Arc Flash Overview and Qualifications August 18 2009

7/29/2019 Arc Flash Overview and Qualifications August 18 2009

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Electrical Awareness

Arc Flash Overview & Qualifications

By:Joseph F. Maida, PEAugust 18, 2009

Fort Washington, PA

P 215.542.8700 F 215.542.5652

Orlando, FL

P 407.352.3300 F 407.352.3301

Visit us online at

www.MaidaEngineering.com


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Joseph F. Maida, P.E. President

Maida Engineering, Inc.Qualifications:

BSEE Drexel University 1971 MSEE Drexel University (Power) 1976

Licensed Electrical Contractor 1971 -1976

Officer - US Army Reserve 1971 1979

Delmarva Power & Light Co.1972 1974

Day & Zimmermann, Inc. 1974 -1978

Maida Engineering, Inc. 1978 Present

PE License PA -1975 (NJ, NY & DE 1976)

PE License ID, MA, RI, NC, GA, FL, TX, IA, WV, AKand Alberta, Canada

LEED Accredited Professional

PA UCC Review and Advisory Council


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Why the NEC?

The National Electrical Code NFPA 70- NEC is the least amended model

code in the world and no court in theUSA has faulted anyone for using the

latest version of the NEC, even when

the local code was not updated.1

2009 International Building Code has

incorporated the 2008 NEC.

1. http://en.wikipedia.org/wiki/National_Electrical_Code_(US)


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NECArticle

110.16 Flash Protection.

Equipment such as switchboards, panelboards,

industrial control panels, meter socket enclosures, and

motor control centers that are in other than dwelling

occupancies and are likely to require examination,adjustment, servicing, or maintenance while energized

shall be field marked to warn qualified persons of

potential electric arc flash hazards. The marking shall be

located so as to be clearly visible to qualified persons

before examination, adjustment, servicing, or

maintenance of the equipment.


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NECArticle

110.16 Flash Protection.

FPN No. 1: NFPA 70E-2004, Standard for Electrical Safety

in the Workplace, provides assistance in determining

severity of potential exposure, planning safe work practices,and selecting personal protective equipment.

FPN No. 2:ANSI Z535.4-1998, Product Safety Signs and

Labels, provides guidelines for the design of safety signsand labels for application to products.


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NECDefinition

Panelboard.

A single panel or group of panel units designed for

assembly in the form of a single panel, including buses

and automatic overcurrent devices, and equipped withor without switches for the control of light, heat, or

power circuits; designed to be placed in a cabinet or

cutout box placed in or against a wall, partition, or

other support; and accessible only from the front.


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NECDefinition

Switchboard.

A large single panel, frame, or assembly of panels on

which are mounted on the face, back, or both,

switches, overcurrent and other protective devices,buses, and usually instruments. Switchboards are

generally accessible from the rear as well as from the

front and are not intended to be installed in cabinets.


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NECDefinition

Motor Control Center.

An assembly of one or more enclosed sections having

a common power bus and principally containing motor

control units.

ARTICLE 312

Cabinets, Cutout Boxes, and Meter Socket

Enclosures

312.1 Scope. This article covers the installation and

construction specifications of cabinets, cutout boxes,

and meter socket enclosures.


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NECArticle 409.2

Industrial Control Panel.An assembly of two or more

components consisting of one of the following:(1) Power circuit components only, such as motor controllers,

overload relays, fused disconnect switches, and

circuit breakers

(2) Control circuit components only, such as pushbuttons,pilot lights, selector switches, timers, switches, control

relays

(3) A combination of power and control circuit components

These components, with associated wiring and terminals,

are mounted on or contained within an enclosure or

mounted on a sub-panel. The industrial control panel does

not include the controlled equipment.


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NECDefinition

NFPA 70 National Electrical Code, 2008 Edition

Qualified Person. One who has skills and

knowledge related to the construction and

operation of the electrical equipment andinstallations and has received safety training

to recognize and avoid the hazards involved.

FPN: Refer to NFPA 70E-2004, Standard fo r Electr ical

Safety in the Workplace, for electrical safety training

requirements.


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Qualified Person

NFPA 70 E Standard for Electrical Safety in the Workplace,

2009 Edition

Qualified Person.A qualified person shall be:

Trained and knowledgeable of the constructionand operation of equipment or a specific work

method

Trained to recognize and avoid the electrical

hazards that might be present with respect tothat equipment or work method.


