Plan
every job. Decide on your approach and step-by-step procedures.
Write down first-time procedures. Discuss hazards and procedures
in a job briefing with your supervisor and other workers before
starting a job. Your employer should already have or develop a
permit system for working on live circuits, if a circuit must
be worked live.
- Identify the hazards. Do a job hazard analysis
(see fig. 1). Identify steps that could create electric shock
or arc-flash hazards.
- Minimize the hazards. De-energize the equipment
or insulate or isolate exposed live parts so you cannot contact
them. If this is impossible, get proper personal protective
equipment (PPE) and tools.
- Anticipate problems. If it can go wrong, it might.
Make sure you have the right PPE and tools for the worst-case
scenario.
- Get training. Make sure you and everyone working
with you is a qualified person with appropriate training for
the job.*
One of the
most important decisions in planning an electric task is whether
to de-energize. Whenever possible, live parts to which you might
be exposed should be put into an
electrically safe work condition,
unless your employer can demonstrate that de-energizing creates
more or worse hazards, or is not practical because of equipment
design or operational limitations.
You might need to work live to avoid interrupting life-support
systems, deactivating emergency alarm systems, or shutting down
ventilation equipment for hazardous locations, for instance. And
de-energizing would not be practical during testing of live electric
circuits or work on circuits that are part of a continuous process
that cannot be completely shut down.
An Electrically
Safe Work Condition
The most important principle of electric safety is, a
ssume
electric circuits are energized unless you make sure they are
not. Test
every circuit and conductor every time you
work on them. The National Fire Protection Association lists six
steps to ensure conditions for electrically safe work.**
- Identify all sources of power to the equipment.
- Interrupt the load current, then open the disconnecting
devices for each power source.
- Where possible, visually verify that blades of disconnecting
devices are fully open or that drawout-type circuit breakers
are fully withdrawn.
- Apply lockout/tagout devices in accordance with a formal,
written policy.
- Test each phase conductor or circuit part with an adequately
rated voltage detector to verify that the equipment is de-energized.
Check the voltage detector before and after each test to be
sure it is working.
- Properly ground all possible sources of induced voltage
and stored electric energy (such as, capacitors) before touching.
If conductors or circuit parts that are being de-energized
could contact other exposed conductors or circuit parts, apply
ground-connecting devices rated for the available fault current.
The process of de-energizing is "live" work and can result
in an arc flash due to equipment failure. When de-energizing,
follow the procedures described below in "Working On or Near Live
Circuits."
Lockout/tagout program
Your employer should establish a written lockout/tagout program
and train employees in the program. The program should cover planning
for locating and labeling energy sources, identifying employees
at risk, how and by whom the equipment is de-energized, releasing
of stored energy, verifying that the circuit is de-energized and
can't be restarted, voltage testing, grounding requirements, shift
changes, coordination with other jobs in progress, a procedure
for keeping track of all involved personnel, applying and removing
lockout/tagout devices, return to service, and temporary re-energizing
for testing/positioning. Lockout/tagout procedures should be developed
for each machine or piece of equipment that will require servicing.
Lockout/tagout application. Each person who could be exposed
to electric energy
must be involved in the lockout/tagout
process.
- After de-energizing, each employee at risk should apply
an individual lockout/tagout device to each source of electric
energy. Pushbuttons or selector switches cannot be used as
the only way to de-energize.
- A lockout device is a key or combination lock with a tag
that can be attached to a disconnecting device to prevent
the re-energizing of the equipment being worked on without
removal of the lock. The lockout device should have a way
of identifying whose lock it is. Individual lockout devices
with your name and picture on them are preferred. You must
be the only person who has the key or combination for
a lockout device you install, and you should be the only person
to remove the lock after all work has been completed.
- A tagout device is a tag and a way to attach it that can
withstand at least 50 pounds of force. Tagout devices should
be used alone only when it is not possible to install
a lockout device.
- The tag used in conjunction with a lockout or tagout device
must have a label prohibiting unauthorized operation of the
disconnecting means or unauthorized removal of the device.
