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DOE Handbook
Electrical Safety
- Temporary Wiring -
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8.0 TEMPORARY WIRING
It is required that temporary wiring comply with all the requirements pertaining to permanent
wiring unless specific exceptions are stated, which can be found in NEC Article 527.
The following codes
and standards will aid in designing, installing, and inspecting temporary
wiring methods and using portable
electric hand tools.
1. Articles 230, 527, and 400 of the National Electrical Code (NEC 2002)
2.
Chapter 4 of NFPA 70E, Standard for Electrical Safety in the Workplace.
8.1 REQUIREMENTS AND INSTALLATION
CONDITIONS OF USE
Temporary electrical installations shall be allowed during periods of construction,
remodeling,
maintenance, repair, or demolition of equipment or structures or for experiments and
developmental work. However, such temporary installations are not substitutes for permanent
installations and
shall be removed as soon as the construction, remodeling, experiment, or other
special need is completed.
8.1.1 CONTACT PREVENTION
Except as modified in Article 527, temporary wiring shall meet all the
requirements of the NEC
for permanent wiring to prevent accidental contact by workers or equipment.
8.1.2 VERTICAL CLEARANCES
Vertical clearance of wires, conductors, and cables above ground shall meet the
requirements
of NEC.
8.1.3 WET LOCATIONS
Conductors with nonrated weather-proof insulation shall
not be enclosed in metal raceways or
used for wiring in tanks, penstocks, or tunnels. Receptacles used in damp
or wet locations shall
be approved for the purpose. When a receptacle is installed outdoors (outdoors is
considered a
wet location), it shall be contained in a weatherproof enclosure, the integrity of which would not
be affected when an attachment plug is inserted.
All temporary lighting strings in outdoor or wet
locations, such as tunnels, culverts, valve pits,
outlets, and floating plants, shall consist of lamp sockets
and connection plugs permanently
molded to the hard service cord insulation.
8.1.4 SUPPORTS
Bare or open conductors shall be insulated from their supports. This requirement prevents
arcing, sparking, or flash-over to grounded objects. Open wiring for temporary installations is
only allowed as per NEC Section 527.
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8.1.5 CONDUIT
Temporary wiring installed in conduit shall have bushings at all outlets and terminals
to prevent
abrasion and damage to the insulation.
8.1.6 LIGHTING
All lamps for general illumination should be protected from accidental contact or breakage.
Metal-case sockets
shall be grounded.
Temporary lights shall not be suspended by their electric cords unless cords and lights
are
designed for this means of suspension. Temporary lighting used in damp, wet, or hazardous
areas shall be
marked as suitable for use in those locations.
Portable electric lighting used in wet or other conductive locations (for example, drums, tanks,
and vessels) shall be operated at 12V or less. However, 120-V lights may be used if protected
by a GFCI.
Receptacles on construction sites shall not be installed on branch circuits that supply
temporary
lighting.
8.1.7 CONFINED SPACES
When temporary wiring is used in tanks or other
confined spaces, an approved disconnecting
means (identified and marked) shall be provided at or near the
entrance to such spaces for
cutting off the power supply in emergencies.
Portable electric lighting used in confined wet or hazardous locations such as drums, tanks,
vessels, and grease pits shall be operated at a maximum of 12 V, be intrinsically safe, or be
protected by a GFCI circuit.
8.1.8 EXPOSED SOCKETS AND BROKEN BULBS
Exposed empty light sockets and
broken bulbs shall not be permitted. This rule is to protect
personnel from accidentally contacting the live
parts in the socket and being shocked.
8.1.9 GROUND FAULT PROTECTION FOR PERSONNEL
Temporary power
to equipment used by personnel shall be protected by GFCI devices, where
required, or included in an assured
equipment grounding conductor program, where
permissible. See NEC 527 and NFPA 70E Chapter 4 for further
information.
8.1.10 WIRING METHODS
The requirements for temporary wiring for power and lighting
purposes include provisions for
wire connections, junction boxes, and overcurrent protection, as well as the
use of conductors.
See NEC 527.
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8.1.10.1 SERVICE CONDUCTORS
Service conductors shall comply with all the provisions of Article 230 in the
NEC when they are
used as wiring methods to supply temporary power systems.
