Transcript Electrical in Construction

Office of Safety & Health Consultation
presents
Electrical in Construction
Objectives
In this course, we will discuss the
following:
• Common electrical hazards
• Standards relating to those hazards
• Electrical equipment defects/hazards
• Tools/techniques used in identifying
hazards
29 CFR 1926 - Subpart K
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1926.400 – Introduction
1926.402 – Applicability
1926.403 – General requirements
1926.404 – Wiring design and protection
1926.405 – Wiring methods, components, and equipment
1926.406 – Specific purpose equipment and installations
1926.407 – Hazardous (classified) locations
1926.408 – Special systems
1926.416, 417, 431, 432, 441 – Safety-related practices and
maintenance
• 1926.449 - Definitions
Common Electrical Hazards
• Electric shock/electrocution occurs, when
current flows through the body damaging the
body.
• Electrical burns are caused by arc blast or hot
conductors.
• Indirect falls from ladders, scaffolds or other
walking and working surfaces.
Common Electrical Hazards
• Explosions can be caused when electricity provides a
source of ignition for an explosive mixture in the
atmosphere.
• Fires are caused by overloading a circuit or appliance
or by current flowing through
high resistance due to faulty
wiring, setting fire to insulation
and surrounding materials.
General Requirements
1926.403(a)
General Requirements
• Electrical equipment must be free from
recognized hazards that can cause death or
serious physical harm to employees
– Suitability for installation
– Mechanical strength and
durability
– Electrical insulation
– Heating effects under
condition of use
– Arcing effects
– Classification by type, size, voltage,
1926.403(b)(1)
current capacity, specific use
General Requirements
• Listed, labeled, or
certified equipment
must be installed
and used in
accordance with
instructions included
in the listing,
labeling or
certification
1926.403(b)(2)
Nationally Recognized Testing Laboratories
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Canadian Standards Association (CSA International)
Communication Certification Laboratory, Inc. (CCL)
Curtis-Straus LLC (CSL)
FM Approvals LLC (FM)
Intertek Testing Services NA, Inc. (ITSNA)
MET Laboratories, Inc. (MET)
NSF International (NSF)
National Technical Systems, Inc. (NTS)
SGS U.S. Testing Company, Inc. (SGSUS)
Southwest Research Institute (SWRI)
TUV SUD America, Inc. (TUVAM)
TUV SUD Product Services GmbH (TUVPSG)
TUV Rheinland of North America, Inc. (TUV)
Underwriters laboratory Inc. (UL)
Wyle Laboratories, Inc. (WL)
Box Not Approved as a Pendant
General Requirements
• Equipment shall be installed and used in
accordance with instructions.
1926.403(b)(2)
Used in Accordance With Instructions
General Requirements
• Splices
– Splicing devices suitable for use
– Welding/brazing/soldering
– Mechanically/electrically secure
before soldering
– Covered with insulation equivalent
to that of the conductors
– Insulating device suitable for
purpose
1926.403(e)
General Requirements
• Each service, feeder,
and branch circuit, at
its disconnecting
means or over
current device, shall
be legibly marked to
indicate its purpose.
1926.403(h)
General Requirements
• Live parts of
electric equipment
operating at 50 volts
or more shall be
guarded against
accidental contact
by cabinets or other
forms of enclosures,
or by another
suitable method.
1926.403(i)
Wiring Design and Protection
• Polarity of
connections
– No grounded
conductor may be
attached to any
terminal or lead so as
to reverse designated
polarity
Correct Polarity
Hot
Neutral
Ground
Hot
Ground
Neutral
Reversed Polarity
1926.404(a)(2)
Wiring Design and Protection
• Employer shall use
either ground fault
circuit interrupters,
or
• An assured equipment
grounding conductor
program to protect
employees
1926.404(b)(1)(i)
Wiring Design and Protection
• Portable generators need not be grounded if:
– Supplies only equipment
mounted on the generator
and/or cord and plug
equipment is plugged into
receptacle mounted on the
generator
– Noncurrent-carrying metal
parts of equipment and
grounding conductor
terminals of the receptacle
are bonded to generator frame
1926.404(f)(3)
Wiring Design and Protection
• Vehicle-mounted generators; vehicle frame
may serve as system grounding if:
– The frame of the generator
is bonded to the vehicle
frame and ….
– Generator supplies only
equipment located on the
vehicle and/or equipment
plugged into the generator
and ….
1926.404(f)(3)
Wiring Design and Protection
– The noncurrent-carrying metal parts of
equipment and grounding conductor terminals of
the receptacles are bonded to the generator
frame, and ….
– The system complies with all other provisions of
this section.
1926.404(f)(3)
Wiring Design and Protection
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The path to ground from
circuits, equipment,
enclosures must be
permanent and
continuous.
1926.404(f)(6)
Wiring Design and Protection
• Equipment connected by cord and plug
– Noncurrent-carrying metal parts which may
become energized must be grounded
1926.404(f)(7)(iv)
Wiring Design and Protection
• Equipment connected by cord and plug must be
grounded, if:
– In a hazardous location
– Operated at over 150 V to
ground
• Except guarded motors and
appliances permanently insulated
from ground
– Hand held motor-operated tools
– Equipment used in wet and/or
conductive locations
– Portable hand lamps
1926.404(f)(7)(iv)
Wiring Design and Protection
• Flexible cords and cables must be protected
from damage.
