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Subpart S
Electrical
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Subpart S
Electrical Standards
1910.301
Introduction



(a) Design Safety Standards for Electrical Systems
– 1910.302-308
– 1910.309-330 (future design)
Safety-Related Work Practices
– 1910.331-360
(c) Safety-Related Maintenance Requirements
1910.361-380
Safety Requirements for Special Equipment
– 1910.381-399
(e) Definitions - 1910.399
–


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1910.302 - Electric
Utilization Systems
(a)





Scope
–(1) Coverage
–Equipment installations used within or on buildings,
structures, and other premises, including:
Yards
 Industrial substations
Carnivals
 Conductors connecting
supply of electricity
Parking/Other lots
 Other outside conductors
Mobile homes
on premises
Recreational vehicles
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1910.302 - Electric
Utilization System (Cont)
(a)(2) Not Covered:
Ship installations
 Watercraft
 Railroad rolling stock
 Aircraft
 Automotive vehicles
other than RV’s

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Railroad generating,
transforming,
transmitting or
distribution of power
 Communication
equipment
 Electric utilities

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1910.302 - Electric
Utilization Systems (Cont)
(b) Extent of application
(1) Requirements apply to all electrical installations
(regardless of when designed and installed) in sections:
— 1910.303(b)-(f)
— 1910.304(f)(3)-(4)
— 1910.303(g)(2)
— 1910.304(f)(5)(iv)(a)-(d)
— 1910.304(e)(1)(i)
— 1910.304(f)(5)(v)-(vi)
— 1910.304(e)(1)(iv)-(v)
— 1910.304(f)(6)(i)
— 1910.304(f)(1)(ii)-(v)
— 1910.305(g)(1)(i)-(iii)
— 1910.305(g)(2)(ii)-(iii)
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1910.302 - Electric
Utilization Systems (Cont)

(b)(2) Every system/equipment installed
after March 15, 1972, and major
replacements, modifications, repairs, or
rehabilitation after March 15, 1972 of older
systems, shall comply with 1910.302-308.
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1910.303
General Requirements


(a) Only approved conductors and equipment
(b) Examination, installation and use of equipment
– (1) Electrical equipment free from recognized
hazards likely to cause death/serious physical
harm to employees [5(a)(1)]
– (2) Installation and use - listed or labeled
equipment shall be used or installed in
accordance with any instructions included in
the listing or labeling
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1910.303 - General
Requirements (Cont)

(c) Splicing
– Conductors joined or spliced by
Brazing
» Welding
» Soldering
»
Covered by insulation
 (d) Arcing parts shall be enclosed
–
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1910.303 - General
Requirements (Cont)

(e) Marking - Electrical equipment shall be
marked:
–
–
–
–
–
–
Manufacture’s name
Trademark
Voltage
Current
Wattage
Durable markings
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1910.303 - General
Requirements (Cont)

(f) Identification of disconnecting means
and circuits for the following shall be
legibly marked and durable:
–
–
–
–
–
Motors
Appliances
Each service
Each feeder
Each branch circuit
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1910.303 - General
Requirements (

(g) 600V or less
– (1)(i) Working space about electrical equipment (Table S-1)
– (ii) Clear spaces: working space/no storage
– (2) Guarding of live parts
» 50V or more guarded against accidental contact by:
• Approved cabinets/enclosures
• Location in room/vault
• Partitions/screens (only qualified persons)
• Location on balcony, gallery, platform
• Elevation: 8 ft. or more above floor
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1910.303 - General
Requirements (Cont)

(h) Over 600V
– (3) Workspace about equipment
» See Table S-2
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1910.304 - Wiring Design
and Protection

(a) Use/identification of grounded/grounding
conductors
– (1) Distinguishable from other conductors (Usually
green)
– (2) Polarity of connections
» No reverse polarity on leads/terminals
– (b) Branch circuits
» (1) Reserved
» (2) Outlet devices
• Ampere rating not < load served
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1910.304 - Wiring Design
and Protection (Cont)

