ARC FLASH & PPE UPDATE

Michael Olivo, P.E.

Aaron Ramirez, E.I.T.

What is Arc Flash?

Arc Flash is the release of heat and light

produced when electrical current flows through

an air gap between two conductors

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Overview of Arc Flash

What is Arc Flash?

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Arc Fault An arc fault is when air separation between high

voltage conductors is compromised allowing

electrical current to flow through the air gap

between conductors

Air separation is compromised by insulation

breakdown or accidental contact with the electrical

systems

Arc fault creates an electrical explosion

Light and heat emitted from the explosion is known

as arc flash

Pressure wave caused by the tremendous

temperatures of the arc flash is known as arc blast

Electrical explosion

Arc Flash Arc BlastArc Flash

Arc Flash and Arc Blast

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Temperatures can reach 35,000◦F

Exposure to these extreme

temperatures burns the skin and

causes clothing to catch on fire

Arc flash will kill up to distances of

10 ft.

Explosive expansion of the air and metal in the arc path

Dangers associated with expansion are high pressure waves, sound, and shrapnel

Heated metal is expelled away from the arc at speeds exceeding 600 mph

Arc Blast

Arc Flash

What causes an Arc Flash?

Short Circuit - energized conductor making an unintentional contact with another energized conductor

Ground Fault - energized conductor making an unintentional contact with ground

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Dropped screw touching 240V and Ground (Ground Fault)

Screwdriver touching 240V and 240V (Short Circuit)

240V 240V

240V 240V

0V

0V

The following events will create an arc flash

Insulation breakdown

Accidental contact with the electrical systems

Improper use of tools

Dropped tools

Corrosion

Lack of electrical safety training

Lack of preventative maintenance

What is incident energy?

Incident energy is the temperature

produced (in cal/cm²) at a

distance (usually eighteen inches)

from an arc flash

Hand 1 inch over flame for 1

second equals 1 cal/cm²

It takes 1.2 cal/cm² to create a

second-degree burn

A second-degree burn causes skin

to blister and become sore

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1 Cal/cm2

1.2 Cal/cm2

PPE Categories

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Personal Protective Equipment (PPE)

PPE Category 0

If incident energy < 1.2 cal/cm^2

Use PPE Category 0

Untreated Cotton Long Sleeve Shirt, Pants,

Safety glasses, Hearing Protection

Number one question asked, "What level of

PPE should we use?”

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Note: (*) While the 2015 NFPA 70E Edition no longer recognizes Category 0 as an

“arc flash” hazard, the need for proper personal protective equipment (PPE)

remains unchanged.

Two ways to evaluate Arc Flash

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Arc Flash StudyTables in NFPA 70E

Table Method

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Table 130.7(C)(15)(A)(a)

Table 130.7(C)(15)(A)(b)

Table 130.7(C)(15)(A)(a)

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Table 130.7(C)(15)(A)(a)

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Table 130.7(C)(15)(A)(b)

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Table 130.7(C)(15)(A)(b)

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Arc Flash study

How it works

We send this form to the District

District fills out the form with

information from the field

District sends back the form to us

We will run it in our arc flash

calculation software

We will print the equipment labels

and send back to the District to put

on the equipment

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Arc Flash study

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City

Location

GPS coordinates

Transformer rating

Service Drop

Conductor sizes

Conductor lengths

Conductor type

Overhead/Underground

Service Entrance

Conductor sizes

Conductor lengths

Conductor type

Arc Flash study

Meter

Company

Meter Code

Barcodes

Service

Breaker brands

Breaker sizes

Breaker labels

Service Information

Manufacture

Service Code

Line voltage

Date of manufacture

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Arc Flash study

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Signal Cabinet Feeder

Conductor sizes

Conductor lengths

Signal Cabinet

Breaker brands

Breaker sizes

Breaker labels

Results from skm

Results from US 290 and George Bush

St

At the electrical service incident energy

is 3.4 Cal/cm2

PPE Category 1 will be required

At the Controller the incident energy is

0.1 Cal/cm2

PPE Category 0 will be required

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Intersection Example 1

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5.69 Cal/cm^2

PPE Level 2

1.48 Cal/cm^2

PPE Level 1

Intersection Example 2

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1.72 Cal/cm^2

PPE Level 1

0.34 Cal/cm^2

PPE Level 0

Intersection Example 3

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0.71 Cal/cm^2

PPE Level 0

0.36 Cal/cm^2

PPE Level 0

The 3 locations shown are all traffic signals and all have similar configurations but have different incident energy values

There is no discernable pattern in arc flash

We can’t control transformer size

We can’t control distance between electrical service and traffic signal controller on existing locations

Things we can CHANGE are size of breakers and the size of conductors

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Any Pattern seen in Arc Flash Study?

Will that help?

Design circuit with smaller breakers

Design circuit with smaller conductors

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Design

Use Smaller Breakers

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2P/60 A

0.1 Cal/cm^2

PPE Level 0

2P/70 A

1.7 Cal/cm^2

PPE Level 1

Use Smaller Wire Sizes

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8 AWG

0.5 Cal/cm^2

PPE Level 0

4 AWG

1.5 Cal/cm^2

PPE Level 1

Smaller Conductor Sizes and Arc Flash

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Reducing conductor size reduces the incident energy

8.39% cost savings replacing #4 conductor with #6 conductor

17.87% cost savings replacing #4 conductor with #8 conductor

Any Hidden Costs?

Theft deterrent

Smaller conductor size makes

criminals less likely to steal and

easier on our budget to replace.

Summary

Arc Flash is the release of extreme heat and light

Two ways to evaluate Arc Flash - Tables in NFPA 70E or performing Arc Flash

Study

Arc flash hazard decreases when breaker and conductor sizes are reduced

Cost Savings

Direct ALL QUESTIONS related to purchasing PPE to Sidney Maloy (512) 416-

3318 Sidney.Maloy@txdot.gov

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Questions?

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