1926.404(a)(2)(ii)(I)
Wiring Design and Protection
• Extension cord sets used with portable electric
tools and appliances must be of three-wire type
and must be designed for hard or extra-hard
usage.
1926.404(a)(2)(ii)(J)
Wiring Design and Protection
• Conductors entering boxes, cabinets, or
fittings must be protected from abrasion.
1926.404(b)(1)
American Wire Gauge
Note: The larger the gauge number, the smaller the wire.
Wire Rating
Wire Size:
Handles up to:
Allowable
ampacities:
#10 AWG
30 amps
28 amps
30 amps
#12 AWG
25 amps
23 amps
20 amps
#14 AWG
20 amps
17 amps
15 amps
#16 AWG
18 amps
8 amps
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Unless permitted
in NEC 240.4(E-G):
Safety factor of 20%
Tool
Estimated
Watts
Amperage Used
Receptacle
Amperage
25
40
Maximum
Amperage Load
(less 20%)
Jig Saw
300
2.5 (*5.0 motor startup)
Table Saw
1800
15
7 ¼” Circular Saw
1200
10
Chop Saw
1550
13
Total Usage
4850
43 (* includes startup)
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32
Wiring Design and Protection
1926.405(b)(1)
Wiring Design and Protection
• Unused openings in cabinets, boxes and
fittings must be effectively closed.
1926.405(b)(1)
Wiring Design and Protection
• All pull boxes, junction
boxes, and fittings must
be provided with a
cover.
• If metal covers are used,
they must be grounded.
1926.405(b)(2)
Wiring Design and Protection
• Flexible cords and
cables must be
suitable for
conditions of use and
location.
1926.405(g)(1)
Wiring Design and Protection
• Permitted uses of flexible cords and
cables
– Pendants
– Fixture wiring
– Portable lamps and
appliances
– Elevators cables, cranes,
and hoists
– Stationary equipment
– Frequent interchange
– Appliances – to permit removal
for maintenance and repair
1926.405(g)(1)
Wiring Design and Protection
• Prohibited uses of flexible cords and
cables
– As substitute for fixed wiring of structure
– Run through holes in walls, ceilings or
floors
– Run through doors, windows or similar
openings
– Attached to building surfaces
– Concealed behind building walls,
ceilings, or floors
1926.405(g)(1)(iii)
Flexible Cord Run Above Ceiling
Wiring Design and Protection
• Flexible cords shall be
connected to devices and
fittings so that strain
relief is provided.
– Will prevent pull from
being directly transmitted
to joints or terminal screws
1926.405(g)(2)(iv)
Wiring Design and Protection
Safety-Related Work Practices
• Employer must not permit an employee to
work in such proximity to any part of an
electric power circuit.
– If employee could
contact the power
circuit, it must be
de-energized or
guarded.
1926.416(a)(1)
Safety-Related Work Practices
• Working spaces, walkways, and similar
locations shall be kept clear of cords so as not
to create a hazard to employees.
1926.416(b)(2)
Safety-Related Work Practices
• Worn or frayed
electric cords must not
be used.
• Extension cords shall
not be stapled, hung
from nails or
suspended by wire.
1926.416(e)
Tools for Identifying Hazards
• An electrical receptacle
voltage tester with GFCI
tester.
– Line voltage probes
Summary
In this course, we discussed:
– Common electrical hazards
– Standards relating to those hazards
– Electrical equipment defects/hazards
– Tools/techniques used in identifying hazards
Recognize Any Hazard(s)?
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Yes
No employer shall permit a
worker to work in such
proximity to any part of an
electric power circuit that
the worker could contact the
electric power circuit in the
course of work
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Recognize Any Hazard(s)?
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Yes
Crossing electrical line
must be supported,
protected or removed to
safeguard workers
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Recognize Any Hazard(s)?
48
Yes
Spliced electrical
extension cords.
Extension cords
should be
marked DO NOT
USE. Also, bad
housekeeping,
trip hazard and
unprotected hole
in photograph
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Recognize Any Hazard(s)?
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YES
1. No GFCI
2. System not
grounded
3. Openings where
conductors entered
not closed
4. No cover on
boxes
5. Panel boards
were not dead front
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Recognize Any Hazard(s)?
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YES
Electric drill
flexible cord
was spliced to
a non-flexible
conductor with
damaged
insulation
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Recognize Any Hazard(s)?
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Yes
Scaffold was erected 4 ½
feet from 7.2 kV power
lines
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Recognize Any Hazard(s)?
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YES
Continuous
path to
ground not
maintained;
multiple
cords used
for fixed
equipment
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Recognize Any Hazard(s)?
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YES
Employer was
operating a
stand fan
without
grounding
protection
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Recognize Any Hazard(s)?
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Yes
Conductors entering boxes,
cabinets, or fittings shall be
protected from abrasion.
Openings through which
conductors enter shall be
effectively closed
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Recognize Any Hazard(s)?
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Yes
Flexible cords and
cables may pass
through doorways
or other pinch
points, if
protection is
provided to avoid
damage
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Your Questions?