(c) Outside conductors - 600V or <
– (1) Conductors on poles - horizontal climbing space not less than:
» (i) Power conductors below communication conductors - 30”
» (ii) Power conductors alone or above communication conductors  300V or less - 24”
 > 300V - 30”
» (iii) Communication conductors below power conductors
* 300V or less - 24”
* 300V or more - 30”
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1910.304 - Wiring Design
and Protection (Cont)


(c)(2) Minimum clearances from ground:
– (i) 10 ft. - above finished grade, sidewalks, platforms
– (ii) 12 ft. - over areas subject to vehicle traffic (not truck traffic)
– (iii) 15 ft. - over areas subject to truck traffic
– (iv) 18 ft. - over public streets, alleys, roads, driveways
(3) Clearance from building openings - conductors shall have clearance of at
least 3 ft. from windows, porches, doors, and fire escapes
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1910.304 - Wiring Design
and Protection (Cont)

(c)(4) Clearance over roofs
– Conductors shall have clearance of at least 8 ft. from highest point of roofs
over which they pass
– Exceptions:
– (i) Voltage between conductors
» 300V or < and roof slope 4” in 12--clearance from roofs 3 ft.; or,
– (ii) Voltage between conductors
» 300V or < and conductors do not pass over more than 4 ft. of overhang
portion of roof--clearance from roofs 18”
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1910.304 - Wiring Design
and Protection (Cont)

(d) Services
– (1) Disconnecting means
» (i) General
 Shall be provided to disconnect conductors (in buildings
or structures) from service entrance conductors
 Indicators for open and closed positions
 Readily accessible location nearest point of entrance of the
service-entrance conductors
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1910.304 - Wiring Design
and Protection (Cont’d)

(d)(2) Services > 600V
– (i) Guarding -- Service entrance conductors installed as
open wires accessible only to qualified persons
– (ii) Warning signs -- High voltage signs for other than
qualified employees
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1910.304 - Wiring Design
and Protection (Cont)

(e) Overcurrent protection
– (1) Circuits 600V or <
» (i) Protection of conductors and equipment from overcurrent
» (ii) Grounded conductors
* Except for motor running overload protection, no interruption of
grounded conductors, unless all circuit conductors opened
simultaneously
* (iii) Disconnection of fuses and thermal cutouts
* Except service fuses, all fuses, thermal cutouts, circuits > 150V to
ground
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1910.304 - Wiring
and Protection (Cont)



(e)(1)(iv) Location in or on premises
– Overcurrent devices readily building management
personnel
(v) Arcing/Suddenly moving parts
– Fuses/circuit breakers located or shielded so not to
cause burns or injuries
(vi) Circuit breakers shall indicate
– Open (Off)
– Closed (On)
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1910.304 - Wiring Design
and Protection (Cont)

(f) Grounding
– (1) Systems to be grounded
» (i) All 3 wire DC systems - neutral conductor
grounded
» (ii) 2 wire DC systems over 50V to 300V
between conductors - grounded
– (2) Conductors to be grounded
» AC systems - identified
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1910.304 - Wiring Design
and Protection (Cont)


(f)(3) Grounding connections
(4) Grounding path
– Path to ground from circuits, equipment,
enclosures - permanent and continuous
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1910.304 - Wiring Design
and Protection (Con)

(f)(5) Supports, enclosures and equipment to be grounded
– (i) Metal cable trays, metal raceways, metal conductor
enclosures shall be grounded
– (v) Equipment connected by cord and plug
» Non-current carrying metal parts of cord and plug
connected equipment which may be energized shall be
grounded IF:
 in hazardous locations
 operated at > 150V
 of types such as: refrigerators, A.C., hand-held motor tools,
tools used in wet locations, portable hand lamps
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1910.305 - Wiring Methods,
Components and Equipment