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Qualified Person


2009 Edition

Qualified persons shall be familiar with the

proper use of:

The special precautionary techniques,

Personal Protective Equipment, including

Arc-flash,

Insulating and Shielding materials,

Insulated tools and test equipment.


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Qualified Person


2009 Edition

A person can be considered qualified withrespect to certain equipment and

methods but still be unqualified for

others.


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What is an Arc Flash?

Question

What is an arc flash?


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Arc Flash


2009 Edition Appendix K

Arc-Flash - When an electric current passes through air

between ungrounded conductors or between

ungrounded conductors and grounded conductors.

Exposure to these extreme temperatures both burns

the skin directly and causes ignition of clothing, which

adds to the burn injury.

Arc-flashes can and do kill at distances of 3 m (10 ft).


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Arc-Flashes occurs when electricity flows through airbetween two (2) parts of a power circuit which are not atthe same voltage. The parts could be two (2) conductorsof different phases or a phase conductor and groundwhen the system is grounded.

Arc flashes are more likely to occur where dust or

humidity are present or after an initial electrical short

because the vaporized particles provide low impedance

media for current to flow between the phases or to

ground.

Circuit breakers can explode if subjected to short circuit

currents higher than their rating.


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Electricity can flow through any medium but cannot flowthrough a vacuum. Insulated materials present a

significantly high impedance but will conduct more

electricity as the voltage increases.

The majority of hospital admissions due to electrical

accidents are from arc-flash burns.

Each year more than 2,000 people are admitted to burn

centers with severe arc-flash burns. Almost 5 peopleevery day.

Hazards are shown on the following slide.


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Flame Retardant Clothing

Provides added protection from arc flash

burns only!

-----------------------------------------------------------

Electrical hazards are shown on thefollowing slide.


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Electric Hazards

Electric Shock Electricity, resulting fromelectromagnetism, passing through the body can

cause shock, cardiac arrest and internal burns.

Arc-Flash Burns Caused by air that can reach

35,000 F. Hotter than the sun! Hot enough to vaporize

metal.

Arc-Flash Blasts Pressure waves that will throw a

person away from the blast into walls and otherequipment or off ladders and platforms.


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Electric Hazards

Intense Light Electric arcs can create light that willdamage eyes and may cause cataracts years later.

Sound Waves Noise levels that can cause temporary

or permanent loss of hearing

Projectiles Molten pieces of metal, vapors and

shrapnel that can penetrate flame retardant clothing.


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Why now and not before?

Question



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Electrical power distribution system are being designedto generate and distribute more electrical energy.

Personnel are more often exposed to recognized

electrical hazards that could cause death or seriousphysical harm when examining, adjusting, servicing,

or maintaining electrical equipment.

Understanding of the arc flash hazards has increased

Personal Protective Equipment (PPE) to prevent death

or severe injuries due to arc flash burns are available.


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In the early 1980s, Dupont developed flame retardant

material (Nomex).

Ralph Lee, a Dupont Consultant, looking for uses

for the new flame retardant material, performed tests

to determine the effect heat from an electric arc flashwould have on human skin.

Ralph Lee developed the first set empirical equations \

that could be used to calculate incident energyassociated with an arc flash. The equations are still used

for electrical power systems rated above 15,000 Volts.


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Ralph Lees work showed that skin temperatures above

96C for .1 seconds or 6 cycles would result in incurable

3rd degree burns and that at a temperature of 80C the

skin would be just curable or sustain a 2nd degree

burn.

In 1998, Dougherty, Neill and Floyd developed the first

Equations which considered the effect of an arc in a box

versus an arc in open air. They developed the Arc

Hazard Classifications for flame retardant clothing. Theirequations are only for systems rated below 1,000 volts

with short circuit currents between 16,000 and 50,000

amps. Equations are no longer utilized.


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Why now and not before? An IEEE industry group sponsored by petroleum and

chemical industries developed the latest formulas thatare published in the IEEE Standard 1584 - 2002 Guide

for Performing Arc Flash Calculations. It contains:

Empirical formulas, derived from tests that can be

used for 3 power systems up to 15,000 volts and forshort circuit currents between 700 and 106,000 amps.

Generally, no need for calculation on systems rated at

50 volts or less and on systems rated 240 volt andless that are derived from transformers rated less than

125 KVA. The guide does not state if this rating is for

1 and 3 transformers.