8.1.10.2 FEEDER CONDUCTORS
Feeders are the conductors that transmit power from the service equipment to
the distribution
panelboard or between the main disconnect and the branch circuit over current devices (circuit
breakers, fuses). Feeders for temporary wiring shall originate inside an approved distribution
center, such as
a panel board, that is rated for the voltages and currents the system is expected
to carry. Some equipment is
manufactured specifically for temporary use.
Feeders can be run as cable assemblies, multiconductor cords,
or cables with two or more
conductors each with their own insulations, run together in the same cord or cable.
8.1.10.3 BRANCH CIRCUIT CONDUCTORS
Branch circuits are the conductors between the last overcurrent device
in an electrical system
and the outlets, such as receptacles, lighting outlets, and outlets for electrical
equipment wired
directly into a circuit. Branch circuits for temporary wiring shall originate inside an
approved
panelboard or power outlet that is rated for the voltages and currents the system is expected to
carry. As with feeders, branch circuit conductors can be contained within multiconductor cord or
cable
assemblies.
8.1.10.4 NONMETALLIC SHEATHED CABLE
Nonmetallic sheathed cable shall be used as allowed
by the NEC and as follows:
1. Along studs, joists, or similar supports closely following the building finish or running boards
when 7
feet 8 inches or more above the floor
2. When firmly attached to each cabinet, box, fitting, or fixture by
means of a cable clamp.
Nonmetallic sheathed cable shall not be used where precluded by the NEC as follows:
1. As portable extension cords
2. Lying on the ground subject to any type of traffic
3. Where
subject to frequent flexing
4. As service entrance cable.
8.2 USING ASSURED EQUIPMENT GROUNDING
CONDUCTOR PROGRAM
Where GFCI devices are not used (See Section 2.7), the employer shall establish and
implement an assured
equipment grounding conductor program on construction sites covering
all cord sets, receptacles that are not a
part of the building or structure, and equipment
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connected by cord and plug that are available for use or used by employees. This program shall
comply
with the following minimum requirements:
1. A written description of the program, including the specific
procedures adopted by the
employer, shall be available at the job site for inspection.
2. The employer
shall designate one or more competent persons to implement the program.
3. Each cord set, attachment cap,
plug and receptacle of cord sets, and any equipment
connected by cord and plug, except cord sets and
receptacles that are fixed and not
exposed to damage, shall be visually inspected before each day's use for
external defects
such as deformed or missing pins or insulation damage and for indications of possible
internal damage.
Equipment found damaged or defective shall not be used until repaired.
4. The following tests shall be
performed on all cord sets, receptacles that are not a part of the
permanent wiring of the building or
structure, and cord-and-plug connected equipment
required to be grounded:
a. All equipment grounding conductors shall be tested for continuity and shall be electrically
continuous.
b. Each receptacle and attachment plug shall be tested for correct attachment of the
equipment
grounding conductor. The equipment grounding conductor shall be
connected to its proper terminal.
5. All
required tests shall be performed:
a. Before first use
b. Before equipment is returned to service following any repairs
c. Where there is evidence of damage.
d. At
intervals not to exceed 3 months, except that cord sets and receptacles which are
fixed and not exposed to damage shall be tested at intervals not exceeding 6 months.
6. The employer shall
not make available or permit the use by employees of any equipment
that has not met the requirements of this
section.
7. Tests performed as required in this section shall be recorded. This test shall identify each
receptacle, cord set, and cord-and-plug-connected equipment that passed the test and shall
indicate the last
date it was tested or the interval for which it was tested. This record shall be
kept by means of logs, color
coding, or other effective means and shall be maintained until
replaced by a more current record. The record
shall be made available on the job site
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Figure 8-1 An assured equipment grounding program may be used if approved by authority having jurisdiction.
8.3 PORTABLE ELECTRICAL TOOLS AND EQUIPMENT
The EPM program should include the essential ingredients of
Chapter 19 of NFPA 70B,
Portable Electrical Tools and Equipment, and ANSI/UL 45, Portable Electric Tools. This
includes
employee training, maintenance, cord and attachment plug care, extension cords, major
overhauls,
and leakage current testing.
