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Arc FlashTechnical

Perspective

Jim Phillips, P.E.

Arc Flash and the Technical Perspective

● Vice Chair of IEEE 1584 IEEE Guide for Performing Arc Flash Hazard Calculations● International Chair of Geneva Based IEC TC78 Committee – Live Working● Liaison Officer between IEEE 1584 and IEC TC78 Arc Flash Committees● Author of the book: Complete Guide to Arc Flash Hazard Calculation Studies● Member: Steering Committee – IEEE/NFPA Arc Flash Collaborative Research Project● Founder of the Electrical Power and Electrical Safety Training Company: Brainfiller.com● Founder of the internationally known website: ArcFlashForum.com

Jim Phillips will discuss the relevant OSHA, NESC and IEEE standards used for protecting workers from the arc flash hazard. See how to create an arc flash protection strategy by determining the severity of the thermal hazard and specifying suitable arc rated clothing and related personal protective equipment. Jim is at the forefront of arc flash standards both nationally and internationally and is:

Major Standards

Electrical Safety Pyramid

OSHAFederal

Regulations

Consensus Standards

NFPA 70E - General Industry

NESC - Electric Utility

Guides, Practices, Methods

IEEE 1584 - IEEE Guide for Performing Arc Flash Hazard Calculations

OSHA 1910.269(I)(8)(ii)

Clothing Restrictions

• The employer shall ensure that

each employee who is

exposed to the hazards of

flames or electric arcs does not

wear clothing that, when

exposed to flames or electric

arcs, could increase the extent

of injury that would be

sustained by the employee.

OSHA 1910.269(I)(8)

• Assess workplace for hazards from flames or

electric arcs

• If there is exposure, estimate incident energy

• Appendix E provides methods for estimating Ei

• Other methods could be used if reasonable

• Require Arc Rated clothing under certain

conditions

• Select clothing with arc rating grater than

estimated incident energy

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• Intensity

• Duration

• Distance

• Equipment Type

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• ATPV or Ebt

• Arc Rating is on

the Garment Label

• cal/cm2

• J/cm2

• kJ/m2

Higher Short Circuit + Longer Clearing Time

= Greater Incident Energy

How much short circuit current?

Arc Flash Duration?

Protective device

opening time?

Arc Flash Duration and Incident Energy

Incid

en

t E

ne

rgy –

ca

l/cm

2

0

2

4

6

8

10

12

3 6 9 12

Clearing Time - cycles

Selecting a Reasonable Incident Energy

Calculation Method

• IEEE 1584 Calculations - 3 Phase• Good for equipment in enclosures

• Empirical < 15 kV

• Theoretical > 15 kV

• OSHA 1910.269 Appendix E Tables

• NESC Tables 410-1 and 410-2

• Arc Pro - 1 Phase

IEEE 1584 – IEEE Guide for Performing

Arc-Flash Hazard Calculations

• Calculations based on IEEE working group

• Calculations are still evolving

• Based on statistical analysis and curve fitting

• Calculations for incident energy limitations• Voltage 208 Volts to 15 kV three phase

• 50 to 60 Hz.

• 700 Amps to 106,000 Amps short circuit

• 13 mm to 152 mm conductor gap

• Intended for three phase - Conservative if

single phase event

PPE / Arc Rating Selection from Study

Results Using IEEE 1584 Calculations

Arc Flash Calculation Study ResultsBrainfiller Industries

Bus NameVoltage

(kV)Equipment

TypeArc Gap

(mm)

Bolted Fault (kA)

Est. Arc Fault (kA)

Arcing Time (sec)

Est. Arc Flash

Boundary (feet)

Working Distance (inches)

Incident Energy

(cal/cm2)PPE Level

MAINSWGR

0.48 Switchgear 32 37.734 19.034 0.167 6.65 24 7.0 #2

PANEL 1A 0.48 Panel 25 27.285 15.457 0.200 5.67 18 10.6 #3

PANEL 1B 0.48 Panel 25 27.368 15.497 0.050 2.13 18 2.7 #1

MCC-1 0.48 MCC 25 21.117 12.418 0.100 2.81 18 4.2 #2

PANEL 2 0.48 Panel 25 21.164 12.442 0.033 1.44 18 1.4 #1

Incident Energy in cal/cm2

2017 NESC Rule 410.A.3Paraphrased

Performed by: Wylie E. Coyote

Reviewed by: Road Runner

Employer shall ensure assessment is

performed to determine arc flash hazard

Perform a detailed arc hazard analysis or

use Table 410-1, 410-2 or 410-3

Analysis includes calculation of estimated

arc energy

Employees wear clothing or clothing system

with effective arc rating not less than

anticipated level of arc energy.