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Why now and not before? IEEE Standard 1584 - 2002 Guide for Performing Arc

Flash Calculations contains equations to calculateArc Flash Incident Energy based on:

The short circuit current and duration of an arc that

consider if the arc occurs within a box or in open air

and if the power system is grounded or ungrounded.

The short circuit current and the type of fuse or circuit

breaker, if the arc flash current will trip the circuit

breaker or blow the fuse.

Incident Energy is the amount of energy impressed on a

surface a certain distance from the source.


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Occupational Safety and Health Administration (OSHA)

was created in 1971.

OSHA has worked with employers and employees to

provide a better working environment and since its

creation, has helped to cut workplace fatalities by morethan 60 percent and occupational injury and illness rates

by 40 percent while employment in the United States has

doubled.1

OSHA is part of the US Department of Labor.

OSHA regulations are written under Title 29 of the Code

of Federal Regulations

1. http://www.osha.gov/as/opa/oshafacts.html


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On January 16, 1981, OSHA by reference incorporated

the relevant requirements from Part 1 of then new NFPA

70E -1979 as its electrical standard for general industry.

The first substantial changes to NFPA 70E wereintroduced in 1995 and included a consensus standard

on work practices and PPE application based on

theoretical modeling developed by Ralph Lee.

Subpart S of 29 CFR Part 1910 was updated on August

13, 2007 to reference NFPA 70E 2000 and NFPA 70

2002.


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Calculations:

-Methods and Empirical Equations Developed by

- Ralph Lee - 1981

- IEEE Group (1584) 2002

Charts:-Published within NFPA 70E 2004

Calculators

-Provided with IEEE 1584 2002

Computer Software

-Developed by SKM Systems Inc. and others


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Calculation - IEEE Group (1584) 2002

Empirical Formulas that consider for many variables

including short circuit current and time of exposure.

Formulas specific to types of fuses.

General Formulas that are based on fuse or breaker

sizes and available short circuit current.

Defines when calculations are not required.

Refers to Lees equations for systems greater than

15,000 Volts.


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Why adhere to NFPA 70 E

Question

Why adhere to NFPA 70E Article 130 -

Working on or near live parts ?


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OSHA

Non-mandatory Compliance Guidelines for Hazard

Assessment and Personal Protective EquipmentSelection.

- 1910 Subpart I App B

Electrical Codes

NFPA 70 National Electrical Code, 2008 Edition

NFPA 70E Standard for Electrical Safety in the Workplace,

2009 Edition


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Why adhere to NFPA 70 E?

With the addition of Article 110.16 in the 2002

National Electrical Code (NEC), employers

and employees have become aware of electric

arc flash hazard.

With the publication of NFPA 70E Standard for

Electrical Safety in the Workplace, 2009 Edition,

employers and employees have methods to

safeguard employees from at least one of theelectric arc flash hazards.

1: NFPA 70E Standard for Electrical Safety in the Workplace, 2004 Edition


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Why adhere to NFPA 70 E?


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January 9, 2002

Conclusion:

Though OSHA does not, per se, enforce NFPA 70EStandard, 2000 Edition, OSHA considers the NFPAStandard a recognized industry practice.

The employer is required to conduct hazardassessment in accordance with 29 CR 1910.132(d)(1).

If a arc flash hazard is present, or likely to be

present, then the employer must select and requirethe employees to use the selected apparel.


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January 9, 2002

Employers who conduct the hazard/riskassessment, and select and require theiremployees to use protective clothing andother PPE appropriate for the task, as statedin NFPA 70E 2000 edition, are deemed incompliance with the Hazard Assessment andEquipment Selection OSHA Standard

U. S. Department of Labor Jan. 9, 2002


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OSHA

OSHA commonly uses the General Duty Clause,

which is paraphrased below or as an alternateusesNFPA 70E or the NEC for citations related to arc

flash incidents.

General Duty Clause:

Section 5(a)(1) of the Occupational Safety and

Health Act requires an employer to furnish to its

employees employment and a place of

employment which are free from recognized

hazards that are causing or are likely to cause

death or serious physical harm to his

employees.


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Answer

It is the right thing to do!


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Arc Flash Labels

Question

What is and where are Arc Flash Label

Required?


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Arc Flash Labels

Arc Flash labels are requiredon equipment such aspanelboards, switchboards, motor control centers,industrial control panels and meter sockets,

Arc Flash labels are required on motor starters,

variable frequency drives, plug-in bus duct, equipmentcontrol panels and building management panels if theycontain equipment that is 50 volts or higher and arelikely to require examination, adjustment, servicing ormaintenance while energized.


