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ABE288 Design Safety Standards for Electrical Systems: Special Systems -OSHA Standard 1910.308 1Carol J. Lehtola, Charles M. Brown, and William J. Becker2 1. This document is ABE288, one of a series of the Agricultural and Biological Engineering Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date December 2000. Reviewed February 2008. Visit the EDIS Web Site at http://edis.ifas.ufl.edu. 2. Carol J. Lehtola, assistant professor and Extension Agricultural Safety Specialist; Charles M. Brown, coordinator information/publication services; William J. Becker, professor emeritus; Agricultural and Biological Engineering Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville. The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, DeanThe Impact of Safety on Florida AgricultureFlorida agriculture, including forestry and fishing, made an annual economic impact of $53 billion in 1998. More than 81,000 people work on the 40,000 farms in the state, and more than 50,000 are employed in other activities related to agriculture. The state's agricultural enterprises range from large citrus, vegetable and cattle operations to small family-operated farms. From 1989 to 1998, there were approximately 240 deaths related to agriculture in Florida, according to data compiled by the Deep-South Agricultural Health and Safety Center. In addition, agriculture has one of the highest injury and death rates among U.S. industries. Safety in Florida agriculture is challenging because: the state's agricultural enterprises are diverse, safety knowledge among workers varies, manual labor is used extensively, the climate creates year-round heat stress. Therefore, it is vital to assist the public in learning about OSHA documents related to agriculture. More related information is available at the following Web sites: Florida AgSafe:
Design Safety Standards for Electrical Systems: Special Systems -OSHA Standard 1910.308 2Contents of OSHA Standard 1910.308 Section 1910.308(a) -Systems over 600 Volts, Nominal Section 1910.308(b) -Emergency Power Systems Section 1910.308(c) -Class 1, Class 2, and Class 3 Remote Control, Signaling, and Power-limited Circuits Section 1910.308(d) -Fire Protective Signaling Systems Section 1910.308(e) -Communications Systems NOTE: Some sections of OSHA standards are labeled "Reserved." This label implies either that information has been deleted from the previous version of the standard or that additions to the standard are anticipated. Because standards often reference other standards, it is important that paragraph numbers remain consistent.Section 1910.308(a) -Systems over 600 Volts, NominalParagraphs (a) (1) through (4) of this section cover the general requirements for all circuits and equipment operated at over 600 volts. 1910.308(a)(1) -Wiring Methods for Fixed Installations (i) -Above-ground conductors shall be installed in rigid metal conduit, in intermediate metal conduit, in cable trays, in cablebus, in other suitable raceways, or as open runs of metal-clad cable suitable for the use and purpose. However, open runs of non-metallic-sheathed cable or of bare conductors or busbars may be installed in locations accessible only to qualified persons. Metallic shielding components, such as tapes, wires, or braids for conductors, shall be grounded. Open runs of insulated wires and cables having a bare lead sheath or a braided outer covering shall be supported in a manner designed to prevent physical damage to the braid or sheath. (ii) -Conductors emerging from the ground shall be enclosed in approved raceways. (See 1910.302(b)(3).) 1910.308(a)(2) -Interrupting and Isolating Devices (i) -Circuit breaker installations located indoors shall consist of metal-enclosed units or fire-resistant cell-mounted units. In locations accessible only to qualified personnel, open mounting of circuit breakers is permitted. A means of indicating the open and closed position of circuit breakers shall be provided. (ii) -Fused cutouts installed in buildings or transformer vaults shall be of a type approved for the purpose. They shall be readily accessible for fuse replacement. (iii) -A means shall be provided to completely isolate equipment for inspection and repairs. Isolating means which are not designed to interrupt the load current of the circuit shall be either interlocked with an approved circuit interrupter or provided with a sign warning against opening them under load. 1910.308(a)(3) -Mobile and Portable Equipment (i) -Power Cable Connections to