occupancies, that are likely to require examination, adjustment, servicing, examination, adjustment, servicing, or maintenanceor maintenance while while energizedenergized, , shall be field shall be field markedmarked to warn to warn qualified persons of potential electric qualified persons of potential electric arc flash hazards. arc flash hazards.

NEC 110.16 NEC 110.16 (continued)(continued)

The The markingmarking shall be located so shall be located so as to be as to be clearly visibleclearly visible to to qualified persons before qualified persons before examination, adjustment, examination, adjustment, servicing, or maintenanceservicing, or maintenance of the of the equipment. equipment.

Key References in NEC ® -Key References in NEC ® -20052005

FPN No. 1FPN No. 1 : NFPA 70E-2004, Standard : NFPA 70E-2004, Standard For Electrical Safety in the For Electrical Safety in the Workplace, Workplace, providesprovides assistanceassistance in in determining severity of potential determining severity of potential exposure, planning safe work exposure, planning safe work practices and selecting personal practices and selecting personal protective equipment. protective equipment.

NFPA 70E -Flash Hazard NFPA 70E -Flash Hazard AnalysisAnalysis

130.3 – A 130.3 – A flash hazard analysis shall be flash hazard analysis shall be donedone in order to protect personnel from in order to protect personnel from the possibility of being injured by an arc the possibility of being injured by an arc flash. flash.

The analysis shall determine:The analysis shall determine:– Flash Protection Boundary Flash Protection Boundary – Personal protective equipment Personal protective equipment

Calculate using Calculate using – Formulas in 130.3.A and Table 130.7(C)(9)Formulas in 130.3.A and Table 130.7(C)(9)

(a)(a)** in NFPA 70E in NFPA 70E– ** - Use with extreme caution!!!- Use with extreme caution!!! – Equations in IEEE 1584Equations in IEEE 1584

Industry standards and Industry standards and regulations:regulations:

OSHA 29 CFR 1910 OSHA 29 CFR 1910 Subpart SSubpart S

NFPA 70 - The NFPA 70 - The National Electrical National Electrical Code (2008 Edition)Code (2008 Edition)

NFPA 70E - Standard NFPA 70E - Standard for Electrical Safety for Electrical Safety in the Workplace in the Workplace (2004 Edition)(2004 Edition)

Arc Flash Hazard Analysis Key Arc Flash Hazard Analysis Key StepsSteps

Use NFPA 70EUse NFPA 70E** Tables, IEEE 1584, or Tables, IEEE 1584, or Lee Equations to Determine Lee Equations to Determine – Incident energy levels Incident energy levels – Arc Flash hazard distanceArc Flash hazard distance

* Use with extreme caution!* Use with extreme caution!

Arc Flash Hazard Analysis Key Arc Flash Hazard Analysis Key StepsSteps

Use Use – Calculated Incident Calculated Incident

EnergyEnergy– NFPA 70E Table NFPA 70E Table

130.7(C)(11) 130.7(C)(11) – to determine to determine

Hazard/Risk Hazard/Risk CategoryCategory

Required PPERequired PPE

Acceptable & Informative Acceptable & Informative LabelsLabels

NFPA 70E Table 130.7(C)NFPA 70E Table 130.7(C)(11)(11)

Short CircuitFault Study

Coordination (PDC)Study

Arc Flash StudyDevice Operating

Time

Arcing Fault Current

3 Phase Bolted

Fault Current

Arc Flash LabelEnergy Level

Boundaries

Required PPE

Obtain EquipmentNameplate Data

& Settings

Arc Flash Energy CalculationArc Flash Energy Calculation

Use Use 85%85%IaIa Determine Upstream Protective Determine Upstream Protective

Device Clearing Times (PDC Study)Device Clearing Times (PDC Study) Repeat process for Repeat process for 100%100%IaIa Use largest energy calculationUse largest energy calculation

