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Arc Flash _ Electrical Safety

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Arc Flash _ Electrical Safety Powered By Docstoc
					             Electrical Awareness
      Arc Flash Overview & Qualifications
                     By: Joseph F. Maida, PE
                                August 18, 2009




Fort Washington, PA
P 215.542.8700 F 215.542.5652

Orlando, FL                                              Visit us online at
P 407.352.3300 F 407.352.3301               www.MaidaEngineering.com
                                                                   1
         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, AK
  and Alberta, Canada
 LEED Accredited Professional
 PA UCC Review and Advisory Council
                                                        2
                         Why the NEC®?


 The National Electrical Code NFPA 70
      - NEC® is the least amended model
      code in the world and no court in the
      USA 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)   3
                     NEC® Article
               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.
                                                      4
                     NEC® Article

                 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 signs
and labels for application to products.



                                                             5
                 NEC® Definition

                    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 with
  or 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.


                                                    6
                NEC® Definition

                   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.




                                                    7
                 NEC® Definition
              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.
                                                     8
                  NEC® Article 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.
                                                             9
                 NEC® Definition
     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 and
installations and has received safety training
to recognize and avoid the hazards involved.

FPN: Refer to NFPA 70E®-2004, Standard for Electrical
Safety in the Workplace, for electrical safety training
requirements.
                                                          10
                 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 construction
   and operation of equipment or a specific work
   method
  Trained to recognize and avoid the electrical
   hazards that might be present with respect to
   that equipment or work method.

                                                         11
                 Qualified Person
NFPA 70 E Standard for Electrical Safety in the Workplace,
                       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.
                                                         12
                 Qualified Person
NFPA 70 E Standard for Electrical Safety in the Workplace,
                       2009 Edition



A person can be considered qualified with
     respect to certain equipment and
    methods but still be unqualified for
                  others.



                                                         13
What is an Arc Flash?




       Question

  What is an arc flash?

                          14
                       Arc Flash
NFPA 70 E Standard for Electrical Safety in the Workplace,
              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).


                                                           15
           What is an Arc Flash?
 Arc-Flashes occurs when electricity flows through air
  between two (2) parts of a power circuit which are not at
  the same voltage. The parts could be two (2) conductors
  of different phases or a phase conductor and ground
  when 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.
                                                               16
          What is an Arc Flash?
 Electricity can flow through any medium but cannot flow
  through 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 people
  every day.

 Hazards are shown on the following slide.
                                                            17
          What is an Arc Flash?
        Flame Retardant Clothing
Provides added protection from arc flash
             burns only!

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

   Electrical hazards are shown on the
              following slide.

                                                          18
What is an Arc Flash?




                        19
            Electric Hazards
     Electric Shock – Electricity, resulting from
  electromagnetism, 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 other
      equipment or off ladders and platforms.


                                                       20
             Electric Hazards
Intense Light – Electric arcs can create light that will
  damage 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.



                                                           21
Why now and not before?




         Question
  Why now and not before?
                            22
       Why now and not before?
 Electrical power distribution system are being designed
  to generate and distribute more electrical energy.

 Personnel are more often exposed to recognized
  electrical hazards that could cause death or serious
  physical 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.

                                                             23
      Why now and not before?
 In the early 1980’s, 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 flash
  would have on human skin.

 Ralph Lee developed the first set empirical equations \
  that could be used to calculate “incident energy”
  associated with an arc flash. The equations are still used
  for electrical power systems rated above 15,000 Volts.

                                                              24
      Why now and not before?
 Ralph Lee’s work showed that skin temperatures above
  96°C for .1 seconds or 6 cycles would result in incurable
  3rd degree burns and that at a temperature of 80°C 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. Their
  equations 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.
                                                           25
     Why now and not before?
 An IEEE industry group sponsored by petroleum and
  chemical industries developed the latest formulas that
  are 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 3Ø power systems up to 15,000 volts and for
    short 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 and
    less that are derived from transformers rated less than
    125 KVA. The guide does not state if this rating is for
    1Ø and 3Ø transformers.
                                                         26
     Why now and not before?
 IEEE Standard 1584 - 2002 Guide for Performing Arc
  Flash Calculations contains equations to calculate
  Arc 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.
                                                           27
       Why now and not before?
 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 more
  than 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
                                                         28
  1. http://www.osha.gov/as/opa/oshafacts.html
      Why now and not before?
 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 were
  introduced 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.
                                                           29
      Why now and not before?
 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
                                                      30
      Why now and not before?
 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 Lee’s equations for systems greater than
   15,000 Volts.
                                                           31
  Why adhere to NFPA 70 E




             Question

Why adhere to NFPA 70E Article 130 -
 “Working on or near live parts “?
                                       32
    Why adhere to NFPA 70 E
                        OSHA

   Non-mandatory Compliance Guidelines for Hazard
Assessment and Personal Protective Equipment Selection.
               - 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

                                                       33
     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 the
  “electric arc flash hazards”.