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Arc Flash Hazard Labels

The following arc flash label would suffice in meeting the

requirements of NEC Article 110.16 but may not suffice

in meeting NFPA 70E 2009.

Equipment Labeling. Equipment shall be field marked

with a label containing the available incident energy

or required level of PPE.

1. NFPA 70E 2009


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Arc flash labels can contain other information that can

be provided by the owner or employer to the employee

when needed based on the system configuration at the

time


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Arc Flash Hazard Labels Limited Approach: The closest distance an unqualified

person can approach unless made aware of the dangerand accompanied by a qualified person.

Restricted Approach: The closet distance a qualified

person can approach with proper PPE and tools.

Prohibited Approach: The minimum distance to prevent

flashover and arcing.

Flash Protection Boundary: The distance where theenergy from the arc will not cause a 3rd degree burn to

unprotected skin.


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Sh k H d A l i


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Shock Hazard Analysis

Electric Shock Hazard Analysis

The following chart is the basis fordetermining electric shock boundaries. It iscontained within NFPA 70 E 2009.

The actual chart covers voltage as high as800,000 volts.

Sh k H d A l i


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Shock Hazard AnalysisTable 130.2(C) Approach Boundaries to Energized Electrical Conductors or Circuit

Parts for Shock Protection (All dimensions are distance from energized electrical

conductor or circuit part to employee

LimitedApproach Boundary RestrictedApproach

Nominal System Exposed Exposed Boundary; Includes Prohibited

Voltage Range, Movable Fixed Inadvertent Movement Approach

Phase to Phase Conductor Circuit Part Adder Boundary

Less than 50 Not specified Not specified Not specified Not specified

50 to 300 10 ft 0 in. 3 ft 6 in Avoid contact Avoid contact

301 to 750 10 ft 0 in. 3 ft 6 in. 1 ft 0 in. 1 in.

751 to 15 kV 10 ft 0 in. 5 ft 0 in. 2 ft 2 in. 7 in.

15.1 kV to 36 kV 10 ft 0 in. 6 ft 0 in. 2 ft 7 in. 10 in.

A Fl h H d A l i


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Arc Flash Hazard Analysis

Arc Flash Hazard Analysis are performedto determine the

Arc Flash Hazard Category

And

Arc Flash Protection Boundary

A Fl h L b l


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Arc Flash Labels Arc Flash Hazard Analysis.An arc flash hazard

analysis shall determine the Arc Flash ProtectionBoundary and the Personal Protective

Equipment that people, within the Arc Flash

Protection Boundary, shall use.1

The Arc Flash Protection Boundary is the

distance at which a person is likely to receive a

second-degree burn.

All parts of the body inside the Arc Flash

Protection Boundary shall be protected.1

1. NFPA 70E -2009

A Fl h H d A l i


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Arc Flash Hazard Category Is used to definethe appropriate level of Personnel Protective

Equipment based on a working distance in front

of exposed electrical parts and circuits.

Exposed - Capable of being inadvertently

touched or approached nearer than a safe

distance by a person. It is applied to electrical

conductors or circuit parts that are not suitablyguarded, isolated, or insulated.1.

1. NFPA 70E -2009

A Fl h H d A l i


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Typical working distances used for incident energy

calculations are as follows:

Low voltage (600 V and below) MCC and panelboards

455 mm (18 in.)

Low voltage (600 V and below) switchgear

610 mm (24 in.)

Medium voltage (above 600 V) switchgear

910 mm (36 in.)

Reference NFPA 70E 2009 Appendix D

A Fl h H d A l i


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Almost all arc flash analysis require knowing theavailable short circuit current.

Table 130.7(C)(9)within NFPA 70E -2009 can be used

in lieu of arc flash calculations if one know the maximum

available 3 phase bolted fault current and theovercurrent device clearing time at and for the

equipment.

Part of the Table 130.7(C)(9) Hazard/Risk Category

Classifications and Use of Rubber Insulating Gloves andInsulated and Insulating Hand Tools from NFPA 70E

2009 and selected footnotes for the Table are shown on

the following slides.