- Before beginning work, you must verify through testing
that all energy sources have been de-energized.
- Electric lockout/tagout procedures should be coordinated
with all other site procedures for controlling exposure to
electric energy and other types of energy sources.
Individual qualified-employee control procedure. For minor
servicing, maintenance, inspection, and so on, on plug-connected
equipment, work may be done without attaching lockout/tagout devices
if the plug is next to where you are working and is always easy
to see, and you do not ever leave the equipment alone.
Complex lockout/tagout procedures. Special procedures are
needed when there is more than one energy source, crew, craft,
location, employer, way to disconnect, or lockout/tagout procedure
- or work that lasts beyond one shift. In any of these cases,
one qualified person should be in charge of the lockout/tagout
procedure with full responsibility for ensuring all energy sources
are under lockout/tagout and to account for all people on the
job. There should be a written plan addressing the specific details
and naming the person in charge.
Removal of lockout/tagout devices. Lockout and tagout devices
should be removed
only by the person installing them. If
work is not completed when the shift changes, workers arriving
on shift should apply their locks before departing workers remove
their locks.
Return to service. Once work is completed and lockout/tagout
devices removed, tests and visual inspection must confirm that
all tools, mechanical restraints, electric jumpers, shorts, and
grounds have been removed. Only then is it safe to re-energize
and return to service. Employees responsible for operating the
equipment and needed to safely re-energize it should be out of
the danger zone before equipment is re-energized.
Temporary release. If the job requiring lockout/tagout
is interrupted for testing or positioning equipment, follow the
same steps as in return to service (above).
Working on
live circuits means actually touching energized parts. Working
near live circuits means working close enough to energized parts
to pose a risk even though you make be working on de-energized
parts. Common tasks where you need to work on or near live circuits
include:
- Taking voltage measurements
- Opening and closing disconnects and breakers
- Racking breakers on and off the bus
- Removing panels and dead fronts
- Opening electric equipment doors for inspection.
There should be standard written procedures and training for these
common tasks. For instance, when opening and closing disconnects,
use the
left-hand rule when possible (stand to the right
side of the equipment and operate the disconnect with your left
hand). For other situations where you might need to work on or
near live circuits, your employer should institute a written live
work permit system which must be authorized by a qualified supervisor.
Live-work permit system
A live work permit should, at a minimum, contain this information:
- A description of the circuit and equipment to be worked
on and location
- The date and time covered by the permit
- Why live work will be done
- Results of shock hazard analysis and determination of shock
protection boundaries
- Results of flash hazard analysis and determination of flash
protection boundary
- PPE to be worn and description of safe work practices to
be used
- Who will do the work and how unqualified persons will be
kept away
- Evidence of completion of job briefing, including description
of job-specific hazards.
Approach distances to exposed live parts
The National Fire Protection Association defines three approach
distances for shock hazards and one for arc flash.***
Electric
shock (see table 1).
- The limited approach boundary is the closest distance
an unqualified person can approach, unless accompanied by
a qualified person.
- The restricted approach boundary is the closest
distance to exposed live parts a qualified person can approach
without proper PPE and tools. Inside this boundary, accidental
movement can put a part of your body or conductive tools in
contact with live parts or inside the prohibited approach
boundary. To cross the restricted approach boundary, the qualified
person must:
(a) Have a documented plan that is approved by the manager
responsible for the safety plan.
(b) Use PPE suitable for working near exposed live parts and
rated for the voltage and energy level involved.
(c) Be certain that no part of the body enters the prohibited
space.
(d) Minimize the risk from unintended movement, by keeping
as much of the body as possible out of the restricted space;
body parts in the restricted space should be protected.
The prohibited approach boundary is the minimum approach
distance to exposed live parts to prevent flashover or arcing.
Approaching any closer is comparable to making direct contact
with a live part. To cross the prohibited approach boundary,
the qualified person must:
(a) Have specified training to work on exposed live parts.
(b) Have a documented plan with proper written work procedures
and justifying the need to work that close.
(c) Do a written risk analysis.
(d) Have (b) and (c) approved by the manager responsible for
the safety plan.
