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Unformatted text preview: t be appropriate for the voltage and tough enough for the environment. Connections need to be reliable and protected. Use the right gauge and type of wire. AWG--American Wire Gauge-- a measure of wire size 14 AWG 20 amps 12 AWG 12 AWG (stranded) (solid) 25 amps 10 AWG 30 amps 8 AWG 40 amps 6 AWG 55 amps 2 AWG 95 amps 1/0 AWG 125 amps Wires come in different gauges. The maximum current each gauge can conduct safely is shown. Section 7 Page 41 S AF ET Y M O D EL S TAG E 3--C O N T rOLLING HAZArDS: SAFE WOrK ENVIrON M EN T Control hazards of fixed wiring
The wiring methods and size of conductors used in a system depend on several factors: Intended use of the circuit system Building materials Size and distribution of electrical load Location of equipment (such as underground burial) Environmental conditions (such as dampness) Presence of corrosives Temperature extremes fixed wiring--the permanent wiring installed in homes and other buildings Fixed, permanent wiring is better than extension cords, which can be misused and damaged more easily. NEC requirements for fixed wiring should always be followed. A variety of materials can be used in wiring applications, including nonmetallic sheathed cable (Romex), armored cable, and metal and plastic conduit. The choice of wiring material depends on the wiring environment and the need to support and protect wires. Aluminum wire and connections should be handled with special care. Connections made with aluminum wire can loosen due to heat expansion and oxidize if they are not made properly. Loose or oxidized connections can create heat or arcing. Special clamps and terminals are necessary to make proper connections using aluminum wire. Antioxidant paste can be applied to connections to prevent oxidation. Control hazards of flexible wiring
Use flexible wiring properly Electrical cords supplement fixed wiring by providing the flexibility required for maintenance, portability, isolation from vibration, and emergency and temporary power needs. Nonmetallic sheathing helps protect wires from damage. Page 42 Section 7 Flexible wiring can be used for extension cords or power supply cords. Power supply cords can be removable or permanently attached to the appliance. flexible wiring--cables with insulated and stranded wire that bends easily A 29-year-old male welder was assigned to work on an outdoor concrete platform attached to the main factory building. He wheeled a portable arc welder onto the platform. Since there was not an electrical outlet nearby, he used an extension cord to plug in the welder. The male end of the cord had four prongs, and the female end was spring-loaded. The worker plugged the male end of the cord into the outlet. He then plugged the portable welder's power cord into the female end of the extension cord. At that instant, the metal case around the power cord plug became energized, electrocuting the worker. An investigation showed that the female end of the extension cord was broken. The spring, cover plate, and part of the casing were missing from the face of the female connector. Also, the grounding prong on the welder's power cord plug was so severely bent that it slipped outside of the connection. Therefore, the arc welder was not grounded. Normally, it would have been impossible to insert the plug incorrectly. But, since the cord's female end was damaged, the "bad" connection was able to occur. Do not let this happen to you. Use these safe practices: Thoroughly inspect all electrical equipment before beginning work. Do not use extension cords as a substitute for fixed wiring. In this case, a weatherproof receptacle should have been installed on the platform. Use connectors that are designed to stand up to the abuse of the job. Connectors designed for light-duty use should not be used in an industrial environment. DO NOT use flexible wiring in situations where frequent inspection would be difficult, where damage would be likely, or where longterm electrical supply is needed. Flexible cords cannot be used as a substitute for the fixed wiring of a structure. Flexible cords must not be . . . run through holes in walls, ceilings, or floors; run through doorways, windows, or similar openings (unless physically protected); attached to building surfaces (except with a tension take-up device within 6 feet of the supply end); hidden in walls, ceilings, or floors; or hidden in conduit or other raceways. Don't use flexible wiring where it may get damaged. Section 7 Page 43 S AF ET Y M O D EL S TAG E 3--C O N T rOLLING HAZArDS: SAFE WOrK ENVIrON M EN T Use the right extension cord The gauge of wire in an extension cord must be compatible with the amount of current the cord will be expected to carry. The amount of current depends on the equipment plugged into the extension cord. Current ratings (how much current a device needs to operate) are often printed on the nameplate. If a power rating is given, it is necessary to divide the power rating in watts by the...
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- Spring '09