Electrical Safety
Tony Locker, P.E.
Littelfuse
513-693-5956
tlocker@littelfuse.com 1
Goals of Presentation
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
2
Goals of Presentation
Learn:
Reasons for Reducing Risk of Arc-Flash Hazards
3
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 ArcFlash/Arc-Blast Incidents.
* Source: National Safety Council
4
Effects of Electrical Hazards on Workers
Severe burns
Vision damage or
blindness
Hearing loss
Broken bones or
internal organ damage
Whiplash
Brain injuries
Lacerations
Fatality
Photos courtesy of OSHA
5
Effects of Electrical Hazards on Business
Costly Damage…
Equipment replacement
and need for capital
Equipment repair costs
Downtime
Production Loss (scrap)
Image from IEEE Electrical Safety Workshop, Floyd, Doan, Barrios, Wellman
…and business
interruption.
Image from IEEE Electrical Safety Workshop, H. Landis Floyd, II
6
Goals of Presentation
Learn:
Reasons for Reducing Risk of Arc-Flash Hazards
OSHA’s position on Arc-Flash Hazards
7
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
consensus standards such as NFPA 70E70E2004 to identify safety measures that can be
used to comply with or supplement the
requirements of OSHA's standards for
preventing or protecting against arcarc-flash
hazards…”
hazards…”
Source:
http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTER
PRETATIONS&p_id=25557
8
NFPA 70E, Standard for Electrical Safety in
the Workplace:
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
9
NFPA is a registered trademark of the National
Fire Protection Association (NFPA), Quincy, MA.
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
10
Goals of Presentation
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
11
Hierarchy of Controls – OSHA and ANSI Z10
1. Elimination – Design to
eliminate hazards
1. Engineering Controls –
Seek to eliminate the hazards
at the source.
2. Substitution – Substitute or
reduce the hazard
2. Safety/Process Controls –
Can not eliminate hazard …
reduce the hazard and/or
worker exposure to
hazardous conditions.
3. Engineering – Equipment
modifications, etc
4. Administration – Procedures,
Training, etc
3. PPE Controls – Devices and
clothing worn by workers to
safeguard themselves against
the hazards
5. Personal Protective
Equipment – Safety glasses,
face shields, gloves, etc
12
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 hazardous
method 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.
13
Goals of Presentation
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
14
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.)
15
Current Limitation
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.
16
Effect of Upgrading Fuses
Class
RK5
Class
RK1
17
Goals of Presentation
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
18
Initiators of Electrical Faults
IEEE Std 493-1997 (Gold Book)
Recommended Practice for the Design of
Reliable Industrial and Commercial Power
Systems
19
Breakdown of Electrical Faults
Current-limiting
fuses reduce
hazards on
3-phase faults
HRG Systems
prevent all hazards
associated with
ground faults !
* Source: Industrial Power System Grounding Design Handbook
by J.R. Dunki-Jacobs, F.J. Shields and Conrad St. Pierre
20
Resistance Grounded Systems vs SolidlyGrounded 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.
21
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
Source
(Wye)
AØ
BØ
N
Disadvantages
HRG
– Workers must be trained on system
22
CØ
Normal Operation – Low Voltage Resistance
Grounding
277VLG
~0VNG
277VLG
277VLG
23
2 ways to Detect Ground Fault on RG System –
Voltage and Current
480VLG
277VNG
480VLG
0VLG
24
Why monitor the resistor?
Broken or
Grounded Wire
Loose
Connection
Resistor
Failure
Stolen Wire(s)
Corrosion
25
Failed Resistor - Impact on System
L
o
a
d
Ground-Fault
Relay
26
Failed Resistor – Impact on System
L
o
a
d
Ground-Fault
Relay
27
Failed Resistor – Impact on System
No Indication of a
Ground Fault
28
New approach to NGR Monitoring
Voltage at the
neutral is
monitored
A voltage clamp in the
sensing resistor eliminates
hazardous voltage levels
at the relay
N
R
NGR
G
CT is used to
monitor groundfault current
Continuously monitors
resistance using sensing
resistor in parallel with NGR
29
Goals of Presentation
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
30
Breakthroughs in Arc Flash Relay Technologies
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
31
Lifespan of an Arc Fault
1.
4.
2.
5.
3.
6.
32
0
100
Ste
el
Fir
e
Co
pp
er
Fir
e
Fir
e
Total breaking time
with PGR-8800
1 + (35…60) ms
Ca
ble
Arc Energy (I2t, kA2s)
Lifespan of an Arc Fault
200
400 t (ms)
50 kA bolted fault between 480 Vac and ground
33
Examples of Arc Faults
34
Typical Wiring Diagram of an Arc-Flash Relay
To next PGR-8800
Inputs
i bi
t
p
-
T ri
+
Outputs
Online Service Tripped
Re
se
t
12-48 Vdc
In h
100-240
Vac/Vdc
To next PGR-8800
Positive Bus
Negative Bus
Trip Voltage
24 - 600 VDC
24 - 440 VAC
Battery (24 VDC)
L1 L2 L3
GND
Trip
Coil
USB
5A CTs
PC with
Microsoft Windows®
Three-phase
Overcurrent
Protection
Config, log &
firmware upgrade
Up to 6 Point or Fiber Optic Sensors
with built-in circuit-check
35
Point Sensors
d
Sh
iel
k
Ch ec
ly
pp
Sig n a
l
it
Circu
Su
10 m
8 mm
Sensor
Lens
52 mm
Red LED for
Circuit-check
& Visual Diagnostics
32 mm
Coverage
Half-Circle
120%
Range is 2 to 2.5 meters
Ø3.5 mm
100%
360°
360°
Mounting
Holes
(front / back)
100%80%
36
Point Sensor
80%100%
Fiber-Optic Sensors
8-m flexible fiber
360°detection angle
LED for visual feedback
Built-in circuit check
Electrically extendable
Plug-in connector
One fiber-optic sensor can replace several point sensors
37
Multi-Unit Installation Example
LINK
Switchboard
Supply
2
L1 L2 L3
Trip
Electrical cables
Sensors Detecting Arc
Fiber-Optic Sensor
Point Sensors
38
Logging & Diagnostics
Log with Date and Time
• Event log with date and
time
• Performance graphs
• Waveform capture
100-230 V
USB
39
Goals of Presentation
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
40
Arc Resistant Controllers and Switchgear
41
Other safety equipment in design
42
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
43
Align Hierarchy with Design Techniques and
Products that increase Safety
1. Elimination – Design to
eliminate hazards
1. Do not work on live
equipment
2. Substitution – Substitute or
reduce the hazard
2. Reduce Hazard:
1. Current-limiting fuses
3. Engineering – Equipment
modifications, etc
2. Resistance-Grounding
3. Arc-Flash Relay
4. Administration – Procedures,
Training, etc
3. Safety Products
4. Implement and maintain safe
working practices
5. Personal Protective
Equipment – Safety glasses,
face shields, gloves, etc
5. Always use Personal
Protective Equipment
44
Electrical Safety
Q&A
45
Thank you for attending!
For more information, please contact:
Tony Locker, P.E.
Littelfuse
513-693-5956
tlocker@littelfuse.com46