(e) Use PPE appropriate for working near exposed live parts
and rated for the voltage and energy level involved.
Arc flash. The
flash protection boundary is the
distance at which PPE is needed to prevent incurable burns (2nd
degree or worse) if an arc flash occurs. (You still can get 1st
or 2nd degree burns.) For systems of 600 volts and less, the flash
protection boundary is 4 feet, based on an available bolted fault
current of 50 kA (kiloamps) and a clearing time of 6 cycles (0.1
seconds) for the circuit breaker to act, or any combination of
fault currents and clearing times not exceeding 300 kA cycles.
For other fault currents and clearing times,
see NFPA 70E.
Remember, when you have de-energized the parts you are going to
work on, but are still inside the flash protection boundary for
nearby live exposed parts: If the parts cannot be de-energized,
you must use barriers such as insulated blankets to protect against
accidental contact or you must wear proper PPE.
Proper Personal
Protective Equipment
When working on or around live circuits, be sure to wear the right
PPE to protect against electric shock and arc flash. Never wear
clothing made from synthetic materials, such as acetate, nylon,
polyester, or rayon - alone or combined with cotton. Such clothing
is dangerous because it can burn and melt into your skin.
The type of PPE worn depends on the type of electric work being
done (see table 2).
Once the hazard/risk category has been identified, check requirements
for clothing and other PPE when working on or near energized equipment
within the flash protection boundary (see tables 3 and 4). These
PPE requirements protect against electric shock and incurable
arc-flash burns. They do not protect against physical injuries
from arc blasts.
The minimum PPE required would be an untreated natural fiber long-sleeve
shirt and long pants with safety glasses with side shields (hazard/risk
category 0).
For more information, call your local union, CPWR – Center for Construction Research and Training (CPWR) (301-578-8500 or
www.cpwr.com),
the National Institute for Occupational Safety and Health (1-800-35-NIOSH
or
www.cdc.gov/niosh),
or OSHA (1-800-321-OSHA or
www.osha.gov)
Table 1. Approach boundaries to live parts for shock prevention
|
Limited
approach boundary |
|
Nominal
system voltage range, phase to phase |
Exposed
movable conductor |
Exposed
fixed- circuit part |
Restricted
approach boundary (allowing for accidental movement) |
Prohibited
approach boundary |
0
to 50 volts |
Not
specified |
Not
specified |
Not
specified |
Not
specified |
51
to 300 volts |
10
ft. 0 in. |
3
ft. 6 in. |
Avoid
contact |
Avoid
contact |
301
to 750 volts |
10
ft. 0 in. |
3
ft. 6 in. |
1
ft. 0 in. |
0
ft. 1 in. |
751
to 15,000 volts |
10
ft. 0 in. |
5
ft. 0 in. |
2
ft. 2 in. |
0
ft. 7 in. |
Source: From a portion of table 2-1.3.4, Approach Boundaries
to Live Parts for Shock Protection (NFPA 70E
Standard for Electrical
Safety Requirements for Employee Workplaces, 2000 edition).
Tables are reprinted with permission. Copyright ©2000 National
Fire Protection Association, Quincy, MA 02269. This reprinted
material is not the complete and official position of the National
Fire Protection Association on the referenced subject, which is
represented only by the standard in its entirety.
Table 2. Hazard risk category classification (within flash
protection boundary)
For
low-voltage tasks (600 volts and below), this table applies
only when there is an available short-circuit capacity of
25 kA or less, and when the fault clearing time is 0.03
seconds (2 cycles) or less. For 600-volt-class motor control
centers, a short-circuit current capacity of 65 kA or less
and fault-clearing time of 0.33 seconds (20 cycles) is allowed.
