2
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
3
Learn:
� Reasons for Reducing Risk of Arc-Flash Hazards
Goals of Presentation
4
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
5
� 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
6
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
7
Learn:
� Reasons for Reducing Risk of Arc-Flash Hazards
� OSHA’s position on Arc-Flash Hazards
Goals of Presentation
8
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
9
� 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.
10
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
11
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
12
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
13
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.
14
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
15
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.)
16
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
17
Effect of Upgrading Fuses
Class RK5
Class RK1
18
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
19
Initiators of Electrical Faults
� IEEE Std 493-1997 (Gold Book) Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems
20
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 !
21
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.
22
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
23
277VLG
277VLG
277VLG
~0VNG
Normal Operation – Low Voltage Resistance Grounding
24
480VLG
480VLG
0VLG
277VNG
2 ways to Detect Ground Fault on RG System –Voltage and Current
25
Resistor
Failure
Loose
Connection
Corrosion
Broken or
Grounded Wire
Stolen Wire(s)
Why monitor the resistor?
26
L
oad
Ground-Fault Relay
Failed Resistor - Impact on System
27
L
oad
Ground-Fault Relay
Failed Resistor – Impact on System
28
Failed Resistor – Impact on System
No Indication of a Ground Fault
29
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
30
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
31
� 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
32
Lifespan of an Arc Fault
1.1.
2.2.
3.3.
4.4.
5.5.
6.6.
33
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
34
Examples of Arc Faults
35
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
36
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
37
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
38
Multi-Unit Installation Example
Electrical cablesSensors Detecting ArcFiber-Optic SensorPoint Sensors
Trip
L1 L2 L3
LINK
SwitchboardSupply
2
39
100-230 V
Log with Date and Time
• Event log with date and time• Performance graphs• Waveform capture
USB
Logging & Diagnostics
40
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
41
Arc Resistant Controllers and Switchgear
42
Other safety equipment in design
43
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
44
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
45
Q & A
Electrical Safety
46
Thank you for attending!For more information, please contact:
Tony Locker, P.E.
Littelfuse513-693-5956