Mobile Machines. A metallic enclosure shall be provided on the mobile machine for enclosing the terminals of the power cable. The enclosure shall include provisions for a solid connection for the ground wire(s) terminal to effectively ground the machine frame. The method of cable termination used shall prevent any strain or pull on the cable from stressing the electrical connections. The enclosure shall have provision for locking so only authorized qualified persons may open it and shall be marked with a sign warning of the presence of energized parts. (ii) -Guarding Live Parts. All energized switching and control parts shall be enclosed in effectively grounded metal cabinets or enclosures. Circuit breakers and protective equipment shall have the operating means projecting through the metal cabinet or enclosure so these units can be reset without locked doors being opened. Enclosures and
Design Safety Standards for Electrical Systems: Special Systems -OSHA Standard 1910.308 3metal cabinets shall be locked so that only authorized qualified persons have access and shall be marked with a sign warning of the presence of energized parts. Collector ring assemblies on revolving-type machines (shovels, draglines, etc.) shall be guarded. 1910.308(a)(4) -Tunnel Installation (i) -Application. The provisions of this paragraph apply to installation and use of high-voltage power distribution and utilization equipment which is portable and/or mobile, such as substations, trailers, cars, mobile shovels, draglines, hoists, drills, dredges, compressors, pumps, conveyors, and underground excavators. (ii) -Conductors. Conductors in tunnels shall be installed in one or more of the following: (A) -Metal conduit or other metal raceway, (B) -Type MC cable, or (C) -Other approved multiconductor cable. Conductors shall also be so located or guarded as to protect them from physical damage. Multiconductor portable cable may supply mobile equipment. An equipment grounding conductor shall be run with circuit conductors inside the metal raceway or inside the multiconductor cable jacket. The equipment grounding conductor may be insulated or bare. (iii) -Guarding Live Parts. Bare terminals of transformers, switches, motor controllers, and other equipment shall be enclosed to prevent accidental contact with energized parts. Enclosures for use in tunnels shall be drip-proof, weatherproof, or submersible as required by the environmental conditions. (iv) -Disconnecting Means. A disconnecting means that simultaneously opens all ungrounded conductors shall be installed at each transformer or motor location. (v) -Grounding and Bonding. All nonenergized metal parts of electric equipment and metal raceways and cable sheaths shall be effectively grounded and bonded to all metal pipes and rails at the portal and at intervals not exceeding 1000 feet throughout the tunnel.Section 1910.308(b) -Emergency Power Systems1910.308(b)(1) -Scope. The provisions for emergency systems apply to circuits, systems, and equipment intended to supply power for illumination and special loads, in the event of failure of the normal supply. 1910.308(b)(2) -Wiring Methods. Emergency circuit wiring shall be kept entirely independent of all other wiring and equipment and may not enter the same raceway, cable, box, or cabinet or other wiring except either where common circuit elements suitable for the purpose are required, or for transferring power from the normal to the emergency source. 1910.308(b)(3) -Emergency Illumination. Where emergency lighting is necessary, the system shall be so arranged that the failure of any individual lighting element, such as the burning out of a light bulb, cannot leave any space in total darkness.Section 1910.308(c) -Class 1, Class 2, and Class 3 Remote Control, Signaling, and Power-limited Circuits1910.308(c)(1) -Classification. Class 1, Class 2, or Class 3 remote control, signaling, or power-limited circuits are characterized by their usage and electrical power limitation which differentiates them from light and power circuits. These circuits are classified in accordance with their respective voltage and power limitations as summarized in paragraphs (c)(1)(i) through (c)(1)(iii) of this section. (i) -Class 1 Circuits (A) -A Class 1 power-limited circuit is supplied from a source having a rated output of not more than 30 volts and 1000 volt-amperes. (B) -A Class 1 remote control circuit or a Class 1 signaling circuit has a voltage which does not exceed 600 volts; however, the power output of the source need not be limited.