Arc Flash Hazard Analysis Arc Flash Hazard Analysis Key StepsKey Steps

Determine:Determine:– Bolted Fault CurrentsBolted Fault Currents (Short Circuit (Short Circuit

Study)Study)– Arcing FaultArcing Fault (AF) Current (AF) Current– Upstream Protective Upstream Protective Device Device

Clearing TimesClearing Times (PDC Study) using (PDC Study) using AFAF

Arc Flash Hazard Analysis Arc Flash Hazard Analysis Key StepsKey Steps

Calculate Arc Flash EnergyCalculate Arc Flash Energy Use NFPA 70E Tables to Use NFPA 70E Tables to

determine:determine:– Glove Rating Class Glove Rating Class – Limited Approach BoundaryLimited Approach Boundary– Prohibited Approach BoundaryProhibited Approach Boundary– Restricted Approach Boundary Restricted Approach Boundary – Required PPERequired PPE

Arc Flash Hazard Analysis Key Arc Flash Hazard Analysis Key StepsSteps

Arc Flash Warning Labels Arc Flash Warning Labels showing showing the detailsthe details. .

How a Short Circuit Study is How a Short Circuit Study is PerformedPerformed

Obtain distribution system Obtain distribution system nameplate data for:nameplate data for:– TransformersTransformers– MotorsMotors– Circuit breakers, fuses, relaysCircuit breakers, fuses, relays– SwitchgearSwitchgear– Motor Control CentersMotor Control Centers– Conductor sizes and lengthsConductor sizes and lengths

How a Short Circuit Study is How a Short Circuit Study is PerformedPerformed

Enter dataEnter data into the into the computer program.computer program.

SimulateSimulate short short circuit at each circuit at each location and location and calculatecalculate the fault the fault current.current.

CompareCompare calculated calculated fault current to fault current to equipment short equipment short circuit rating. circuit rating.

What is Protective Device What is Protective Device Coordination (PDC) Study?Coordination (PDC) Study?

Determines:Determines:– fuse fuse sizessizes – SettingsSettings for for

relays and circuit relays and circuit breakersbreakers

– Device Device operating operating timetime

The study has The study has 22 conflicting goalsconflicting goals

Goal #1 - Maximum Selective Goal #1 - Maximum Selective Coordination Between Coordination Between

EquipmentEquipment CorrectCorrect fuse sizes and settings will fuse sizes and settings will

allow the device allow the device closest to a fault to closest to a fault to triptrip. .

If the If the first device failsfirst device fails to operate, then to operate, then the the next upstream devicenext upstream device will will triptrip..

LongerLonger device trip device trip delaysdelays = = increased increased devicedevice coordination coordination= = greatergreater incident incident energyenergy

Selective Selective CoordinationCoordination 3-MSWBD MAIN

SWBD

XFMR-UTILSS

P 2- XFMR-UTILS

5-Fdr to ATS-E

6-PNL-A MAIN

PNL-A - 250 A

E N

ATS 260 Amp

11

22

33

Goal #2 - Maximum Equipment Goal #2 - Maximum Equipment Protection and Reduction in Arc Protection and Reduction in Arc

Flash EnergyFlash Energy CorrectCorrect fuse sizes and device fuse sizes and device

settings will settings will quicklyquickly interruptinterrupt the the fault current for a short circuit fault current for a short circuit downstream.downstream.

ShorterShorter device delays = device delays = decreaseddecreased equipment damage = equipment damage = lessless Incident Incident Energy Energy

Maximum Maximum Equipment Equipment ProtectionProtection

(No Selective (No Selective Coordination)Coordination)

3-MSWBD MAIN

SWBD

XFMR-UTILSS

P 2- XFMR-UTILS

5-Fdr to ATS-E

6-PNL-A MAIN

PNL-A - 250 A

E N

ATS 260 Amp

11

11

11

Must Must balancebalance these these twotwo conflicting conflicting goals based upon the type of facility.goals based upon the type of facility.