A Fl h H d A l i


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Arc Flash Hazard AnalysisTable 130.7 (C)(9) from NFPA 70E - 2009

Task Performed on Energized Equipment Hazard/Risk V-rated V-ratedCategory Gloves Tools

Panelboards and Other Equipment Rated 240 V and Below

Notes 1

Perform infrared thermography and other non-contact

inspections outside the restricted approach boundary 0 N NCircuit breaker (CB) or fused switch operation with covers on 0 N N

CB or fused switch operation with covers off 0 N N

Work on energized electrical conductors and circuit parts,

including voltage testing 1 Y Y

Remove/install CBs or fused switches 1 Y Y

Removal of bolted covers (to expose bare, energized electrical

conductors and circuit parts) 1 N NOpening hinged covers (to expose bare, energized electrical

conductors and circuit parts) 0 N N

Work on energized electrical conductors and circuit parts of

utilization equipment fed directly by a branch circuit of the

Panelboard 1 Y Y

A Fl h H d A l i


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Footnotes from Table 130.7 (C)(9) NFPA 70E -2009

1. 25 kA short circuit current available, 0.03 second (2

cycle) fault clearing time.

2. 65 kA short circuit current available, 0.03 second (2

cycle) fault clearing time.

Generally, the short circuit current must be within the

instantaneous operating time of the circuit breaker or thecurrent limiting range of a current limiting fuse.

A Fl h H d A l i


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Table 130.7 (C)(9) from NFPA 70E - 2009

Both larger and smaller available short-circuit currents

could result in higher available arc flash energies.

* If the available short-circuit current increases withouta decrease in the opening time of the overcurrent

protective device, the arc flash energy will increase.

* If the available short-circuit current decreases,resulting in a longer opening time for the overcurrent

protective device, arc flash energies could also

increase.1.

1. NFPA 70 E 2009


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S

ourceo

fPowe

r

A Fl h H d A l i


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Arc Flash Ha ard Anal sis


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Who is Qualified?

Q lifi d P


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Qualified Person


2009 Edition

Qualified persons permitted to work within the

Limited Approach Boundary of exposed energized

electrical conductors and circuit parts operating at 50volts or more shall, at a minimum, be additionally

trained in all of the following:

(1) The skills and techniques necessary to

distinguish exposed energized electrical conductors

and circuit parts from other parts of electrical

equipment.

Q lifi d P


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Qualified Person


2009 Edition(2) The skills and techniques necessary to determine

the nominal voltage of exposed energized electrical

conductors and circuit parts

(3) The approach distances specified in Table 130.2(C)

and the corresponding voltages to which the

qualified person will be exposed.

(4) The decision-making process necessary todetermine the degree and extent of the hazard and

the personal protective equipment and job planning

necessary to perform the task safely

Task Qualified Person


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Task Qualified Person


2009 Edition

An employee who is undergoing on-the-job training

and who, in the course of such training, has

demonstrated an ability to perform duties safely athis or her level of training and who is under the direct

supervision of a qualified person shall be considered

to be a qualified person for the performance of those

duties.

Tasks that are performed less often than once per

year shall require retraining before the performance

of the work practices involved.

Qualified Person


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Qualified Person


2009 Edition

Employees shall be trained to select an appropriate

voltage detector and shall demonstrate how to use a

device to verify the absence of voltage, includinginterpreting indications provided by the device. The

training shall include information that enables the

employee to understand all limitations of each

specific voltage detector that may be used.

Qualified Person


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Qualified Person


2009 Edition

The employer shall document that each employee

has received the training required. This

documentation shall be made when the employeedemonstrates proficiency in the work practices

involved and shall be maintained for the duration of

the employees employment. The documentation

shall contain each employees name and dates of

training.

NFPA 70E 2009


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NFPA 70E - 2009

The arc flash hazard analysis shall take into

consideration the design of the overcurrent

protective device and its opening time, including its

condition of maintenance.

Exception No. 1: An arc f lash hazard analysis shal l

no t be required where al l of the fol low ing condi t ions

exist:

(1) The circu it is rated 240 volts or less .

(2) The circu i t is supp l ied by one trans form er.

(3) The transfo rmer supplyin g the circui t is rated less

than 125 kVA.



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Therefore, there is NO requirement todetermine the following for AC power system

rated below 240 Volts and above 50 volts

originating from one transformer rated below

125 KVA.

Arc Flash Protection Boundary

Personal Protective Equipment

Arc Flash Hazard Category



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The following arc flash label would suffice in meeting the

requirements of NEC Article 110.16 and NFPA 70E2009.



