Arc Flash Protective

Gear

Personal Safety in Performing

Stray Voltage Investigations

by Tom Seidl

We Energies

Arc-Flash Hazard

• 5-10 incidences occur every day

• Burns

• Hot Gases can injure lungs and impair

breathing

• Hot Copper/metal

• Blast Pressure

General Duty Clause

Section 5(a)(1)

Requires an employer to

provide an employee with a

workplace free from

recognized hazards.

OSHA 29 CFR 1910.132(d)(1)

• Requires employers to evaluate hazards

• Requires employers to select and require

use of PPE for employees.

Details are left to Consensus

Standards

• NFPA 70

• NFPA 70E

• ANSI

• ASTM

• IEEE

NFPA 70E Covers

• Public and private premises

• Yards, lots, carnivals, parking lots and

industrial substations

• Installations of conductors & equipment

that connect to the supply of elecricity

• Installations used by the electric utility

….that are not an integral part of a

generating plant, substation, or control cntr.

NOT Covered:

Installations under exclusive control

of an electric utility where such:

• Consist of service drops or service laterals

& associated metering

• Are located in …easements or rights-of-way

recognized (as under jurisdiction of a utility

commission)

• Are on property owned by the electricity

utility for the purpose of …distribution of

electric energy

NESC 410

• Assessment of the system is required.

• If >2 cal/cm2, clothing system adequate for the anticipated level of arc energy.

• For voltages >1000 Volts, effective arc rating of clothing system determined from Table 410-1 & 410-2 or Arc Flash Analysis

Systems Below 1000 Volts

• Engineering controls to limit exposure.

• Clothing system with a minimum 4

cal/cm2

Generally, when you go to work on a

farm, even though you are a utility

employee, your are governed by

NFPA 70 E

Best Practice - De-energizeNFPA 70E Article 130.1: All equipment and

circuits shall be put into an electrically safe

condition before working within the Limited

Approach Boundary unless:

• Doing so presents a greater hazard

• Infeasibility

• Less than 50 Volts

FPN No. 2

Examples that might be

performed w/i the Limited

Approach Boundary … because

of infeasibility …include

performing diagnostics and

testing (e.g., troubleshooting)

Arc Flash Hazard Analysis(Required: NFPA 70E, Article 130.30)

• Determine the Arc Flash Protection Boundary

• Determine the personal protective equipment that people within the Arc Flash Protection Boundary shall use.

Incident Energy

The amount of energy

(cal/cm2) impressed on a

surface, a certain distance

from the source, generated

during an electrical arc event.

Flash Protection Boundary

An approach limit at a

distance from exposed live

parts within which a person

could receive a 2nd degree

burn if an electrical fault were

to occur. (1.2 cal/cm2)

Flash Hazard Analysis (130.3)

For systems 600 Volts or less, the

flash protection boundary shall be

4 feet. (Assumes 2 cycle clearing

time and 50 kA ASCC or any

combination not exceeding 100

kA Cycles.

The incident energy exposure level

shall be based on the working

distance of the employee’s face and

chest areas from a prospective arc

source for the specific task to be

performed.

Article 130.3, 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 of less.

2. The circuit is supplied by one transformer.

3. The transformer supplying the circuit is

rated less than 125 kVA

Equation of Arc in a Cubic Box

• DB = distance from arc electrodes, inches (for distances 18

in. and greater)

• tB = arc duration, seconds (cycles/60 cycles)

• F = bolted fault short circuit current, in kA (for the range

of 16 to 50 kA)

• EMB = 1038.7 x DB-1.4738 x tA x (0.0093 x F2 – 0.3453 x F +

5.9675)

• EMB = maximum 20 in cubic box incident energy

Equation of Arc in Open Air

• DA = Distance from arc electrodes, inches (for

distances 18” and greater.

• tA = arc duration, seconds (cysles/60 cycles)

• F = bolted fault short circuit, in kA (for the range

of 16 to 50 kA)

• EMA=5271 x DA-1.9593 x (0.0016 x F2 – 0.0076 x F

+ 0.8938)

• EMA = maximum open arc incident energy in

calories/cm2

Arc Flash Protection (transformer)

Boundary

• MVA = rating of transformer

• t = time of arc exposure in seconds, (cycles/60

cycles)

• DC = (53 x MVA x t)1/2

• DC = Curable Distance

Arc Flash Protection (bolted fault)

Boundary• MVAbf = bolted fault MVA at point involved

• V = Volts

• %Z = percent impedance based on transformer MVA

• T = time of arc exposure in seconds, (cycles/60 cycles)

• ISC = (((MVA Base x 106)/(1.732 x V)) x 100/%Z)

• ISC = Short Circuit Current

• P = 1.732 x V x ISC 10-6 x 0.7072

• P = maximum power (in MW) in a 3 phase arc

• DC = (2.65 x MVAbf x t)1/2

• DC = Curable Burn Distance

The incident energy should

be calculated at the

maximum and at 85 % of

maximum arc fault. (A

longer clearing time can

result in more incident

energy.

