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Electrical Safety

Tony Locker, P.E.

Littelfuse513-693-5956

tlocker@littelfuse.com

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Learn:

� Reasons for Reducing Risk of Arc-Flash Hazards

� OSHA’s position on Arc Flash Hazards

� How to use Hierarchies to prioritize Design Techniques and Products that can lower hazards and increase safety

– Current-Limiting fuses

– High-Resistance Grounding Systems

– Arc-Flash Relays

– Arc-Resistant safety products

Goals of Presentation

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Learn:

� Reasons for Reducing Risk of Arc-Flash Hazards

Goals of Presentation

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Arc Flash / Blast Statistics

� Over 1000 people die each year from electrical accidents*

Up to 10 Arc-Flash incidents occur each day in the US

Over 2000 workers are sent to burn centers each year with severe Arc-Flash burns.

� OSHA states that 80% of electrically related accidents and fatalities among Qualified Workers are caused by Arc-Flash/Arc-Blast Incidents.

* Source: National Safety Council

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� Severe burns

� Vision damage or blindness

� Hearing loss

� Broken bones or internal organ damage

� Whiplash

� Brain injuries

� Lacerations

� Fatality

Photos courtesy of OSHA

Effects of Electrical Hazards on Workers

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Costly Damage…

� Equipment replacement and need for capital

� Equipment repair costs

� Downtime

� Production Loss (scrap)

…and business interruption.

Image from IEEE Electrical Safety Workshop, Floyd, Doan, Barrios, Wellman

Image from IEEE Electrical Safety Workshop, H. Landis Floyd, II

Effects of Electrical Hazards on Business

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Learn:

� Reasons for Reducing Risk of Arc-Flash Hazards

� OSHA’s position on Arc-Flash Hazards

Goals of Presentation

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What’s OSHA’s position on Arc-Flash Hazards?

In a letter of interpretation dated 11/14/2006,

OSHA states,

““““OSHA recommends that employers consult OSHA recommends that employers consult OSHA recommends that employers consult OSHA recommends that employers consult consensus standards such as NFPA 70Econsensus standards such as NFPA 70Econsensus standards such as NFPA 70Econsensus standards such as NFPA 70E----2004 to identify safety measures that can be 2004 to identify safety measures that can be 2004 to identify safety measures that can be 2004 to identify safety measures that can be used to comply with or supplement the used to comply with or supplement the used to comply with or supplement the used to comply with or supplement the requirements of OSHA's standards for requirements of OSHA's standards for requirements of OSHA's standards for requirements of OSHA's standards for preventing or protecting against arcpreventing or protecting against arcpreventing or protecting against arcpreventing or protecting against arc----flash flash flash flash hazardshazardshazardshazards…”…”…”…”

Source: http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=25557

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� The de facto “How to” standard to meet OSHA regulations.

� The industry preferred consensus standard to assess electrical hazards and implement safe work practices.

� Establishes Shock and Arc-Flash Protection Boundaries

� Determines Hazard Risk Categories and required Personal Protective Equipment

� Complies with OSHA and all state occupational safety organizations

NFPA 70E, Standard for Electrical Safety in the Workplace:

NFPA is a registered trademark of the National Fire Protection Association (NFPA), Quincy, MA.

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Arc-Flash Statistics

A major diversified chemical company* studied 91 facilities with over 19,000 buses. Figure 3 shows the percentage of buses found from 0 to over 100 cal/cm2

* IEEE Paper No. PCIC-2007-40

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Learn:

� Reasons for Reducing Risk of Arc-Flash Hazards

� OSHA’s position on Arc-Flash Hazards

� How to use Hierarchies to prioritize Design Techniques and Products that can lower hazards and increase safety

Goals of Presentation

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Hierarchy of Controls – OSHA and ANSI Z10

1. Engineering Controls –Seek to eliminate the hazards at the source.

2. Safety/Process Controls –Can not eliminate hazard …reduce the hazard and/or worker exposure to hazardous conditions.

3. PPE Controls – Devices and clothing worn by workers to safeguard themselves against the hazards

1. Elimination – Design to eliminate hazards

2. Substitution – Substitute or reduce the hazard

3. Engineering – Equipment modifications, etc

4. Administration – Procedures, Training, etc

5. Personal Protective Equipment – Safety glasses, face shields, gloves, etc

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Hierarchy of Controls – OSHA and ANSI Z10

E5.1.2: The hierarchy provides a systematic way to determine the most effective feasible method to reduce risk associated with a hazard.When controlling a hazard, the organization should first consider methods to eliminating the hazard or substitute a less hazardousmethod or process. … This process continues down the hierarchy until the highest-level feasible control is found.