(a) Wiring methods
– (1) General requirements
» (i) Metal raceways, cable armor, and other
metal enclosures shall be metallically joined
together into continuous electric conductor
and be connected to all boxes, fittings,
cabinets for effective electrical continuity
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1910.305 - Wiring
Methods, etc. (Cont)

(a)(2) Temporary wiring
– (i) Uses permitted - 600V or <
» (A) Remodeling, maintenance, repair,
demolition
» (B) Experimental or development work
» (C) Period not > 90 days for Christmas
lighting, etc.
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1910.305 - Wiring
Methods, etc. (Cont)


(b)(1) Conductors entering cabinets, boxes,
fittings
– Protected from abrasion
– Openings effectively closed
(2) Covers and canopies
– Pull boxes, junction boxes, fittings provided
with approved covers
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1910.305 - Wiring
Methods, etc. (Cont)

(c) Switches
–
–
(1) Knife - Single-throw type
» Blades dead - switch open position
» Placed so gravity will not tend to close switch
(2) Faceplates for flush-mounted snap switches
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1910.305 - Wiring
Methods, etc. (Cont)

(d) Switchboards and panel boards
–
–
–
Live parts located in dry locations
Accessible to qualified persons
Panel boards shall be mounted in cabinets,
cutout boxes or enclosures and dead front
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1910.305 - Wiring
Methods, etc. (Cont)


(e) Enclosures for damp or wet locations
– (1) Cabinets, cutout boxes, fittings, boxes, panel board
enclosures installed to prevent moisture in enclosures
– Wet locations - weatherproof enclosures
– (2) Weatherproof enclosures for
» Switches, circuit breakers, switchboards in wet locations
(f) Conductors for general wiring shall be:
– Insulated
– Approved for voltage, operating temperature, location of use
– Distinguishable by appropriate color or other suitable means
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1910.305 - Wiring
Methods, etc. (Cont)

(g) Flexible cords and cables
– (1) Approved usage
» Pendants
» Wiring of fixtures
» Connection of portable lamps and appliances
» Elevator cables
» Wiring of cranes and hoists
» Connection of stationary equipment to facilitate
interchange
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1910.305 - Wiring
Methods, etc. (Cont)

(g)(1)(iii) Flexible cords may not be used
– As a substitute for fixed wiring
– Where run through holes in walls, ceilings, floors
– Where run through doorways, windows, openings
– Attached to building surfaces
– Concealed behind walls, ceilings, floors
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1910.305 - Wiring
Methods, etc. (Cont)

(g)(2) Identification, splices and terminations
– (i) Conductors - Flexible cords and cables used as
grounded conductor or equipment grounding conductor
shall be distinguishable.
– Types SJ, SJO, SJT, SJTO, S, SO, ST, and STO shall be
durable marked with:
» Type designation
» Size
» Number of conductors
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1910.305 - Wiring
Methods, etc. (Cont)



(g)(2)(ii) Flexible cords
– Used only in continuous lengths (no splicing/taping)
– Hard surface #12 or larger may be repaired, if splicing retains
insulation and sheath properties
(iii) Flexible cords - connected to devices and fittings to provide
strain relief
(j) Equipment for general use
– (1)(i) Lighting fixtures, lampholders, lamps, receptacles and
rosettes
» No live parts exposed unless 8 ft. above
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1910.306 - Specific Purpose
Equipment and Installations

(a) Electric signs and outline lighting
– (1) Disconnecting means
(electronic/electromechanical controllers) » Capable of being locked in open position
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1910.306 - Specific Purpose
Equipment (Cont)

(b) Cranes/Hoists
– (1) Disconnecting means
» Between runway contact conductors and power supply
» Another means, capable of being locked in open position,
shall be provided
– (2) Control
» Limit switch to prevent load block passing safe upper limit
– (3) Clearance for working space/access to live parts - 2 ft. 6 in.
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1910.306 - Specific Purpose
Equipment (Cont)