                                                                            34
1: NFPA 70E Standard for Electrical Safety in the Workplace, 2004 Edition
Why adhere to NFPA 70 E?




                           35
             January 9, 2002
 Conclusion:

 Though OSHA does not, per se, enforce NFPA 70E
  Standard, 2000 Edition, OSHA considers the NFPA
  Standard a recognized industry practice.

 The employer is required to conduct hazard
  assessment 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 require
  the employees to use the selected apparel.



                                                       36
           January 9, 2002
 Employers who conduct the hazard/risk
  assessment, and select and require their
  employees to use protective clothing and
  other PPE appropriate for the task, as stated
  in NFPA 70E 2000 edition, are deemed in
  compliance with the Hazard Assessment and
  Equipment Selection OSHA Standard

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




                                              37
                       OSHA
 OSHA commonly uses the “General Duty Clause”,
  which is paraphrased below or as an alternate
  uses NFPA 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”.
                                                          38
Why adhere to NFPA 70 E

           Answer


  It is the right thing to do!




                                 39
40
       Arc Flash Labels
              Question
What is and where are Arc Flash Label
             Required?




                                    41
              Arc Flash Labels
 Arc Flash labels are required on equipment “such as”
  panelboards, 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, equipment
  control panels and building management panels if they
  contain equipment that is 50 volts or higher and are
  “likely to require examination, adjustment, servicing or
   maintenance while energized”.




                                                             42
         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.
                                                          43
1. NFPA 70E 2009
      Arc Flash Hazard Labels
 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




                                                        44
       Arc Flash Hazard Labels
 Limited Approach: The closest distance an unqualified
  person can approach unless made aware of the danger
  and 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 the
  energy from the arc will not cause a 3rd degree burn to
  unprotected skin.

                                                            45
Arc Flash Hazard Labels




                          46
    Shock Hazard Analysis
         Electric Shock Hazard Analysis

 The following chart is the basis for
  determining electric shock boundaries. It is
  contained within NFPA 70 E 2009.

 The actual chart covers voltage as high as
  800,000 volts.




                                                 47
              Shock Hazard Analysis
 Table 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

               Limited Approach Boundary Restricted Approach
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.

                                                                               48
   Arc Flash Hazard Analysis

Arc Flash Hazard Analysis are performed
            to determine the

      Arc Flash Hazard Category

                 And

    Arc Flash Protection Boundary

                                     49
                     Arc Flash Labels
 Arc Flash Hazard Analysis. An arc flash hazard
  analysis shall determine the Arc Flash Protection
  Boundary 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
                                                      50
 1. NFPA 70E -2009
     Arc Flash Hazard Analysis
 Arc Flash Hazard Category – Is used to define
  the 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 suitably
  guarded, isolated, or insulated.1.

                                                      51
 1. NFPA 70E -2009
     Arc Flash Hazard Analysis
   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.)



                                                    52
 Reference – NFPA 70E – 2009 Appendix D
     Arc Flash Hazard Analysis
 Almost all arc flash analysis require knowing the
  available 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 the
  overcurrent 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 and
  Insulated and Insulating Hand Tools from NFPA 70E –
  2009 and selected footnotes for the Table are shown on
  the following slides.
                                                         53
       Arc Flash Hazard Analysis
           Table 130.7 (C)(9) from NFPA 70E - 2009
Task Performed on Energized Equipment               Hazard/Risk V-rated V-rated
                                                     Category   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   N
Circuit 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    N
Opening 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
                                                                         54
     Arc Flash Hazard Analysis
  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 the
  current limiting range of a current limiting fuse.


                                                             55
       Arc Flash Hazard Analysis
            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 without
       a 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.
                                                              56
       1. NFPA 70 E 2009
     Source of Power




57
Arc Flash Hazard Analysis




                            58
Arc Flash Hazard Analysis




      Who is Qualified?
                            59
                 Qualified Person
NFPA 70 E Standard for Electrical Safety in the Workplace,
                       2009 Edition

 Qualified persons permitted to work within the
 Limited Approach Boundary of exposed energized
 electrical conductors and circuit parts operating at 50
 volts 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.
                                                         60
                  Qualified Person
 NFPA 70 E Standard for Electrical Safety in the Workplace,
                        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 to
   determine the degree and extent of the hazard and
   the personal protective equipment and job planning
   necessary to perform the task safely
                                                          61
             Task Qualified Person
NFPA 70 E Standard for Electrical Safety in the Workplace,
                       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 at
 his 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.
                                                         62
                 Qualified Person
NFPA 70 E Standard for Electrical Safety in the Workplace,
                       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, including
 interpreting 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.