PDC VocabularyPDC Vocabulary Time Current Curve (TCC)Time Current Curve (TCC) Log-log graph of Log-log graph of timetime versus versus

currentcurrent Every breaker, fuse, and relay has Every breaker, fuse, and relay has

a time current characteristic curve.a time current characteristic curve.

PDC Vocabulary PDC Vocabulary

Selective Device CoordinationSelective Device Coordination– The devices The devices plottedplotted on the on the time current time current

curvescurves are are coordinatedcoordinated for for allall levels of levels of fault current and time.fault current and time.

Fuse Fuse TCCTCC

3-6 Sec

5 kA

@15 kA

This Fuse is Current Limiting – Clearing time is 0.004 seconds

Thermal Thermal MagnetiMagnetic Trip c Trip UnitUnit

Thermal Thermal Unit is Unit is FixedFixed

Instant-Instant-aneousaneous– FixedFixed– AdjustablAdjustabl

ee

Thermal Thermal MagnetiMagneti

c c BreakerBreaker

20 kA0.01-0.025 Sec

4 kA

20-50 Sec

Solid Solid State State

Trip UnitTrip Unit SQ D NW SQ D NW

40H40H 4000 Amp4000 Amp MicrologicMicrologic

Current SensorsRating Plugs

Current Setting

Solid Solid State State

Trip UnitTrip Unit Varies for Varies for

each Trip each Trip Unit!Unit!

Some Some Functions Functions are Not are Not AdjustableAdjustable!!

Long Time Pickup (LTPU)

Long Time Delay (LTD)

Short Time Pickup (STPU)

Short Time Delay (STD)

Instantaneous (I)

Short Time Delay I2T-IN

(I2T)

Solid Solid State State TripTrip

SQ D NW SQ D NW 40H40H

4000 Amp4000 Amp MicrologicMicrologic

100 kA

0.01-0.06 Sec

6 kA

0.08-0.12 Sec 30 kA

170-210 Sec

Time Current CurvesTime Current Curves

An example of a TCC with Coordinated Devices

Current in Amperes X 100

Arc Flash Energy Arc Flash Energy CalculationsCalculations

Incident Energy Levels are Incident Energy Levels are dependent on: dependent on: – LevelLevel of of arcingarcing fault fault currentcurrent – Upstream device Upstream device clearing timeclearing time..

Multiple Sources Multiple Sources

Typical Assumptions for an Typical Assumptions for an AnalysisAnalysis

Trip timeTrip time is determined by the is determined by the upstream protectiveupstream protective device device settingssettings..

Worker is Worker is stationarystationary.. The The maximum timemaximum time that a worker that a worker

will be exposed to the arc flash is will be exposed to the arc flash is 2.0 seconds2.0 seconds. (Depends upon . (Depends upon location!!!)location!!!)

Current Vs Energy LevelsCurrent Vs Energy LevelsFault Current vs. Incident Energy

(Time Constant @ 0.025 Sec)

0 0 0

1 1 1 1 1 1 1

0

1

2

3

4

0 20 40 60 80 100

Fault Current

Inci

dent

Ene

rgy

Energy PPE Class

Time Vs Energy LevelsTime Vs Energy LevelsTime vs. Incident Energy

(Fault Current Constant @ 30 kA)

1 1 1 2 2 3 3 3 40

10

20

30

0 0.1 0.2 0.3 0.4 0.5 0.6

Device Operating Time

Incid

ent E

nerg

y

Incident Energy PPE Class

Distance Vs Energy LevelsDistance Vs Energy LevelsDistance vs. Incident Energy

(Time Constant @ 0.5 Sec & Fault = 60 kA)

0

124+ 34

01020304050

0 50 100 150 200 250

Distance (Inches)

Inci

dent

Ene

rgy

Energy Class

Arc Flash Warning LabelsArc Flash Warning Labels

What does it mean?What does it mean?

Limited Approach Limited Approach Boundary:Boundary:

An approach limit at a distance from An approach limit at a distance from an exposed live part within which a an exposed live part within which a shock hazard exists. This value is shock hazard exists. This value is determined by NFPA 70E (2004) Table determined by NFPA 70E (2004) Table 130.2(B).130.2(B).