(c) Elevators, dumbwaiters, escalators, moving walks
– (1) Disconnecting means - Have single disconnecting
means (ungrounded main power conductors)
– (2) Warning signs
– (3) Control panels
» Cabinets with doors
» Capable of being locked closed
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1910.306 - Specific Purpose
Equipment (Cont)

(d) Electric welders/disconnection means
– (1) In supply circuit for
» Each motor - generated arc welder
Not equipped
» Each AC transformer
with disconnect
» Each DC rectifier arc welder
in welder
– (2) Switch/circuit breaker provided so resistance
welders and control equipment isolated from supply
circuit
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1910.306 - Specific Purpose
Equipment (Cont)

(e) Data processing equipment
– Disconnecting means to all
» Electronic equipment in data
processing and computer rooms
» Air conditioning system
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1910.306 - Specific Purpose
Equipment (Cont)

(f) X-ray equipment - other than medical/dental use
– (1) Disconnecting means
» (i) In supply circuit
» Readily accessible from X-ray control
» (ii) High voltage switch or equivalent
– (2) Control
» (i) Radiographic/fluoroscopic types
» Effectively enclosed/interlocks
» (ii) Diffraction and irradiation types
» Energy indication
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1910.306 - Specific Purpose
Equipment (Cont)

(g) Induction/dielectric heating equipment
– (1) Scope
» Industrial
» Scientific
– (2) Guarding/grounding
» (i) Enclosures
» (ii) Panel controls
» (iii) Access to internal equipment
» (iv) Warning labels - “Danger”
» (v) Work applicator shielding
» (vi) Disconnecting means
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1910.306 - Specific Purpose
Equipment (Cont)

(h) Electrolytic cells
– (1) Scope
– (2) Definitions
» Cell line - assembly of electrically interconnected electrolytic
cells supplied by DC power
» Cell line attachments/auxiliary equipment
» Cell line working zone
» Electrolytic cells
– (3) Application
– (4) Disconnecting means
– (5) Portable electric equipment
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1910.306 - Specific Purpose
Equipment (Cont)
(h)(6) Power supply circuits and receptacles
for portable electric equipment
 (7) Fixed/portable electric equipment
 (8) Auxiliary non-electric connections
 (9) Cranes/hoists

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1910.306 - Specific Purpose
Equipment (Cont)


(i) Electrically driven/controlled irrigation machines
– (1) Lighting protection
– (2) Disconnecting means
(j) Swimming pools, fountains, similar installations
– (1) Scope
– (2) Lighting and receptacles
– (3) Cord/plug connected equipment
– (4) Underwater equipment
– (5) Fountains
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Electrical Safety-Related Work
Practices Standard
29 CFR 1910, Subpart S
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1910.331 - Scope
Covers both qualified and unqualified persons
working on, near or with electrical
conductors and equipment.
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1910.331 - Scope
Contains requirements for:
 Working on or near electrical equipment
 Use of electrical protective equipment
 The safe use of electrical equipment
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1910.331 - Scope
Does not cover work by qualified persons on:
 Generation, transmission and distribution
installations
 Communication installations
 Installations in vehicles
 Railway installations
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1910.332 - Training
Required for employees who face
the risk of electrical shock
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1910.332 - Content of Training
 Electrical
safe work practices
 Other safe work practices necessary for
safety
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1910.332 - Content of Training
Qualified persons shall also be trained in:
Distinguishing exposed live parts
 Determining normal voltage of parts
 Clearance distances and voltages

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1910.332 - Type of Training
Classroom or on the job,
depth of training based on risk
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1910.333 - Selection and Use of
Work Practices
Safe work practices shall be used and be
consistent with the nature and extent of the
associated hazard.
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1910.333(a)(1) - Selection and
Use of Work Practices


