arc flash & ppe update...ground fault - energized conductor making an unintentional contact with...
TRANSCRIPT
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 [email protected]
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Questions?
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