Often, a combination of controls is most effective. In cases where the higher order controls (elimination, substitution, and implementation of engineering controls) do not reduce risk to an acceptable level, lower order controls (e.g. warnings, administrative controls, or personal protective equipment) are used to complement engineering controls to reduce risks to an acceptable level.

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Learn:

� Reasons for Reducing Risk of Arc-Flash Hazards

� OSHA’s position on Arc Flash Hazards

� How to use Hierarchies to prioritize Design Techniques and Products that can lower hazards and increase safety

– Current-Limiting fuses

Goals of Presentation

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What is Current Limitation?

� Article 240.2 of the National Electrical Code (NEC) states that a current limiting overcurrent protective device when operating in its current-limiting range, reduces the current in a faulted circuit to a value substantially less than the current which would occur if the current limiting device were not in the circuit.

� A current limiting device is one that opens and clears a fault within the first half cycle. One half cycle of standard 60 Hz current is equivalent to .00833 second (8.3 msec.)

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Current limiting overcurrent protective devices reduce the total destructive heat energy(I2t) to the circuit and it’s components to a small fraction of the energy available in the system. This is represented by the colored, shaded areas above.

Current Limitation

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Effect of Upgrading Fuses

Class RK5

Class RK1

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Learn:

� Reasons for Reducing Risk of Arc-Flash Hazards

� OSHA’s position on Arc Flash Hazards

� How to use Hierarchies to prioritize Design Techniques and Products that can lower hazards and increase safety

– Current-Limiting fuses

– High-Resistance Grounding Systems

Goals of Presentation

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Initiators of Electrical Faults

� IEEE Std 493-1997 (Gold Book) Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems

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Breakdown of Electrical Faults

Current-limiting fuses reduce hazards on

3-phase faults

* Source: Industrial Power System Grounding Design Handbook by J.R. Dunki-Jacobs, F.J. Shields and Conrad St. Pierre

HRG Systems prevent all hazards

associated with ground faults !

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Resistance Grounded Systems vs Solidly-Grounded Systems

IEEE Std 141-1993 (Red Book) Recommended Practice for Electric Power Distribution for Industrial Plants

7.2.2 There is no arc flash hazard, as there is with solidly grounded systems, since the fault current is limited to approximately 5A.

Another benefit of high-resistance grounded systems is the limitation of ground fault current to prevent damage to equipment. High values of ground faults on solidly grounded systems can destroy the magnetic core of rotating machinery.

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Convert to High Resistance Grounded (HRG) System

� By adding a power resistor between the common terminal and Ground, a HRG System is created.

� Advantages of HRG Systems– No Arc Flash Hazards during first ground fault

– No shutdown during first ground fault

– No transient over-voltages

– Ability to locate ground faults

� Disadvantages– Workers must be trained on system

Source(Wye)

HRG CØ

BØAØ

N

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277VLG

277VLG

277VLG

~0VNG

Normal Operation – Low Voltage Resistance Grounding

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480VLG

480VLG

0VLG

277VNG

2 ways to Detect Ground Fault on RG System –Voltage and Current

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Resistor

Failure

Loose

Connection

Corrosion

Broken or

Grounded Wire

Stolen Wire(s)

Why monitor the resistor?