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NFPA 70 E defines Arc Flash Protection Boundary

as follows

When an arc flash hazard exists, an approach

limit at a distance from a prospective arc source

within which a person could receive a seconddegree burn if an electrical arc flash were to

occur



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NFPA 70E states the following:

When an employee is working within the Arc Flash

Protection Boundary he or she shall wear

protective clothing and other personal protectiveequipment in accordance with 130.3. All parts of

the body inside the Arc Flash Protection Boundary

shall be protected.



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IEEE 1584 2002 states the following relative to

the use of PPE:

Where used, PPE for the arc-flash hazard is the

last line of defense. The protection is not intended

to prevent all injuries but to mitigate the impact ofan arc flash upon the individual, should one occur.

In many cases, the use of PPE has saved lives or

prevented injury. The calculations in this guide will

lead to selection of a level of PPE that is a balancebetween the calculated estimated incident energy

exposure and the work activity being performed

while meeting the following concerns:



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a)The desire to provide enough protection to

prevent a second degree burn in all cases.

b) The desire to avoid providing moreprotection than is needed. Hazards may be

introduced by the garments such as heat

stress, poor visibility, and limited body

movement.



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Without arc flash hazard analysis, which at aminimum requires the determination of the

potential short circuit current and knowledge

of the overcurrent protective device, short of

testing, it is impossible to determine theIncident Energy.

Therefore, without arc flash hazard analysis,

the only information that can be included onlabel is the Required Level of PPE.



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NFPA 70 E does not define what is meant bythe Required Level of PPE and it only

defines methods that should be used for the

selection of protective clothing and other

personnel protective equipment for workperformed within the Arc Flash Protection

Boundary.



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Arc Flash Labels used to mark equipment for

which arc flash hazard analysis has not beenperformed should indicate that the Level of

PPE shown on the label are

DEFAULTAnd

NO ARC FLASH HAZARD ANALYSIS WAS

PERFORMED

An Arc Flash Protection Boundary need not

be listed on the label.



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Considering that the hazard within theequipment could be equivalent to the hazard

associated with changing a 120 volt. 100 watt

light bulb, the requirement for PPE should

depend on the type of equipment.

Examples of Level of PEE that could be

defined on a label, as determined by the

employer, could include:



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Panelboards Arc Hazard Category 0

Industrial Control Panels - Arc Hazard Category 0

Motor Controllers Arc Flash Hazard Category 0

Building Management Panels No Arc Flash Hazard

Category

Instrumentation Panels - No Arc Flash HazardCategory



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Even if no Arc Flash HazardCategory is defined, Safety glasses

or goggles and hearing protection

should be required for anyelectrical work near exposed

energized parts except for circuits

originating from Class II powersources as defined by Section 725

of the NEC.



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Based on the selection of standard personalprotective equipment (PPE) levels (1.2, 8, 25,

and 40 cal/cm2), it is estimated that the PPE

is adequate or more than adequate to protect

employees from second-degree burns in 95

percent of the cases.



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IncidentEnergyFromCal/cm2

IncidentEnergyFromCal/cm2

FRClothingClass

No.

ClothingDescription

0.0 1.2 0 Non-melting, flammablematerials

1.2 4.0 1 Arc Rated Shirt & Pants4.0 8.0 2 Arc Rated Shirt & Pants

8.0 25.0 3Arc Rated Shirt & Pants

& Arc Suit

25.0 40.0 4Arc Rated Shirt & Pants

& Arc Suit



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When incident energy exceeds 40

cal/cm2 at the working distance, greater

emphasis than normal should be placed

on de-energizing before working on or

near the exposed electrical conductors orcircuit parts.



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What are the formulas?



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SKM Software Incident Energy Calculations:

To determine the incident energy based on the arcing

fault currents, first use empirically derived equation

shown on the next slide to determine the log10 of the

normalized incident energy.

The equation is based on data normalized for an arc time

of 0.2 second and a distance from the possible arc point

to the person of 610 mm.

Afterwards convert from the normalized value using the

equations on the subsequent slides.