8.3.1 INSPECTION AND MAINTENANCE
Portable electric tools and equipment
such as cords, plugs, and GFCIs should be inspected
before use by both the issuer and the user for signs of
chaffing, cracking, wear, or other forms
of faulty insulation; evidence of a faulty grounding conductor,
cracked plug, or receptacle
housing; bent or missing plug or connector prongs; dead front plugs, receptacle, or
connectors;
a missing, bent, or otherwise abused switch; or an improperly functioning trigger lock (deadman's
switch). While in use, tools and equipment should be observed for proper operation,
including any signs of overheating or excessive sparking. Portable electric tools, equipment, and
GFCIs should be inspected or trip tested by the user each day before use. Signs of a defect
shall require the
return of the device for repair.
Figure 8-1 An assured equipment grounding program may be used
if
approved by authority having jurisdiction.
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8.3.2 CONDITIONS OF USE
Portable electric tools, equipment, and GFCIs shall not be used in
hazardous locations unless
marked to indicate suitability for such use.
Portable electric tools and equipment shall not be handled or suspended by their cords. Tools
and equipment shall be used only for their intended purpose, and when guards are required,
such guards shall be
in place and functional.
Tools and equipment shall be grounded via the case, double-insulated, specially
approved low
voltage types, or self-contained, battery-operated.
Tools and equipment used in damp areas should be approved for such use. Generally, electrical
tools are not approved for use in wet or damp areas without other means of protection.
8.3.3 USE OF
EXTENSION CORDS
Use of extension cords should be minimized. Such cords shall be suitable for the intended
use,
such as waterproof connectors for wet or damp areas, and are subject to the same conditions
as the tool
or equipment cord. Generally, daisy chaining of extension cord sets is prohibited
unless specifically allowed
by the manufacturer and listed for this application.
Extension cords should be visually inspected before each use.
Extension cord sets used on construction
sites and used with portable metal electric tools and
appliances shall be of three-wire type and shall be
designed for hard or extra-hard usage.
Flexible cords used with temporary and portable lights shall be
designed for hard or extra-hard
use. OSHA recognizes hard-service cord (types S, ST, SO, and STO) and
junior-hard service
cord (types SJ, SJO, SJT, and SJTO) as suitable for extra-hard and hard use.
Note:
Extension cords approved for outdoor use may be identified by "outdoor" or "W-A" on the
jacket.
Flexible
cord sets shall be listed as an assembly by a national recognized testing laboratory
(See Section 2.5).
Flexible cord sets used on construction sites shall contain the number of
conductors required for the circuit
plus an equipment grounding conductor. The cords shall be
hard use or extra-hard use as specified in the NEC.
8.3.4 DOUBLE INSULATED TOOLS
The NEC references the use of double-insulated tools in UL Standard UL 1097,
Double
Insulation Systems for Use in Electrical Equipment, which provides the requirements for
equipment
marked "Double Insulation" or "Double Insulated." Since the end product standard
takes precedence, the
end-product UL Standard should also be consulted when there are
questions pertaining to products that require
double insulation.
Double insulation is a system comprised of two insulation systems (basic and
supplementary)
that are physically separated and are not subjected to temperature, contaminants and other
deteriorating factors at the same time.
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Basic insulation is applied to live parts to provide protection against electrical shock.
Supplementary insulation is independent of the basic insulation and provides protection against
electrical shock in case of failure of the basic insulation. Also of importance is the reinforced
insulation which consists of one or more layers of insulating material that, in itself, provides the
same
degree of protection as double insulation.
For example, two layers of insulation separating an armature
lamination from an armature
conductor is not double insulation. This is reinforced insulation. To achieve a
double insulated
system, one layer of insulation separates the armature lamination from the armature conductor
(basic insulation) and an insulating sleeve provides a second layer between the armature
lamination and the
motor shaft (supplementary insulation).
Generally, double insulated equipment is constructed so that double insulation is provided
between all live parts and (1) the accessible surfaces of the equipment, and (2) all inaccessible
parts and surfaces that are conductively connected to the accessible surfaces of the equipment.
Under certain conditions, reinforced insulation systems are acceptable when applied to
brushcaps; brushholders;
commutator, and end turns of armature winding switches; power
supply cords; and internal wiring.
Power
supply cords for double-insulated tools shall be jacketed and shall not include a
grounding conductor.
"Double insulated" or "double insulation" must be permanently marked on the tool. In addition
the double
insulated symbol (a square within a square) may be used.
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