Design Safety Standards for Electrical Systems: Special Systems -OSHA Standard 1910.308 4(ii) -Class 2 and Class 3 Circuits (A) -Power for Class 2 and Class 3 circuits is limited either inherently (in which no overcurrent protection is required) or by a combination of a power source and overcurrent protection. (B) -The maximum circuit voltage is 150 volts AC or DC for a Class 2 inherently limited power source, and 100 volts AC or DC for a Class 3 inherently limited power source. (C) -The maximum circuit voltage is 30 volts AC and 60 volts DC for a Class 2 power source limited by overcurrent protection, and 150 volts AC or DC for a Class 3 power source limited by overcurrent protection. (iii) -The maximum circuit voltages in paragraphs (c)(1)(i) and (c)(1)(ii) of this section apply to sinusoidal AC or continuous DC power sources, and where wet contact occurrence is not likely. 1910.308(c)(2) -Marking. A Class 2 or Class 3 power supply unit shall be durably marked where plainly visible to indicate the class of supply and its electrical rating. (See 1910.302(b)(3).)Section 1910.308(d) -Fire Protective Signaling Systems(See 1910.302(b)(3).) 1910.308(d)(1) -Classifications. Fire protective signaling circuits shall be classified either as non-power limited or power limited. 1910.308(d)(2) -Power Sources. The power sources for use with fire protective signaling circuits shall be either power limited or nonlimited as follows: (i) -The power supply of non-power-limited fire protective signaling circuits shall have an output voltage not in excess of 600 volts. (ii) -The power for power-limited fire protective signaling circuits shall be either inherently limited, in which no overcurrent protection is required, or limited by a combination of a power source and overcurrent protection. 1910.308(d)(3) -Non-Power-Limited Conductor Location. Non-power-limited fire protective signaling circuits and Class 1 circuits may occupy the same enclosure, cable, or raceway provided all conductors are insulated for maximum voltage of any conductor within the enclosure, cable, or raceway. Power supply and fire protective signaling circuit conductors are permitted in the same enclosure, cable, or raceway only if connected to the same equipment. 1910.308(d)(4) -Power-Limited Conductor Location. Where open conductors are installed, power-limited fire protective signaling circuits shall be separated at least 2 inches from conductors of any light, power, Class 1, and non-power-limited fire protective signaling circuits unless a special and equally protective method of conductor separation is employed. Cables and conductors of two or more power-limited fire protective signaling circuits or Class 3 circuits are permitted in the same cable, enclosure, or raceway. Conductors of one or more Class 2 circuits are permitted within the same cable, enclosure, or raceway with conductors of power-limited fire protective signaling circuits provided that the insulation of Class 2 circuit conductors in the cable, enclosure, or raceway is at least that needed for the power-limited fire protective signaling circuits. 1910.308(d)(5) -Identification. Fire protective signaling circuits shall be identified at terminal and junction locations in a manner which will prevent unintentional interference with the signaling circuit during testing and servicing. Power-limited fire protective signaling circuits shall be durably marked as such where plainly visible at terminations.Section 1910.308(e) -Communications Systems1910.308(e)(1) -Scope. These provisions for communication systems apply to such systems as central-station-connected and non-central-station-connected telephone circuits, radio and television receiving and transmitting equipment, including community antenna television and radio distribution systems, telegraph, district messenger, and outside wiring for fire and burglar
Design Safety Standards for Electrical Systems: Special Systems -OSHA Standard 1910.308 5alarm, and similar central station systems. These installations need not comply with the provisions of 1910.303 through 1910.308(d), except 1910.304(c)(1) and 1910.307(b). 1910.308(e)(2) -Protective Devices (i) -Communication circuits so located as to be exposed to accidental contact with light or power conductors operating at over 300 volts shall have each circuit so exposed provided with a protector approved for the purpose. (ii) -Each conductor of a lead-in from an outdoor antenna shall be provided with an antenna discharge unit or other suitable means that will drain static charges from the antenna system. 1910.308(e)(3) -Conductor Location (i) -Outside of Buildings (A) -Receiving distribution lead-in or aerial-drop cables attached to buildings and lead-in conductors to radio transmitters shall be so installed as to avoid the possibility of accidental contact with electric light or power conductors. (B) -The clearance between lead-in conductors and any lightning protection conductors may not be less than 6 feet. (ii) -On Poles. Where practicable, communication conductors on poles shall be located below the light or power conductors. Communications conductors may not be attached to a crossarm that carries light or power conductors. (iii) -Inside of Buildings. Indoor antennas, lead-ins, and other communication conductors attached as open conductors to the inside of buildings shall be located at least 2 inches from conductors of any light or power or Class 1 circuits unless a special and equally protective method of conductor separation, approved for the purpose, is employed. 1910.308(e)(4) -Equipment Location. Outdoor metal structures supporting antennas, as well as self-supporting antennas such as vertical rods or dipole structures, shall be located as far away from overhead conductors of electric light and power circuits of over 150 volts to ground as necessary to avoid the possibility of the antenna or structure falling into or making accidental contact with such circuits. 1910.308(e)(5) -Grounding (i) -Lead-in Conductors. If exposed to contact with electric light and power conductors, the metal sheath of aerial cables entering buildings shall be grounded or shall be interrupted close to the entrance to the building by an insulating joint or equivalent device. Where protective devices are used, they shall be grounded in an approved manner. (ii) -Antenna Structures. Masts and metal structures supporting antennas shall be permanently and effectively grounded without splice or connection in the grounding conductor. (iii) -Equipment Enclosures. Transmitters shall be enclosed in a metal frame or grill or separated from the operating space by a barrier, all metallic parts of which are effectively connected to ground. All external metal handles and controls accessible to the operating personnel shall be effectively grounded. Unpowered equipment and enclosures shall be considered grounded where connected to an attached coaxial cable with an effectively grounded metallic shield.