Qualified PersonsQualified Persons Unqualified if accompanied by a Unqualified if accompanied by a

Qualified PersonsQualified Persons PPE not required if AF Boundary is not PPE not required if AF Boundary is not

in Limited Approach Boundaryin Limited Approach Boundary

Restricted Approach Restricted Approach BoundaryBoundary

An approach limit at a distance from An approach limit at a distance from an exposed live part within which an exposed live part within which there is an increased risk of shock, there is an increased risk of shock, due to electrical arc over combined due to electrical arc over combined with inadvertent movement, for with inadvertent movement, for personnel working in close proximity personnel working in close proximity to the live part. to the live part.

Determined by NFPA 70E (2004) Determined by NFPA 70E (2004) Table 130.2(B) Table 130.2(B)

Restricted Approach Restricted Approach BoundaryBoundary

Qualified Persons OnlyQualified Persons Only Must wear PPEMust wear PPE

Prohibited Approach Prohibited Approach BoundaryBoundary

An approach limit at a distance from An approach limit at a distance from an exposed live part within which an exposed live part within which work is considered the same as work is considered the same as making contact with the live part. making contact with the live part.

Determined by NFPA 70E (2004) Determined by NFPA 70E (2004) Table 130.2(B).Table 130.2(B).

Qualified Persons OnlyQualified Persons Only PPE Required as if in direct contactPPE Required as if in direct contact

Flash Protection RangeQualified Persons OnlyPPE Required if Flash Protection Boundary is CrossedFPB dependent on:

Voltage LevelFault levelTrip Time of Protective Device

Equipm

ent

Prohibited RangeLimited Approach Range Restricted Range

Limited Approach Range: Qualified or unqualified persons**Only if accompanied by Qualified Person

Restricted Boundary: Qualified Persons Only, PPE required

Prohibited Boundary: Qualified Persons Only. PPE required as if direct contact with energized part

Limited ApproachBoundary

(Fixed by Voltage)

Restricted Boundary(Fixed by Voltage)

Prohibited Boundary(Fixed by Voltage)

FlashProtectionBoundary

BoundaryVaries

Arc Flash Label InstallationArc Flash Label Installation Always clean the surface with detergent Always clean the surface with detergent

to remove all grease and dirt. Wipe to remove all grease and dirt. Wipe surface dry before applying the label.surface dry before applying the label.

Some locations will have a Line Side Some locations will have a Line Side Label. They should be installed at Label. They should be installed at locations where maintenance staff locations where maintenance staff could be exposed to energized parts on could be exposed to energized parts on the line side of a fuse or circuit breaker. the line side of a fuse or circuit breaker. Examples of this are Main Breakers in Examples of this are Main Breakers in Switchboards and Switchgear.Switchboards and Switchgear.

Arc Flash Label InstallationArc Flash Label Installation Transformer Labels are for small Transformer Labels are for small

distribution transformers (480/208 distribution transformers (480/208 V) where both the 480 and 208 Volts V) where both the 480 and 208 Volts terminals are exposed.terminals are exposed.

Locations where the label will be Locations where the label will be exposed to direct sun light should be exposed to direct sun light should be brought to the attention of brought to the attention of PowerStudies.com. We will provide PowerStudies.com. We will provide labels with a special UV protective labels with a special UV protective covering to protect the label from covering to protect the label from fading.fading.

Line Side vs Bus AF LabelsLine Side vs Bus AF Labels

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– ArticlesArticles– LinksLinks– Specifications for Power System StudiesSpecifications for Power System Studies

Short CircuitShort Circuit Protective Device CoordinationProtective Device Coordination Arc Flash HazardArc Flash Hazard

Phone: 253-639-8535Phone: 253-639-8535 Email: fuhr@powerstudies.comEmail: fuhr@powerstudies.com

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Questions?????Questions?????