                                                         63
                 Qualified Person
NFPA 70 E Standard for Electrical Safety in the Workplace,
                       2009 Edition

 The employer shall document that each employee
 has received the training required. This
 documentation shall be made when the employee
 demonstrates proficiency in the work practices
 involved and shall be maintained for the duration of
 the employee’s employment. The documentation
 shall contain each employee’s name and dates of
 training.



                                                         64
           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 flash hazard analysis shall
not be required where all of the following conditions
exist:
(1) The circuit is rated 240 volts or less.
(2) The circuit is supplied by one transformer.
(3) The transformer supplying the circuit is rated less
than 125 kVA.
                                                     65
  Arc Flash Hazard Analysis
Therefore, there is NO requirement to
determine 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
                                           66
      Arc Flash Hazard Labels
 The following arc flash label would suffice in meeting the
  requirements of NEC Article 110.16 and NFPA 70E –
  2009.




                                                          67
 Arc Flash Hazard Analysis
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 second
 degree burn if an electrical arc flash were to
 occur”




                                                     68
Arc Flash Hazard Analysis

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 protective
equipment in accordance with 130.3. All parts of
the body inside the Arc Flash Protection Boundary
shall be protected.




                                               69
 Arc Flash Hazard Analysis
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 of
 an 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 balance
 between the calculated estimated incident energy
 exposure and the work activity being performed
 while meeting the following concerns:
                                                    70
  Arc Flash Hazard Analysis

a)The desire to provide enough protection to
  prevent a second degree burn in all cases.

b) The desire to avoid providing more
  protection than is needed. Hazards may be
  introduced by the garments such as heat
  stress, poor visibility, and limited body
  movement.”


                                           71
  Arc Flash Hazard Analysis
Without arc flash hazard analysis, which at a
minimum requires the determination of the
potential short circuit current and knowledge
of the overcurrent protective device, short of
testing, it is impossible to determine the
Incident Energy.

Therefore, without arc flash hazard analysis,
the only information that can be included on
label is the Required Level of PPE.

                                                72
  Arc Flash Hazard Analysis
NFPA 70 E does not define what is meant by
the “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 work
performed within the Arc Flash Protection
Boundary.




                                              73
  Arc Flash Hazard Analysis
Arc Flash Labels used to mark equipment for
which arc flash hazard analysis has not been
performed should indicate that the Level of
PPE shown on the label are
                “DEFAULT”
And

 “NO ARC FLASH HAZARD ANALYSIS WAS
            PERFORMED”
An Arc Flash Protection Boundary need not
be listed on the label.
                                            74
  Arc Flash Hazard Analysis
Considering that the hazard within the
equipment 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:


                                           75
  Arc Flash Hazard Analysis
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 Hazard
Category


                                                    76
 Arc Flash Hazard Analysis
Even if no Arc Flash Hazard
Category is defined, Safety glasses
or goggles and hearing protection
should be required for any
electrical work near exposed
energized parts except for circuits
originating from Class II power
sources as defined by Section 725
of the NEC.
                                  77
    Arc Flash Hazard Analysis

 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.




                                              78
        Arc Flash Hazard Analysis
Incident   Incident      FR
 Energy     Energy    Clothing         Clothing
  From       From      Class          Description
Cal/cm2    Cal/cm2      No.
                                 Non-melting, flammable
  0.0        1.2         0
                                       materials
  1.2        4.0         1       Arc Rated Shirt & Pants

  4.0        8.0         2       Arc Rated Shirt & Pants

                                 Arc Rated Shirt & Pants
  8.0       25.0         3
                                       & Arc Suit

                                 Arc Rated Shirt & Pants
 25.0       40.0         4             & Arc Suit



                                                           79
   Arc Flash Hazard Analysis
 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 or
  circuit parts.




                                          80
Arc Flash Hazard Analysis




   What are the formulas?