For 600-volt-class switchgear, you need a short-circuit
current capacity of 65 kA or less and fault-clearing time
of 1 second (60 cycles). For tasks not covered in this table
and tasks involving equipment with larger short-circuit
current capacities or longer fault-clearing times, a qualified
person must conduct a flash hazard analysis (see section
2-1.3.3, Part II, NFPA 70E). |
|
|
Hazard/risk
category |
Voltage-rated
Gloves Tools |
Opening
Doors and Covers |
Opening
hinged covers (to expose bare, energized parts) |
|
240
volts or less |
0
|
N
|
N
|
|
600-volt-class
motor control centers |
1
|
N
|
N
|
|
600-volt-class
lighting or small power transformers |
1
|
N
|
N
|
|
600-volt-class
switchgear (with power circuit breakers or fused switches) |
2
|
N
|
N
|
|
NEMA
E2 (fused contactor) motor starters, 2.3 kV through 7.2
kV |
3
|
N
|
N
|
|
1
kV and over (metal clad switchgear) |
3
|
N
|
N
|
|
1
kV and above metal clad load interrupter switches, fused
or unfused |
3
|
N
|
N
|
Removing
bolted covers (to expose bare, energized parts) |
|
240
volts or less |
1
|
N
|
N
|
|
600-volt-class
motor control centers or transformers |
2*
|
N
|
N
|
|
600-volt-class
lighting or small power transformers |
2*
|
N
|
N
|
|
600-volt-class
switchgear (with power circuit breakers or fused switches) |
3
|
N
|
N
|
|
NEMA
E2 (fused contactor) motor starters, 2.3 kV through 7.2
kV |
4
|
N
|
N
|
|
1
kV and above (metal clad switchgear) |
4
|
N
|
N
|
|
1
kV and above metal clad load interrupter switches, fused
or unfused |
4
|
N
|
N
|
Opening
transformer compartments for metal clad switchgear 1 kV
and above |
4
|
N
|
N
|
Installing,
Removing or Operating Circuit Breakers (CBs), Fused Switches,
Motor Starters or Fused Contactors |
Installing
or removing circuit breakers or fused switches, 240 volts
or less |
1
|
Y
|
Y
|
Inserting
or removing (racking) CBs from cubicles, doors closed
|
|
600-volt-class
switchgear (with power circuit breakers or fused switches)
|
2
|
N
|
N
|
|
NEMA
E2 (fused contactor) motor starters, 2.3 kV through 7.2
kV |
2
|
N
|
N
|
|
1
kV and above metal clad switchgear |
2
|
N
|
N
|
Inserting
or removing (racking) CBs or starters from cubicles, doors
open |
|
600-volt-class
switchgear (with power circuit breakers or fused switches)
|
3
|
N
|
N
|
|
NEMA
E2 (fused contactor) Motor Starters, 2.3 kV through 7.2
kV |
3
|
N
|
N
|
|
1
kV and above metal clad switchgear |
4
|
N
|
N
|
Operating
circuit breaker (CB), fused switch, motor starter or fused
contactor, covers on/doors closed |
|
240
volts or less |
0
|
N
|
N
|
|
>240-<600
volt panelboards/switchboards (molded case or insulated
case CBs) |
0
|
N
|
N
|
|
600
volt class motor control centers |
0
|
N
|
N
|
|
600
volt class switchgear (with power circuit breakers or fused
switches) |
0
|
N
|
N
|
|
NEMA
E2 (fused contactor) motor starters, 2.3 kV through 7.2
kV |
0
|
N
|
N
|
|
1
kV and above (metal clad switchgear) |
2
|
N
|
N
|
|
1
kV and above metal clad load interrupter switches, fused
or unfused |
2
|
N
|
N
|
Operating
circuit breaker, fused switch, motor starter or fused contactor,
covers off/doors open |
|
240
volts or less |
0
|
N
|
N
|
|
>240-<600
volt panelboards/switchboards (molded case or insulated
case CBs) |
1
|
N
|
N
|
|
600
volt class motor control centers |
1
|
N
|
N
|
|
600
volt class switchgear (with power circuit breakers or fused
switches) |
1
|
N
|
N
|
|
NEMA
E2 (fused contactor) motor starters, 2.3 kV through 7.2
kV |
2*
|
N
|
N
|
|
1
kV and above (metal clad switchgear) |
4
|
N
|
N
|
Working
on Energized Parts |
Working