Exception: If clothing can create a greater

hazard then an arc rating less than required

may be worn

NESC Table 410-1 Clothing and clothing

systems for 50 V to 1000 V (ac)

Equipment TypeNominal Voltage Range and cal/cm2

50 V to 250 V 251 V to 600 V (14) 601 V to 1000 V

Self-contained meters / cabinets 4 (2) 20 (4) 30 (8)

Pad mounted transformers 4 (9) 4 (9) 6 (8)

CT meters and control wiring 4 (2) 4 (5) 6 (8)

Metal-clad switchgear / motor

control centers8 (3) 40 (6) 60 (8)

Pedestals / pull boxes / hand

holes4 (2) 8 (7) 12 (8)

Open air (includes lines) 4 (2) 4 (7) 6 (8)

Network protectors 4 (10) (11) (11)

Panel boards – single phase (all) /

three phase ( 100A)4 (2) (13) (13)

2017 National Electrical Safety Code – always consult the latest editionNote: Use the NESC table

NESC Table 410-1

Notes – Partial List

1) Developed from fault testing based on equipment type and is

independent of fault current unless otherwise noted.

2) Industry testing shows arc does not sustain more than 2 cycles

3) Based on IEEE 1584 equations. 1 inch gap, 1.641 distance

factor, 208V, 1000 kVA transformer, 500 MVA source, max

duration 10 cycles

4) Industry testing did not exceed 20 cal/cm2

5) Industry testing did not exceed 4 cal/cm2

6) Based on IEEE 1584 equations. 1 inch gap, 1.641 distance

factor, 480 V, 12.47 kA, max duration 85 cycles

7) Incident analysis does not exceed table values

8) Engineering analysis shows using 150% multiplier is conservative

9) Industry testing shows values do not exceed 4 cal/cm2

2017 National Electrical Safety Code – Consult the standard for the complete list. Always consult the latest edition

NESC Table 410-1

Notes – Partial List

10)Industry testing shows values do not exceed 4 cal/cm2

11)Industry testing shows arc will not self extinguish and heat flux

rates will exceed 60 cal/cm2/second at 24 inch working

distance – perform analysis.

12)Industry testing shows values do not exceed 8 cal/cm2

13)Industry testing shows arc will not self extinguish and heat flux

rates will exceed 60 cal/cm2/second at 18 inch working

distance – perform analysis.

14)IEEE 1584 original test data indicates there is no significant

difference between heat flux rates for 400V class and 600V

class equipment.

2017 National Electrical Safety Code – Consult the standard for the complete list. Always consult the latest edition

Transformer Secondary Blind Spot

Forensic Analysis

Sleeve burned through

Leather burned through, rubber

line is intact

Example of an arc rated FR shirt (5 - 6 cal/cm2) and

gloves worn by a person who was burned in a

secondary fault while hooking up some 120/208V.

leads to a pad mounted transformer. He came out

of it with just some 2nd degree burns on his arm.

Arc Rated Clothing and PPEC

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NFPA 70E 130.7(C)(10) (b)(1)

Head Protection < 12 cal/cm2

Arc rated face shield with

arc rated balaclava for

head protection when head

is within arc flash boundary.

Arc rated hood is permitted

instead of face shield and

balaclava

NFPA 70E 130.7(C)(10) (b)(2)

Head Protection > 12 cal/cm2

When the incident energy

exposure is greater than 12

cal/cm2, an rated hood shall

be used.

Head Protection

OSHA 1910.269(i)(8)(v)(C) thru (E)

1910.269(l)(8)(v)(C)

Arc-rated protection is not necessary for the employee's head when the employee is

wearing head protection meeting § 1910.135 if the estimated incident energy is less

than 9 cal/cm2 for exposures involving single-phase arcs in open air or 5 cal/cm2 for

other exposures,

1910.269(l)(8)(v)(D)

The protection for the employee's head may consist of head protection meeting §

1910.135 and a faceshield with a minimum arc rating of 8 cal/cm2 if the estimated

incident-energy exposure is less than 13 cal/cm2 for exposures involving single-

phase arcs in open air or 9 cal/cm2 for other exposures, and

1910.269(l)(8)(v)(E)

For exposures involving single phase arcs in open air, the arc rating for the

employee's head and face protection may be 4 cal/cm2 less than the estimated

incident energy.

Face Protection

Face shields must have

sufficient arc rating and a

wrap-around guarding to

protect the face, chin,

forehead, ears and neck.

Hand Protection

Heavy duty leather gloves or

arc-rated gloves shall be worn

Leather protectors shall be worn

over rubber insulating gloves.

Clothing Material Characteristics

• Non-AR fabrics that ignite

(start to burn) will continue

to burn and can increase

the severity of the burn.

• AR fabric can ignite but will

extinguish itself after the

ignition source is gone.

• AR materials provide

thermal protection.

NFPA 70E

130.5(H) Equipment Labeling

130.5(H)(1) Nominal system voltage

130.5(H)(2) Arc flash boundary

130.5(H)(3) At least one of the following:

Incident Energy and Working Distance Selected

Thank You!

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