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DOE Handbook |
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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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8-6 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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