on energized parts, voltage testing, applying safety grounds
|
|
240
volts or less |
1
|
Y
|
Y
|
|
>240-<600
volt panelboards/switchboards (molded case or insulated
case CBs) |
2*
|
Y
|
Y
|
|
600-volt-class
motor control centers |
2*
|
Y
|
Y
|
|
600-volt-class
switchgear (with power circuit breakers or fused switches) |
2*
|
Y
|
Y
|
|
600-volt-class
lighting or small power transformers |
2*
|
Y
|
Y
|
|
600-volt-class
revenue meters |
2*
|
Y
|
Y
|
|
NEMA
E2 (fused contactor) motor starters, 2.3 kV through 7.2
kV |
3
|
Y
|
Y
|
|
1
kV and above metal clad switchgear |
4
|
Y
|
Y
|
|
1
kV and above metal clad load interrupter switches, fused
or unfused |
4
|
Y
|
Y
|
Working
on control circuits with exposed energized parts, 120 volts
or below |
|
600-volt-class
motor control centers |
0
|
Y
|
Y
|
|
600-volt-class
switchgear (with power circuit breakers or fused switches |
0
|
Y
|
Y
|
|
NEMA
E2 (fused contactor) motor starters, 2.3 kV through 7.2
kV |
0
|
Y
|
Y
|
|
1
kV and above metal clad switchgear |
2
|
Y
|
Y
|
Working
on control circuits with exposed energized parts, over 120
volts |
|
600-volt-class
Motor Control Centers |
2*
|
Y
|
Y
|
|
600-volt-class
switchgear (with power circuit breakers or fused switches) |
2*
|
Y
|
Y
|
|
NEMA
E2 (fused contactor) motor starters, 2.3 kV through 7.2
kV |
3
|
Y
|
Y
|
|
1
kV and above metal clad switchgear |
4
|
Y
|
Y
|
Other
Tasks |
Reading
panel meters while operating meter switches |
0
|
N
|
N
|
Metal
clad load interrupter switches, fused or unfused, 1 kV and
above |
|
Outdoor
disconnect switch operation (hookstick operated) |
3
|
Y
|
Y
|
|
Outdoor
disconnect switch operation (gang-operated, from grade) |
2
|
N
|
N
|
|
Insulated
cable examination, in open area |
2
|
Y
|
N
|
|
Insulated
cable examination, in manhole or other confined space |
4
|
Y
|
N
|
Removing/installing
other equipment |
|
Starter
"buckets" for 600-volt-class motor control centers |
3
|
Y
|
N
|
|
600-volt-class
revenue meters |
2*
|
Y
|
N
|
|
Covers
or cable troughs for 600-volt-class revenue meters |
1
|
N
|
N
|
|
2*
= A double-layer switching hood and hearing protection are
required, in addition to the other hazard/risk category
2 requirements of table 3-3.9.2 of Part II of NFPA 70E.
See tables 3 and 4. |
|
kV
= kilovolt |
|
|
|
Note:
Applying safety grounds after voltage testing does not require
voltage-rated tools. Voltage-rated gloves or tools are rated
and tested for the maximum line-to-line voltage on which
work will be done. The hazard/risk category may be reduced
by one number for low-voltage equipment listed here where
the short-circuit current available is less than 15 kA (less
than 25 kA for 600-volt-class switchgear). |
|
Source:
Adapted from table 3-3.9.1, Hazard Risk Category Classifications
(NFPA 70E Standard for Electrical Safety Requirements
for Employee Workplaces, 2000 edition). Tables are reprinted
with permission. Copyright ©2000 National Fire Protection
Association, Quincy, MA 02269. This reprinted material is
not the complete and official position of the National Fire
Protection Association on the referenced subject, which
is represented only by the standard in its entirety. |
Table 3. Simplified, two-category, flame-resistant clothing system
Applicable
tasks |
Clothing
requirement |
All
hazard/risk category 1 and 2 tasks listed in table 2
On systems operating at less than 1000 volts, these tasks
include work on all equipment except
- Insertion/removal
of low-voltage motor starter "buckets"
-
Insertion/removal of power circuit breakers with the
switchgear doors open
-
Removal of bolted covers from switchgear.