                            81
     Arc Flash Hazard Analysis
         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.
                                                           82
   Arc Flash Hazard Analysis
For Applications with system voltages below 1,000 Volts




where:
lg = the log10
Ia = arcing current in kA
K = -0.153 for open air arcs; -0.097 for arcs-in-a-box
Ibf = bolted three-phase available short-circuit current
(symmetrical rms) (kA) between 700 and 106,000 amps
V = system voltage in kV
G = conductor gap (mm) (See Table on following slide)

                                                           83
   Arc Flash Hazard Analysis
For applications with a voltage of 1,000 Volts or higher:




where:
lg = the log10
Ia = 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)


                                                            84
          Arc Flash Hazard Analysis
         Table D.8.2 Factors for Equipment and Voltage Classes
System                                           Typical
Voltage                                        Conductor                    Distance
  (kV)          Type of Equipment               Gap (mm)                   X-Factor
-------------------------------------------------------------------------------------------
                Open-air                            10–40                    2.000
0.208–1         Switchgear                             32                     1.473
                MCCs and panels                        25                     1.641
                Cables                                 13                     2.000
-----------------------------------------------------------------------------------------
                Open-air                             102                      2.000
   >1–5         Switchgear                         13–102                     0.973
                Cables                                13                      2.000
                Open-air                           13–153                     2.000
--------------------------------------------------------------------------------------
  >5–15         Switchgear                          153                       0.973
                Cables                               13                       2.000
                                                                                              85
   Arc Flash Hazard Analysis
For 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.”




                                                          86
     Source of Power




87
   Arc Flash Hazard Analysis
        Normalized Incident Energy Calculations:




where:
En = incident energy (J/cm2) normalized for time and
      distance
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)
                                                          88
   Arc Flash Hazard Analysis
     Converting 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 (working
     distance)
X = the distance exponent from Table on
     previous slide
                                                        89
   Arc Flash Hazard Analysis
              Flash 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.




                                                        90
   Arc Flash Hazard Analysis
                Flash 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
                                                                   91
     Arc Flash Hazard Analysis
 Equations for estimating incident energy and Flash
  Protection Boundaries based on statistical analysis and
  curve 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.



                                                          92
Arc Flash Hazard Analysis


             Question

What can be done to reduce arc flash
           exposure?




                                       93
     Arc Flash Hazard Analysis
               Design 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.
                                                        94
     Arc Flash Hazard Analysis
               Design 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
 switchgear
Apply overcurrent protective devices properly
Use circuit breakers with a maintenance instantaneous
 trip switch.
                                                             95
     Arc Flash Hazard Analysis
     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 circuit
voltage 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.

                                                               96
     Arc Flash Hazard Analysis
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 work
  is being performed
 Add optical sensors to trip when flash occurs
                                                           97
Flash Hazard Analysis




                        98
Arc Flash Hazard Analysis




                            99
Arc Flash Hazard Analysis




                            100
Arc Flash Hazard Analysis




                            101
     Arc Flash Hazard Analysis
 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 the
  transformers primary protection is very long for a fault on
  the secondary of the transformer.
                                                             102
Arc Flash Hazard Analysis




                            103
  Arc Flash Hazard Analysis

 Arc Flash Hazards can be reduced by current limiting
  fuses.

 The clearing time for a current limiting fuse is
  approximately ¼ cycle or 0.004 second. The clearing
  time 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 safety
 margin of 2 cycles, giving a total time of approximately
 6 cycles.
                                                      104
     Arc Flash Hazard Analysis
Arc Flash Hazards can be reduced by: Current Limiting
Fuses and Cable Limiters




                                                        105
     Arc Flash Hazard Analysis
Arc Flash Hazards can be reduced by: Current Limiting
Fuses and Cable Limiters




                                                        106
    Arc Flash Analysis




            Question
What is required to do an arc flash
           analysis?
                                      107
              Arc Flash Analysis
 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 in
    the Workplace, 2004 Edition


                                                           108
                    Arc Flash Analysis
                    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 each
   branch for each fault location.


                                                                109
1. Arc Flash User’s Guide – SKM Power Systems, Inc.
                    Arc Flash Analysis
                    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 voltage
     and equipment class.

  7. Calculate the incident energy at each fault location.

  8. Calculate the flash protection boundary at each fault
     location.

                                                             110
1. Arc Flash User’s Guide – SKM Power Systems, Inc.
        Overall Benefits

              Question

What are the overall benefits of an arc
           flash analysis?




                                      111
              Overall Benefits
            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!
                                                          112
                 Overall Benefits
       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.
                                                          113
             Arc Flash Summary
 Proper Maintenance

    Define and follow necessary PM procedures

 Knowledge

    Understand the true dangers of electricity

 Planning

    Develop and follow a work plan that includes
     identifying the arc flash hazard

    STAY ALERT – STAY WELL – STAY ALIVE
                                                    114
                                                  Questions?
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

                                                  www.MaidaEngineering.com

                            Joseph Maida
                                 President
                              215.542.8700 x141
                           jmaida@maidaeng.com

				
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