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L

oad

Ground-Fault Relay

Failed Resistor - Impact on System

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L

oad

Ground-Fault Relay

Failed Resistor – Impact on System

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Failed Resistor – Impact on System

No Indication of a Ground Fault

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New approach to NGR Monitoring

CT is used to monitor ground-fault current Continuously monitors

resistance using sensing resistor in parallel with NGR

NGR

R

N

G

Voltage at the neutral is monitored

A voltage clamp in the sensing resistor eliminates hazardous voltage levels at the relay

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Learn:

� Reasons for Reducing Risk of Arc-Flash Hazards

� OSHA’s position on Arc Flash Hazards

� How to use Hierarchies to prioritize Design Techniques and Products that can lower hazards and increase safety

– Current-Limiting fuses

– High-Resistance Grounding Systems

– Arc-Flash Relays

Goals of Presentation

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� Typical Arc-Flash Relay

– 1ms reaction time

� Detects light

– Point sensors

– Fiber optic sensor

� Detect over-currents

– Phase CTs (3)

� Link AF Relays

– Larger systems

Breakthroughs in Arc Flash Relay Technologies

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Lifespan of an Arc Fault

1.1.

2.2.

3.3.

4.4.

5.5.

6.6.

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Lifespan of an Arc Fault

t (ms)

Arc

En

erg

y (

I2t,

kA

2s)

100 4000 200

Ste

el F

ire

Cab

le F

ire

Cop

per

Fire

Total breaking time with PGR-88001 + (35…60) ms

50 kA bolted fault between 480 Vac and ground

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Examples of Arc Faults

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Typical Wiring Diagram of an Arc-Flash Relay

TripCoil

L1 L2 L3

5A CTs

Inhi

bit

Trip

Res

et

To next PGR-8800

Three-phaseOvercurrent Protection

To next PGR-8800

100-240 Vac/Vdc

GND

12-48 Vdc+ -

Battery (24 VDC)

Positive Bus

Negative Bus

-

Trip Voltage24 - 600 VDC24 - 440 VAC

Up to 6 Point or Fiber Optic Sensors with built-in circuit-check

PC withMicrosoft Windows®

Config, log &firmware upgrade

USB

Online Service Tripped

OutputsInputs

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Point Sensors

Red LED forCircuit-check& Visual Diagnostics

MountingHoles(front / back)

32 mm

52 m

m

8 mmSensor

Lens

Ø3.5 mm

10 m

Shi

eld

Sig

nalS

upply

Circu

it Ch

eck

120%

80% 80%

CoverageHalf-Circle

100% 100%

100%

Range is 2

to 2

.5 m

ete

rs

360°360°

Point Sensor

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Fiber-Optic Sensors

One fiber-optic sensor can replace several point sensors

� 8-m flexible fiber

� 360°detection angle

� LED for visual feedback

� Built-in circuit check

� Electrically extendable

� Plug-in connector

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Multi-Unit Installation Example

Electrical cablesSensors Detecting ArcFiber-Optic SensorPoint Sensors

Trip

L1 L2 L3

LINK

SwitchboardSupply

2

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100-230 V

Log with Date and Time

• Event log with date and time• Performance graphs• Waveform capture

USB

Logging & Diagnostics

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Learn:

� Reasons for Reducing Risk of Arc-Flash Hazards

� OSHA’s position on Arc Flash Hazards

� How to use Hierarchies to prioritize Design Techniques and Products that can lower hazards and increase safety

– Current-Limiting fuses

– High-Resistance Grounding Systems

– Arc-Flash Relays

– Arc-Resistant safety products

Goals of Presentation

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Arc Resistant Controllers and Switchgear

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Other safety equipment in design

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Example of a Risk Assessment Matrix

Source: ANSI/AIHA Z10-2005: A new benchmark for safety management systems, Fred A.

Manuele, Safety Management, Feb 2006

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Align Hierarchy with Design Techniques and Products that increase Safety

1. Elimination – Design to eliminate hazards

2. Substitution – Substitute or reduce the hazard

3. Engineering – Equipment modifications, etc

4. Administration – Procedures, Training, etc

5. Personal Protective Equipment – Safety glasses, face shields, gloves, etc

1. Do not work on live equipment

2. Reduce Hazard:

1. Current-limiting fuses

2. Resistance-Grounding

3. Arc-Flash Relay

3. Safety Products

4. Implement and maintain safe working practices

5. Always use Personal Protective Equipment

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Q & A

Electrical Safety

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Thank you for attending!For more information, please contact:

Tony Locker, P.E.

Littelfuse513-693-5956

tlocker@littelfuse.com