On systems
operating at 1000 volts or more, tasks also include the
operation, insertion, or removal of switching devices with
equipment enclosure doors closed. |
Everyday
work clothing
Flame-resistant long-sleeve shirt (minimum ATPV of 5) worn
over an untreated cotton T-shirt with FR pants (minimum
ATPV of 8)
Or
FR coveralls (minimum ATPV of 5) worn over an untreated
cotton T-shirt (or an untreated natural-fiber long-sleeve
shirt) with untreated natural-fiber pants. |
All
hazard/risk category 3 and 4 tasks listed in table 2
On systems operating at 1000 volts or more, these tasks
include work on energized parts of all equipment. On systems
of less than 1000 volts, tasks include insertion or removal
of low-voltage motor-start motor control center "buckets,"
insertion or removal of power circuit breakers with the
switchgear enclosure doors open, and removal of bolted covers
from switchgear. |
Electric
"switching" clothing
Double-layer FR flash jacket and FR bib overalls worn
over either FR coveralls (minimum ATPV of 5) or FR long-sleeve
shirt and FR pants (minimum ATPV of 5) worn over
untreated natural-fiber long-sleeve shirt and pants worn
over an untreated cotton T-shirt
Or
Insulated FR coveralls (minimum ATPV of 25, independent
of other layers) worn over untreated natural-fiber
long-sleeve shirt with untreated cotton blue jeans ("regular
weight," minimum 12 oz./sq. yd. fabric weight), worn
over an untreated cotton T-shirt. |
FR - flame
resistant.
ATPV - arc thermal performance exposure value of the clothing
in calories/cm2.
Source: Based on Table F-1 in appendix F of NFPA 70E,
Electrical
Safety Requirements for Employee Workplaces, 2000.
Table 4. Flame-resistant protective clothing and equipment
Flame-resistant
protective clothing and equipment |
Protective
systems for hazard/risk category (4 = most hazardous) |
Hazard/risk
category number
Flash suit jacket (2-layer)
Flash suit pants (2-layer)
Head protection
Hardhat
Flame-resistant hardhat liner
Eye protection (safety glasses + side shields or safety
goggles)
Face protection (double-layer switching hood)
Hearing protection (ear canal inserts)
Leather gloves or voltage-rated gloves with leather protectors
Leather work shoes |
1
X
X
As
needed As needed
|
2
X
X
2*
tasks
2*tasks
X
X
|
3
X
X
X
X
X
X
X |
4
X
X
X
X
X
X
X
X
X
X |
Source:
Based on personal protective equipment requirements of table 3-3.9.2
of NFPA 70E,
Electrical Safety Requirements for Employee Workplaces.
Tables are reprinted with permission. Copyright ©2000 National
Fire Protection Association, Quincy, MA 02269. This reprinted
material is not the complete and official position of the National
Fire Protection Association on the referenced subject, which is
represented only by the standard in its entirety.
Figure 1. Hazard / risk analysis
flow
Source: Adapted from figure D-1 of NFPA 70E, Electrical
Safety Requirements for Employee Workplaces. Tables are reprinted
with permission. Copyright ©2000 National Fire Protection Association,
Quincy, MA 02269. This reprinted material is not the complete
and official position of the National Fire Protection Association
on the referenced subject, which is represented only by the standard
in its entirety.
* OSHA defines an electrical-qualified person as "one familiar with the construction and operation of the equipment and the hazards involved."
**Portions of text are reprinted with permission from NFPA 70E Electrical Safety Requirements for Employee Workplaces, section 2-1.1.3. Copyright ©2000 National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and official position of the National Fire Protection Association on the referenced subject, which is represented only by the standard in its entirety.
***Portions of text are reprinted with permission from NFPA 70E Electrical Safety Requirements for Employee Workplaces, definitions and Part II, Appendix A: Limits of approach. Copyright ©2000 National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and official position of the National Fire Protection Association on the referenced subject, which is represented only by the standard in its entirety.