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Arc Flash Hazard AnalysisFor Applications with system voltages below 1,000 Volts

where:

lg = the log10Ia = arcing current in kA

K = -0.153 foropen air arcs; -0.097 forarcs-in-a-box

Ibf = bolted three-phase available short-circuit current

(symmetrical rms) (kA) between 700 and 106,000 ampsV = system voltage in kV

G = conductor gap (mm) (See Table on following slide)



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Arc Flash Hazard AnalysisFor applications with a voltage of 1,000 Volts or higher:

where:

lg = the log10Ia = arcing current in kA

Ibf = bolted three-phase available short-circuit current

(symmetrical rms) (kA)

V = system voltage in kV

G = conductor gap (mm) (See Table on previous slide)



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Arc Flash Hazard AnalysisTable D.8.2 Factors for Equipment and Voltage Classes

System Typical

Voltage Conductor Distance(kV) Type of Equipment Gap (mm) X-Factor

-------------------------------------------------------------------------------------------

Open-air 1040 2.000

0.2081 Switchgear 32 1.473

MCCs and panels 25 1.641Cables 13 2.000

-----------------------------------------------------------------------------------------

Open-air 102 2.000

>15 Switchgear 13102 0.973

Cables 13 2.000Open-air 13153 2.000

--------------------------------------------------------------------------------------

>515 Switchgear 153 0.973

Cables 13 2.000



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Arc Flash Hazard AnalysisFor all applications two (2) time durations are used to

calculate the incident energy from the TCC Curve:

Use 0.85Ia to find a second arcing time. This second arc

current accounts for variations in the arcing current and

the time for the overcurrent device to open.

Calculate the incident energy using both values (Ia and

0.85 Ia), and use the higher value.


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Sourceo

fPowe

r



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Arc Flash Hazard AnalysisNormalized Incident Energy Calculations:

where:

En = incident energy (J/cm2) normalized for time anddistance

k1 = -0.792 for open air arcs; -0.555 for arcs-in-a-box

k2 = 0 for ungrounded and high-resistance grounded

systems= -0.113 for grounded systems

G = the conductor gap (mm) (See Table on previous

slide)



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Arc Flash Hazard AnalysisConverting from Normalized Incident Energy:

where:

E = incident energy in J/cm2

Cf = calculation factor

= 1.0 for voltages above 1 kV= 1.5 for voltages at or below 1 kV

En = incident energy normalized

t = arcing time (seconds) from TCC Curve

D = distance (mm) from the arc to the person (workingdistance)

X = the distance exponent from Table on

previous slide



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Arc Flash Hazard AnalysisFlash Boundary Calculation:

The Flash Protection Boundary is the distance at

which a person is likely to receive a second-degree

burn. The onset of a second-degree burn is assumed

to be when the skin receives 5.0 J/cm2 or 1.2 cal/cm2

of incident energy.

The formula on the following slides is then used to

calculate the Flash Boundary Distance.



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Arc Flash Hazard AnalysisFlash Boundary Calculation:

where:

DB = the distance (mm) of the Flash Protection Boundary from the

arcing point

Cf

= a calculation factor

= 1.0 for voltages above 1 kV

= 1.5 for voltages at or below 1 kV

En = incident energy normalized

EB = incident energy in J/cm2 at the distance of the Flash

Protection Boundary

t = time (seconds)X = the distance exponent from Table 10.8.2

Ibf = bolted three phase available short-circuit current

V = system voltage in kV



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Equations for estimating incident energy and Flash

Protection Boundaries based on statistical analysis andcurve fitting of available test data was produced by an

IEEE working group that produced the data from tests it

performed to produce models of incident energy.

Based on the selection of standard personal protective

equipment (PPE) levels (1.2, 8, 25, and 40 cal/cm2), it is

estimated that the PPE is adequate or more than

adequate to protect employees from second-degree

burns in 95 percent of the cases.



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c as a a d a ys s

Question

What can be done to reduce arc flash

exposure?



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yDesign with Arc Flash in mind

Install smaller transformers

112.5 KVA or less for 240 Volt and 120/208 Volt Power

Systems.

Compartmentalize

Use individual secondary main circuit breakers that are

in separate compartments or enclosures

Require designs that have a maximum arc flash hazard

incident energy of 8 cals/cm2.



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yDesign with Arc Flash in mind

Do not oversize transformers

KVASC = KVABASE / ZPU

ISC = (KVASC X 1000) / (VLL X 1.732)

where ISC is in amperes, VLL is in volts, and ZPU is

based on the transformer rated KVA

Install new light sensing relays in medium voltage

switchgearApply overcurrent protective devices properly

Use circuit breakers with a maintenance instantaneous

trip switch.



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y

NFPA 70 National Electrical Code, Many Editions

110.9 Interrupting Rating.

Equipment intended to interrupt current at fault levels shall

have an interrupting rating sufficient for the nominal circuitvoltage and the current that is available at the line terminals

of the equipment.