Flash Hazard Analysis (130.3)

As an alternative, the PPE

requirements of 130.7(C)(9) shall be

permitted to be used in lieu of the

detailed flash hazard analysis

of 130.3A

600 Volt MCC’s

Arc Rating of a Material

• Maximum incident energy resistance prior

to breakopen or onset of 2nd degree burns.

• cal/cm2

• Break open - formation of 1 or more

holes in the innermost layer.

Clothing made from nonmelting

flammable natural materials such

as cotton, wool, rayon, or silk is

permitted for Hazard/Risk

Category 0 if flash hazard is <1.2

cal/cm2

Underlayers

Meltable fibers are not

permitted.

(an incidental amount of

elastic is permitted.)

Acetate, acrylic, nylon,

polyester, polyethylene,

polypropylene, and spandex,

either alone or in blends,

shall not be used.

• FR clothing is required to be work within

the Flash Protection Boundary, which is

generally considered to be 1.2 cal/cm2

• FR clothing for race car drivers or pilots is

not suitable for arc flash protection. Arc

rated FR clothing is the only FR clothing

marked with the cal/cm2 rating.

Clothing and other apparel (hair nets, hard hat liners) made from materials that do not meet the requirements of 130.7(C)(14) regarding melting, or made from materials that do not meet the flammability requirements shall not be permitted.

Foot Protection

• Shoes with an arc rating are not available.

• Foot Protection. Heavy-duty leather work shoes

provide some arc flash protection to the feet and

shall be used in all tasks in Hazard/Risk Category

2 and higher and in all exposures greater than 4

cal/cm2.

• An incidental amount of elastic used on

nonmelting fabric underwear or socks shall be

permitted.

Hands

• No method exists for determining the

degree of exposure for a worker’s hands.

• Leather of FR gloves shall be worn where

required for arc flash protection.

• Where insulating rubber gloves are used for

shock protection, leather protectors shall be

worn over the rubber gloves.

Safety glasses must be

worn under the face

shield or viewing

window.

Outer Layers

Garments worn as outer

layers over FR clothing,

(jackets or rain wear) must

also be FR clothing.

Exposure of more than 40

cal/cm?

• task must not be performed until and electrically safe work condition exists

• FR clothing with a very high incident energy rating might me needed to perform the steps necessary to establish an electrically safe condition

• This is the only task that should be accomplished with the equipment energized

• Inspection

• Manufacturer’s Instructions.

• Storage

• Cleaning

Care and Maintenance of FR

Clothing and FR Arc Flash Suits

Other Personal Protective

Equipment

• Eye protection

• Head protection

• Conductive Articles not worn

• Face shields w/o Arc rating shall not be

used.

• Eye protection always be worn under face

shields or hoods.

15 cal/cm2

25 cal/cm2

40 cal/cm250 cal/cm2

Proper PPE

• Does not guarantee the worker will remain

injury free

• The purpose is to reduce death

• Burns to the hands and arms aren’t

considered life threatening

Insulated Tools

Employees shall use

insulated tools and/or

handling equipment when

working inside the limited

approach boundary.(Must be marked with a voltage rating.)

The best solution is to

always do as much work as

possible with the system

de-energized.

Alternatives During SV

Investigations

• Know the maximum fault current at the farm

where you are working.

• Measure line voltages at receptacles

• Open panels only when de-energized

• Connect the “panel neutral” lead to the grounding

electrode conductor externally from the

panelboard

• Access the panel neutral at remote panels through

contact with the equipment grounding conductor

at a nearby receptacle

Practices

• Measure at the lowest energy point

(smallest breaker)

• If you can, keep both hands free

• 1 PH measurements - connect neutral first

and remove last

• Three point method

• Use probes with minimum exposed metal

• Keep on hand in your pocket.

Table 130.7(c)(9)(a)

requires you to know the

bolted fault level and

approximate fault

clearing time.

VPRIMARY = ?% Of Normal

Transformer Impedance Measurement

Ifull load current

+

-

That percentage is the percent Impedance (%Z)

VPRIMARY = Normal

Transformer Available Short Circuit Current

IShort Circuit

+

-

ASSC = Ifull load current / %Z

100

OH XFMR Size Sec. Volt. FL Amps %Z ASSC

15 120/240 62.5 1.5 4166

25 120/240 104 1.5 6933

50 120/240 208 1.5 13867

100 120/240 417 2 20850

167 120/240 696 2 34800

Other

Rules

Equipment Contact

Employees standing on the

ground shall not contact the

vehicle or mechanical

equipment or any of its

attachments.

Equipment Grounding

Barricade or insulate to

protect employees from

hazardous step and touch

potentials.

Set-up

• Assess the environment

• do not work alone

• Wear appropriate PPE - NFPA 70E

• Test Instruments - rated for environment

(CAT III or CAT IV)

• Know how to use the equipment

Prohibited Approach Boundary

An approach limit and a

distance from an exposed live

part within which work is

considered the same as

making contact with a live

part.

Restricted Approach Boundary:

An approach limit at a distance from

an exposed live part within which

there is an increased risk of shock,

due to electrical arc-over combined

with inadvertant movement, for

personnel working in close proximity

to the live parts.

Limited Approach Boundary

An approach limit at

distance from an exposed

live part within which a

shock hazard exists.

Shock Hazard Analysis