Live parts to which an employee may be exposed
shall be de-energized before the employee works
on or near them, unless de-energizing introduces
additional or increased hazards or is infeasible due
to equipment design or operational limitations.
Live parts that operate at less than 50 volts to
ground need not be de-energized if there will be
no increased exposure to electrical burns or to
explosion due to electrical arcs.
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1910.333(a)(2) - Selection and
Use of Work Practices

If the exposed live parts are not deenergized, other safety-related work
practices shall be used to protect employees
who may be exposed to the electrical
hazards involved.
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1910.333(b) - Working On or
Near Exposed De-energized Parts

(2) While any employee is exposed to
contact with parts of fixed electric
equipment or circuits which have been
de-energized, the circuits energizing parts
shall be locked out or tagged out or both.
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1910.333(b) - Working On or
Near Exposed De-energized Parts



(2)(ii)(B) The circuits and equipment to be worked
on shall be disconnected from all electric energy
sources.
(2)(ii)(C) Stored electric energy which might
endanger personnel shall be released.
(2)(ii)(D) Stored non-electrical energy in devices
that could reenergize electric circuit parts shall be
blocked or relieved to the extent that the circuit
parts could not be accidentally energized by the
device.
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1910.333(c) - Working On or
Near Exposed Energized Parts


(2) Only qualified persons may work on electrical
circuit parts or equipment that have not been
de-energized
(3) If work is to be performed near overhead lines,
the lines shall be de-energized and grounded, or
other protective measures shall be provided before
work is started
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1910.333(c)(3)
Overhead Lines

(ii) When a qualified person is working in the vicinity of
overhead lines, the person may not approach or take any
conductive object without an approved insulating handle closer
to exposed energized parts than shown in Table S-5 unless:
– (A) The person is insulated form the energized part
– (B) The energized part is insulated both from all other objects
conductive objects
– (C) The person is insulated from all conductive objects
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1910.333(c)(3)(iii) - Vehicular and
Mechanical Equipment
(Near overhead power lines)
Must be kept at least 10 ft away
 In transit, must be kept at least 4 ft. away
 Employees may not contact equipment if
approach distances can be violated

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1910.333(c)(4) - Illumination

(i) Employee may not enter spaces
containing exposed energized parts, unless
illumination is provided that enables the
employees to perform the work safely.
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1910.333(c)(5) - Confined or
Enclosed Spaces

Employees working near exposed live parts
shall be provided with and use protective
shields, barriers or insulating materials in
order to prevent inadvertent contact with
live parts.
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1910.333(c)(6) - Conductive
Materials and Equipment
Conductive material must be used in safe
manner
 Safe work practices must be used when
working with long, conductive objects

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1910.333(c)(7) Portable Ladders

Portable ladders shall be of nonconductive
materials if they are used where the
employee or the ladder could contact
exposed energized parts.
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1910.333(c)(8)
Conductive Apparel

Conductive clothing and jewelry cannot be
worn if they can come into contact with live
parts
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1910.333(c)(9)
Housekeeping Duties

Adequate safety precautions and
nonconductive cleaning materials must be
used around live parts
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1910.333(c)(10)
Interlocks
Only a qualified person may temporarily
defeat an interlock while working on
equipment
 Equipment must be returned to its operating
condition

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1910.334(a) - Portable Electrical
Equipment
Cannot staple cord in place
 Cannot lift or lower by cord
 Check cord for defects
 Cords to have proper grounding
 Cords must be approved for location
 Safe work practices must be in place before
starting work

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1910.335 - Safeguards for
Personnel Protection
Employers must provide
 Employees must wear if exposed to hazards
 Must be maintained in a safe condition
 Non-conductive head protection must be
worn

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1910.335(a)(2) - General
Protective Equipment and Tools
(i) Appropriate insulated tools must be used
around live parts
 (ii) Protective shields and barriers must be
used around live parts if they can be
contacted

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1910.335(b) Alerting Techniques

Safety signs, tags, barricades and sometimes
attendants must be used to alert employees
of electrical hazards
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