Equipment intended to interrupt current at other than fault

levels shall have an interrupting rating at nominal circuit

voltage sufficient for the current that must be interrupted.



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y

Arc Flash Hazards can be reduced by clearing the arcing

fault faster by doing one of the following: Reduce Existing Pickup and Delay Settings wherever

possible.

Enable Instantaneous Functions or Retro-fit with

Instantaneous Functions Reduce Fuse Sizes wherever possible.

Use Current-limiting breakers or fuses for high arcing

fault currents

Add Differential Protection

Use Temporary Instantaneous Trip Settings when workis being performed

Add optical sensors to trip when flash occurs

Flash Hazard Analysis


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y



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y

Must consider all of the sources of power including

generators run in parallel and motors.

Cannot account for services that only have overload

protection and hence must be consider DANGEROUS.

Must account for current limiting fuses operating within

the current limiting range.

Panelboards on the secondary of a transformer may

present a very high hazard because the trip time of thetransformers primary protection is very long for a fault on

the secondary of the transformer.



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y



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y

Arc Flash Hazards can be reduced by current limitingfuses.

The clearing time for a current limiting fuse is

approximately cycle or 0.004 second. The clearingtime of a 5 kV and 15 kV circuit breaker is

approximately 0.1 second or 6 cycles. This can be

broken down as follows: actual breaker time

(approximately 2.0 cycles), plus relay operating time of

approximately 1.74 cycles, plus an additional safetymargin of 2 cycles, giving a total time of approximately

6 cycles.



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y

Arc Flash Hazards can be reduced by: Current Limiting

Fuses and Cable Limiters



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y

Arc Flash Hazards can be reduced by: Current Limiting

Fuses and Cable Limiters

Arc Flash Analysis


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Question

What is required to do an arc flash

analysis?

Arc Flash Analysis


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All analyses require the following:

Accurate One Line Diagrams

Overcurrent Device Equipment Data

Realistic Short Circuit Current Calculations

Arc Flash Calculations or Fault Clearing Time.

A copy of NFPA 70E Standard for Electrical Safety inthe Workplace, 2004 Edition

Arc Flash Analysis


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General arc flash study procedure1

1. Collect field data sufficient to perform a short-circuit and

coordination study.

2. Identify the possible system operating modes including

tie-breaker positions, parallel generation, etc.

3. Calculate the bolted fault current at each fault location.

4. Calculate the arcing fault current flowing through eachbranch for each fault location.

1. Arc Flash Users Guide SKM Power Systems, Inc.

Arc Flash Analysis


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General arc flash study procedure1

5. Determine the time required to clear the arcing fault

current using the protective device settings and

associated trip curves.

6. Select the working distances based on system voltageand equipment class.

7. Calculate the incident energy at each fault location.

8. Calculate the flash protection boundary at each fault

location.

1. Arc Flash Users Guide SKM Power Systems, Inc.

Overall Benefits


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Question

What are the overall benefits of an arc

flash analysis?

Overall Benefits


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Why Perform Arc Flash Studies?

Possibly prevent worker injury or death

Avoid or reduce litigation expense associated with an

electrical injury.

Comply with codes and safety regulations (OSHA,

NFPA, NEC) thereby avoiding citations and fines.

Insurance requirements

Because you can and you want to!

Overall Benefits


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Potential Benefits from an Arc Flash Studies?

Lesson injuries caused by an arc flash thus increasing

worker safety and productivity.

Minimize equipment damage and system down time

Increase selectivity and hence the reliability of the

Power Distribution System.

Reduce the cost of future electrical projects.

Reduce maintenance cost.

Arc Flash Summary


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Proper Maintenance

Define and follow necessary PM procedures

Knowledge

Understand the true dangers of electricity

Planning

Develop and follow a work plan that includesidentifying the arc flash hazard

STAY ALERT STAY WELL STAY ALIVE

Questions?


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Additional Presentations

ARC FLASH OVERVIEW

ARC FLASH LABELS AND REPORTING REQUIREMENTS

FR CLOTHING AND PPE

PERFORMING ARC FLASH ANALYSIS VS USING CHARTS & TABLES

UNDERSTANDING SHORT CIRCUIT AND ARC FLASH CALCULATIONS

AN OVERVIEW IEEE 1584

Joseph MaidaPresident

www.MaidaEngineering.com

Documents

Arc Flash Overview and Qualifications August 18 2009